web.uettaxila.edu.pk · ii FATIGUE BEHAVIOR OF PIEZOELECTRIC CERAMICS MATERIAL Author Riffat Asim Pasha 03-UET/PhD-ME-03 A dissertation submitted in partial fulfillment of the requirements

FATIGUE BEHAVIOR OF PIEZOELECTRIC CERAMICS MATERIAL

Author Riffat Asim Pasha

03-UET/PhD-ME-03

Supervisor Dr. M. Zubair Khan

Department of Mechanical Engineering

Faculty of Mechanical & Aeronautical Engineering University of Engineering and Technology

Taxila, Pakistan 2009

ii

FATIGUE BEHAVIOR OF PIEZOELECTRIC CERAMICS MATERIAL

Author Riffat Asim Pasha

03-UET/PhD-ME-03

A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (PhD) in Mechanical Engineering.

Checked and Recommended by:

a. The Research Committee:

Dr. M. Zubair Khan Research Supervisor

Dr. M. Asif Khan Dr Muhammad Shuaib Dr Zafarullah Koreshi Member Member Member

b. Foreign Experts i. Dr A.N.K Jadoon ii. Prof.Dr Muhammad Sarwar

U.K U.K Approved By

Dr M. Zubair Kkan Supervisor

External Examiner External Examiner Dr Zafar M. Khan Prof. Dr Arshad Hussain Qureshi

iii

ACKNOWLEDGEMENTS

Alhamdulillah-ha- Rabal Aalamin, who gives me knowledge, wisdom and courage to

complete this research work. May Allah make this work useful for me and for others in

future (Aamin).

After this I would like to say special thanks to my supervisor Dr M. Zubair Khan who

provide me the knowledge and guidance, motivated me in crucial periods and encourage

me at each and every moment during this research work. His continuous involvement and

invaluable suggestions are remarkable.

My special thanks and gratitude is for Prof. Dr Tahir I Khan (Mechanical and

Manufacturing Engineering Department, University of Calgary, Canada). In fact I was

able to do the experimental work due to his kind invitation and supervision of my work

during my stay in Canada. He is really a source of inspiration for me which I can never

forget. I am also thankful to my research committee members, Dr. M.Asif Khan, Dr

Muhammad Shuaib, and Dr Zafrullah Koreshi, who provided me continuous guidance

and invaluable suggestions during my research work.

I am thankful to Dr A.N.K Jadoon and Prof. Dr Muhammad Sarwar for their invaluable

suggestions and evaluation of my thesis. I have best regards for Prof. M. Anwar Khan,

and Prof. Dr Mukhtar Hussain. Sahir, they always motivated me to complete this work. I

am really thankful to Prof. Dr Shahab Khushnood, for his continuous encouragement and

kept me relaxed from the additional academic and administrative load during my research

period. I am grateful to Prof. Dr. M.M.I Hammouda for his invaluable guidance and extra

ordinary help and motivations.

iv

I am thankful to Dr Zafar M Khan and Prof. Dr Arshad Hussain Qureshi for conducting

the defense and oral examination and given valuable suggestions to incorporate in my

thesis.

I must thank to Higher Education Commission, Pakistan for funding to visit University of

Calgary, Canada as visiting research fellow for six months. I must appreciate the great

help by Dr Keler (Electrical Engineering Department, University of Calgary) who

provide the facility to take electrical measurement in his laboratory. I can not forget the

invaluable assistance of Mr Jim Mcneely (Calgary University), who fully cooperated in

technical assistance during all my experimentation. I appreciate assistance of Mr. Abdul

Aziz (Calgary University) in research laboratory. I am thankful to Dr Azfar Hassan

(Chemical Engg. Deptt.(Calgary University) for his cooperation.

I must thankful to Director Research Prof. Dr Qaiser-uz Zaman and his staff members Mr

Zafar Iqbal and Mr Zaheer Shah for their continuous support in fulfilling the

documentation and funding requirements. I must remember my friends Dr Jahanzaib

Mirza, Zahid Suleman Butt and Dr. Gulistan Raja for their continuous moral support and

assistance in editing. I am also thankful to Mr Khalid Mehmood, Mr Zahid Iqbal, Irfan

Ali, Muhammad Irfan and Jam Muhammad Nadeem Ahsan for their support and

assistance.

At the end I express me deepest gratitude to my mother who always pray for my success

and my other family members. I must thank to my wife for her patience during my

research commitments, specially during my stay abroad she managed the home very well

and definitely my kids Ramla and Sharjeel, those suffered a lot and scarified their time

during my whole research period.

v

DECLARATION

It is certified that PhD research work titled “Fatigue Behavior of Piezoelectric

Ceramics Material” is my own work. The work has not been presented elsewhere for

assessment. The material used from any other source has been properly acknowledged.

Author

vi

ABSTRACT Piezoelectric ceramics materials are extensively used in many electromechanical systems

as sensing and actuating devices. The performance of these devices deteriorates due to

cyclic loading either mechanical, electrical, electromechanical, thermo-mechanical, and

under thermal shocking conditions. Earlier the effect of electrical and mechanical cycling

loadings on the functional performance has been investigated. The properties of

commercial lead zirconate titanate degrade during such cycling. However degradation

phenomenon of piezoelectric material during thermal shocking is still an area which has

to be explored. The decay in functional properties of materials is somewhat called

degradation and this terminology used to describe the loss in performance with time due

to stress and temperature. The common phenomenon of degradation is aging of the

material, which affects the performance of the material with time. This change in

performance is thought to be due to re-orientation of dipoles in different configurations.

Environment is another degradation phenomenon influence the performance of piezo

devices. Output performance of piezoelectric materials changes frequently with the

change in temperature, pressure, humidity and moisture. Recently many studies show that

water has the profound effect on the performance of piezoelectric materials. Reliability of

these smart materials is important and hence there is a requirement to have an extensive

study on its functional performance and properties. In actuators mostly disc shaped

piezoelectric are used due to their improved properties. A part of this particular research

work was to investigate the degradation of thin lead zirconate titanate piezoelectric discs

through a series of experimentation to observe its function at variable frequencies in

simple tap water, de-ionized water and sodium chloride (NaCl) solutions. Output

vii

performance has been monitored in real time as peak-peak voltage change. PZT disc

found sensitive in performance in various solutions at different frequencies. The results

obtained can be utilized as qualitative data for designing of micro electromechanical

systems.

The change in capacitance has been measured by using relevant instrumentation during

thermal shocking in de- ionized water. The change in capacitance is a measure of

dielectric constant and other piezoelectric properties. Dielectric constant, impedance,

tangent loss and dissipation factors are the required parameters and can be measured by

using suitable size and shape of piezoelectric materials. In general, piezoelectric ceramics

posses the largest electromechanical coupling factor, dielectric constant and lowest

dielectric loss. The sudden change in temperature may experience a thermal stress which

further changes its above stated properties. Most of the properties are attributed to change

in capacitance values at resonance and anti resonance frequencies. In a part of this

research work, focus was to determine the various piezoelectric properties by thermal

shocking in de-ionized water at resonance frequencies.

In another phase piezoelectric ceramics disc has been investigated for its sensitivity at

different temperatures and at different frequencies and resistances. A model has been

developed to indicate the effect of resistance band at different temperatures. The model of

performance characteristics of thin PZT disc under different temperature conditions is a

unique finding and may used in selection of particular frequency and resistance range for

many piezo devices for the stated conditions.

The objective of this research work was to explore the degradation of thin PZT

piezoelectric ceramics disc in its performance and change of various piezoelectric

viii

properties during thermal cycling and shocking. The present work uncovers the various

unattended thermal cycling and shocking condition of stated piezoelectric material.

Comprehensive data obtained by real time experimentation may useful for designing of

various micro-electromechanical systems.

ix

TABLE OF CONTENTS

CHAPTER Description Page

Title page i

Title page with signatures ii

Acknowledgements …..iii

Declaration ……v

Abstract vi

Table of contents .ix

List of Figures xiv

List of Tables xviii

1 Introduction

1.1 Introduction………………………………………………………………01

1.2 Research Theme……………………..……………………………...........01

1.3 Aims and Objectives of Research………………………..………………02

1.4 Thesis Organization………………………………………………...........04

2 Literature Review

2.1 Introduction………………………………………………………………05

2.2 Piezoelectricity……………………………………………………...........05

2.3 Polarization….……………………………………………………...........07

2.4 Mathematical Description of Piezoelectric Effect ………………...........08

2.5 Historical Background…………………………………………………...11

x

2.6 General Characteristic, Fabrication and Processing of PZT……………...13

2.7 Piezoelectric Crystal Classes………………………………………….....19

2.7.1 Lead Zirconate Titanate (PZT)………………………………......20

2.7.2 Barium Titanate……………………………………………….....21

2.7.3 Polyvinylidene Fluoride (PVDF)……………………………...…22

2.8 Recent Development in Piezoelectric Ceramics………………………....22

2.9 Thermal Cycling and Shocking in Piezoelectric…………………………25

2.10 Effect of Water and Moistures in Piezoelectric Ceramics……………….29

3 Experimental Methodologies

3.1 Introduction…………………………………………………..………..…31

3.2 Standard Fatigue Testing Methodologies……………..………………....31

3.3 Thermal Cyclic Loading in Piezoelectric Ceramics……………………..32

3.4 Selection of Specimen………………………………………….………..33

3.5 Resonance Method………………………………………………………34

3.5.1 Measurement of Material Properties………………………..…..35

3.5.2 Density Calculation……………………………………….….....39

3.5.3 Calculation of Free Relative Dielectric Constant………….……39

3.5.4 Calculation of Coupling……………………………..……….....39

3.6 Determination of Elastic, Piezoelectric, and Dielectric Constant …..….40

3.7 Selection of Experimental Setup/Design of Experiments………….......40

3.7.1 Phase-1 Performance of PZT and Its Effect Due to Water…….41

3.7.2 Phase-2 Thermal Cycling/Shocking Effect of Thin PZT Disc....41

3.7.3 Phase-3 Thermal Cycling Effect…………………………….....42

xi

3.8 Research Contribution…………………………………………….…....42

3.8.1 Phase-1……………………………………………………........42

3.8.2 Phase-2……………………………………………………........42

3.8.3 Phase-3……………………………………………………........43

3.9 Measurements……………………………………………………….…43

3.10 Capacitance Measurement by 6451B Dielectric Test Fixture…………44

3.10.1 Specifications……………………………………………….....44

3.10.2 Performance Characteristics……………………………....…..45

3.10.3 Selection of Electrodes…………………………………..…....45

3.10.4 Operation………………………………………………………46

3.10.5 Contacting Electrode Method………………………………….46

3.10.6 Testing Material……………………………………………….46

3.10.7 Error Correction……………………………………………….47

3.10.8 Electrode Adjustment…………………………………………47

3.10.9 Measurement Procedure………………………………………47

3.11 Designed Circuitry for Frequency Determination……………………48

3.11.1 Switch Box Circuit……………………………………….…..49

3.11.2 Oscillator Circuit……………………………………..…........52

3.11.3 Frequency Counter…………………………………………...53

3.11.4 Decade Resistor Circuit……………………………………....53

3.11.5 Wave Form Generator………………………………..……....55

3.11.6 Voltmeter………………………………………………..........55

3.11.7 Frequency Measuring Procedure………………………..........55

xii

3.12 Measurement and Effect of Thickness by ANSYS……………………..57

4 Experimentation and Analysis of Results

4.1 Introduction………………………………………..……………58

4.2 Phase-1………………………………………………………....58

4.2.1 Piezoelectric Material…………………………..……...............61

4.2.2 Test Setup and Variables………………………….……….…..62

4.2.3 Results and Discussion……………………………….……..…64

4.3 Phase-2 (Series 1)……………………………………………...82

4.3.1 Specimen………………………………………………………82

4.3.2 Instrumentation……………………………………………......82

4.3.3 Testing /Measurements………………………………………..82

4.4 Thermal Shocking from 1000C from Thermal Chamber to De-Ionize

Water at 200C………………………………………………..…………..…...83

4.4.1 Test Setup &Variables……………………………………….85

4.4.2 Results Analysis…………………………..………………….88

4.5 Phase-2 (series 2)……………………………………………............95

4.5.1 Experimentation…………………………………………..…95

4.5.2 Results Analysis……………………………………………..97

4.6 Phase-3 (series 3)…………………………………………….……..101

4.6.1 Experimental Setup………………………………....102

4.6.2 Experimentation………………………………….…105

4.6.3 Series-1 (at room temperature, 200C)………………106

xiii

4.6.4 Series-2 (at 160 0C)……………………………..........111

4.6.5 Development of a Model……………………..….…..118

4.7 Discussions…………………………………………………………..126

4.7.1 Effect of Water on PZT Disc………………………………….…...….126

4.7.2. Thermal Cycling/Shocking of Thin PZT Disc [From 100 0C (Thermal

chamber ) to 20 0C (In de-ionized water)]……………………………..........127

4.7.3 Thermal Cycling/Shocking of Thin PZT Disc From 100 0C &150 0C

(Thermal chamber) to20 0C (In de-ionized water)……………………….....130

4.7.4 Effect of Frequency and Resistance on peak-peak voltage in two different

Thermal Conditions………………………………………………………….131

5 Conclusions and Future Recommendations

5.1 Conclusions 132

5.2 Future Recommendations 134

References………………………………………………………………….… 137

APPENDIX-A: Thermal cycling/shocking results images of thin PZT disc APPENDIX-B: List of Pertinent PhD Publications.

xiv

LIST OF FIGURES

Fig.2.1 Phase Stability in the System Pb(Ti1-x Zrx)O3 ...................................................... 14

Fig.2.2 Coupling Coefficient kp and Permittivity εr Values Across the PZT Compositional

Range ...................................................................................................................................... 15

Fig.3.1 Experimental circuit for the determination of fm and fn ......................................... 49

Fig. 3.2 Switch Box Circuit................................................................................................... 50

Fig. 3.3 Oscillator circuit ....................................................................................................... 52

Fig. 3.4 Decade resistor circuit ....................................................................................... 54

Fig. 3.5 Waveform Generator ....................................................................................... 54

Fig. 4.1 Schematic Arrangement for the determination of Pk-Pk Voltage at variable

frequencies ............................................................................................................................. 62

Fig. 4.2 Variation of peak to peak voltage as a function of frequency. ............................. 63

Fig. 4.3 Heating time as a function of peak to peak voltage in ordinary water. ............... 76

Fig. 4.4 The change in voltage as a function of drying time after immersion in ordinary

water……………………………………………………………………………………...76

Fig. 4.5 Heating time as a function of peak to peak voltage in de-ionized water. ............. 77

Fig. 4.6 The change in voltage as a function of drying time after immersion in de-ionized

water. ...................................................................................................................................... 77

Fig.4.7 Heating time as a function of peak to peak voltage in NaCl

solution…………………………………………………………………………………..78

Fig. 4.8 The change in voltage as a function of drying time after immersion in NaCl

solution. .................................................................................................................................. 78

Fig. 4.9 Rate of change in temperature and shocking ......................................................... 85

xv

Fig. 4.10 Impedance analyzer connected with test fixture for measuring various

parameters (Impedance, Capacitance, Dissipation factor, Phase angle). ........................... 88

Fig. 4.11 Value of capacitance for Un-shocked Disc ……………………………………90

(a). Capacitance at frequency of maximum impedance

(b). Capacitance at frequency of minimum impedance

Fig. 4.12 Value of capacitance after thirty five shocks……………………..……………91



Fig. 4.13 Change in Dielectric constant against Number of shocks…………………..…92

Fig. 4.14 Coupling Factors against Number of Shocks ....................................................... 92

Fig. 4.15 Change in dielectric constant against number of shocks, at frequency 1KHz, at

frequency of maximum impedance, at frequency of minimum impedance. ..................... 98

Fig. 4.16 Change in coupling factor (K31, Keff) against number of shocks from 1000C –

200C & from 1500C – 200C in de-ionized water.. ............................................................... 99

Fig. 4.17 Change in Modulus of impedance ( |Z| ) against number of shocks from 1000C –

200C & from 1500C – 200C in de-ionized water.. ............................................................... 99

Fig. 4.18 Experimental arrangement for the determination of out put voltage ................ 103

Fig. 4.19 Schematic arrangement of thermal cycling circuitry .......................................... 104

Fig. 4.20 Soldered Piezoelectric PZT disc (diameter 12.7mm and thickness 0.191mm) .. 106

Fig. 4.21 Experimental arrangement for the determination of output voltage at room

temperature (200C) . ............................................................................................................ 107

Fig. 4.22 Effect of resistance on Pk-Pk voltage at various frequencies at 200C………..108

Fig. 4.23 Change in Pk-Pk voltage for each 100kΩband at 200C……………………...110

xvi

Fig. 4.24 Effect of resistance at Pk-Pk voltage at various frequencies and at 1600C ...... 113

Fig. 4.25 Change in Pk-Pk voltage for each 100kΩ band at 1600C…………………….114

Fig. 4.26 Effect of temperature on Pk-Pk Voltage at frequency 50 Hz against change in

Resistance……………………………………………………………………………....115

Figure 4.27 Effect of temperature on Pk-Pk Voltage at frequency 100 Hz against change

in Resistance……………………………………………………………………………115


in Resistance……………………………………………………………………………116


in Resistance………………………………………………………………………..…..116


in Resistance………………………………... ………………………………………...117

Figure. 4.31 Difference in Pk-Pk value against Resistance band number at 50Hz……119

Figure. 4.32 Difference in Pk-Pk value against Resistance band number at 100Hz…..120




Figure. 4.36 Exponential coefficient A against Frequency in Hz at 200C…………….122

Figure 4.37 Exponential coefficient B against Frequency in Hz at 200C……………..122

Figure. 4.38 Difference in Pk-Pk value against Resistance band number at 50Hz……123


Figure. 4.40 Difference in Pk-Pk value against Resistance band number at150Hz……124

Figure. 4.41 Difference in Pk-Pk value against Resistance band number at 200Hz…...124

xvii

Figure.4.42 Difference in Pk-Pk value against Resistance band number at 300Hz……124

Figure-4.43 Exponential coefficient A against Frequency in Hz at 200C……………...125

Figure-4.44 Exponential coefficient A against Frequency in Hz at 200C ……………..125

xviii

LIST OF TABLES

Table 3.1: Description of Specimen (PSI-5A4E Single Layer Disks) ............................... 33

Table 3.2 Parent Specimen Properties as provided by supplier (PIEZO SYSTEM INC. USA)…..34

Table 3.3 Description of various electrodes and their selection…………………………45

Table3.4 Selection of Resistance in Switch-2……………………………………...……51

Table3.5 Selection of Resistance for Switch I & Switch II………………………… …54 Table 4.1 Heating time in ordinary water and respective voltage at 50Hz ........................ 65

Table 4.2 Heating time in ordinary water and respective voltage at 100Hz ...................... 65

Table 4.3 Heating time in ordinary water and respective voltage at 150Hz……………..66 Table 4.4 Heating time in ordinary water and respective voltage at 200Hz…… ………66

Table 4.5 Drying Time after taking out from ordinary water at 50Hz…………………...66

Table 4.6 Drying Time after taking out from ordinary water at 100Hz ............................. 67

Table 4.7 Drying Time after taking out from ordinary water at 150Hz ............................. 67

Table 4.8 Drying Time after taking out from ordinary water at 200Hz…………………67 Table 4.9 Heating Time in De-ionized water and respective voltage at 50Hz………….68 Table 4.10 Heating Time in De-ionized water and respective voltage at 100Hz .............. 68

Table 4.11 Heating Time in De-ionized water and respective voltage at 150Hz………..68

Table 4.12 Heating Time in De-ionized water and respective voltage at 200Hz………..69

Table 4.13 Drying time after taking out from de-ionized water at various frequencies…69

Table 4.14 Heating Time in NaCl solution and respective voltage at 50&100Hz…...….70

Table 4.15 Heating Time in NaCl solution and respective voltage at 150&200Hz…….70

Table 4.16 Drying Time after taking out from NaCl solution at 50 & 100Hz…………..71

xix

Table 4.17 Drying Time after taking out from NaCl solution at 150 & 200Hz……..…73

Table-4.18 Values of Capacitance, Coupling factors ,and dielectric constant at frequency

of maximum (fm) and frequency of minimum (fn) impedance………………………....87

Table-4.19 Change in Dielectric Constant and Coupling Factor for two Different Thermal

Shocking Conditions…………………………………………………………………...97

Table-4.20 Change in Pk-Pk Voltage against Resistances at 200C (RT)*………….…107

Table 4.21 Difference in voltage for each 100kΩ band at 200C………………………109

Table 4.22 Resistance Range Bands………………………………………………..…110

Table-4.23 Change in Pk-Pk Voltage against Resistances at 1600C………………….112

Table-4.24: Difference in voltage for each 100kΩ band at 1600C…………………....113

1

CHAPTER # 1

INTRODIUCTION

1.1 Introduction

There has been a growing interest in recent years in piezoelectric ceramics

materials due to their numerous applications. These material exhibits very interesting

behavior for which they are being used extensively in various micro electromechanical

systems as sensing and actuating devices. Micro-electromechanical systems (MEMS) are

playing an important role in the field of electronics and mechatronics. Recently these

systems are manufactured by using natural and synthetic fabricated ceramic crystals. The

structures in which these materials are used are normally under the influence of various

cyclic loads. These cyclic loads may be mechanical, electrical, electromechanical, and

thermal [1]. Most of the piezoelectric ceramic materials are polycrystalline ceramics

instead of natural piezoelectric crystals. These are more versatile with physical, chemical

and piezoelectric characteristics. PZT ceramics can be manufactured to almost any given

shape or size. They are chemically inert, and immune to moisture and other atmospheric

conditions. There are still various conditions in which the behavior of these materials

needs the attention of present researchers.

.

1.2 Research Theme

Piezoelectric materials used in different sensing and actuating devices may

degrades in its properties. These properties may affect the performance and functioning

in their operation. Degradation in their properties due to mechanical and electrical fatigue

2

has been extensively studied and there was a research gap in finding the characteristics of

these materials in thermal cycling and particularly in thermal shocking and quenching.

Lead zirconate titanate (PZT) based ceramics are widely used for their excellent

piezoelectric properties and these properties may degrade due to the application of

mechanical, electrical, electromechanical, and thermal loadings. Lot of work is being

carried out in exploring the fatigue behavior of these smart materials when subjected to

electrical and electromechanical loading conditions. Fatigue studies have shown that the

degradation in material properties is strongly influenced by temperature. Temperature

plays an important role in dictating the electromechanical response of piezoelectric

materials. In this research work, thin PZT discs have been investigated for their cyclic

and shocking behavior in thermal loading conditions. The purpose was to test the PZT

under various thermal environments and examine the degradation in their properties. The

degradation in materials properties affects the functional performance characteristics of

the instrument in which these smart materials are being used.

1.3 Aims and Objectives of Research

The present work aimed to investigate the change in functional performance and internal

characteristics of lead zirconate titanate thin disc during thermal cycling of thin PZT disc

in different conditions. The work has been divided in three major phases of

experimentation. Phase-1 is to determine the change in output potential during thermal

cycling in three different water conditions. Performance of PZT material affected by

environmental factor has been reported. In phase-2 the change in piezoelectric properties

with the change in capacitance and dielectric constant at resonance and anti–resonance

3

frequencies has been examined during thermal shocking in de-ionized water. The results

are the basis for the determination of other piezoelectric properties.

Effect of frequencies and resistances on output potentials at variable temperatures have

been analyzed real time in phase-3. Comprehensive quality data has been obtained which

may used for the designing of smart piezoelectric devices.

By considering the tested and analyzed data, following objectives have been

achieved in this research work.

• To understand the nature and behavior of selected PZT disc during thermal

cycling in different water conditions. (In simple tap water, in de-ionized water and

in NaCl solution).

• To find the change in dielectric constant, capacitance and other piezoelectric

properties by obtaining the quality data at resonance and anti resonance

frequency.

• How thermal shocking in de-ionized water affects the piezoelectric properties of

the selected grade and size of PZT material.

• The effect of thermal shocking temperature difference on its piezoelectric

properties has been investigating through sensitivity analysis.

• Development of a model elaborates the performance characteristics at variable

frequency and resistance bands (0kΩ to 1000kΩ) at two different specific

temperatures.(200C and 1600C)

4

1.4 Thesis Organization

Thesis has been organized as follow:

This chapter is a brief introduction of scope and objectives of this particular research

work. The descriptions of piezoelectricity and mathematical description of piezoelectric

material along with comprehensive literature review has been presented in chapter-2.

This chapter also includes the brief history, applications and the descriptions of the

previous work relating fatigue behavior of piezoelectric ceramics under various loading

conditions. Existing and proposed research methodology, experimental arrangements,

and circuitry design to measure the frequency of maximum and minimum impedance at

various frequencies have been described in chapter 3. All three experimental phases have

been elaborated in chapter 4. In phase-1, effect of water on performance characteristics of

piezoelectric ceramic discs in different mediums has been described. Thermal cycling and

shocking effects have been determined in phase-2. Thermal cycling using variable

frequencies and resistances and at different temperatures has been analyzed in phase-3 of

the same chapter. Results analysis and a mathematical model to describe the behavior of

the material in different conditions have been described in the same chapter. The

elaborated analysis and discussions on results have also been described in the same

chapter. Conclusions and future recommendations are presented in Chapter 5.

Last but not least the current research work is to explore the unattended behaviors of thin

PZT disc in thermal cycling/shocking environment at variable conditions.

5

CHAPTER# 2

LITERATURE REVIEW

2.1 Introduction

Piezoelectric ceramics materials play an important role in the field of smart

structures. The degradation in their internal characteristics affects their efficiency and

performance. This chapter reviews a brief historical background. Piezoelectric crystal

classes, their characteristics. Fabrication and processing techniques have also been

described. A comprehensive review on the degradation behavior of piezoelectric ceramic

subjected to thermal cycling and shocking condition is presented.

2.2 Piezoelectricity

The phenomenon of piezoelectricity was discovered in the late nineteenth century. It was

observed that certain materials generate an electric charge or voltage when they are under

mechanical stress. Alternately, these materials produce a mechanical stress when they are

subjected to an applied voltage [2].

In 1880, Pierre and Jacques Curie experimentally discovered the direct piezoelectric

effect in various naturally occurring substances. In 1881, Hermann Hankel suggested

using the term piezoelectricity, which is derived from the Greek “piezen” meaning “to

press.” In 1893, Willam Thomson published seminal papers on the theory of

piezoelectricity. It was mathematically hypothesized and then experimentally proven that

a material exhibiting both, the generation and actuation effect.

6

Piezoelectricity is a property of certain classes of crystalline materials including natural

crystals and manufactured ceramics such as barium titanate and lead zirconate titanate

(PZT). The piezoelectricity phenomenon was developed and applied in sonar and quartz

oscillation crystals. In 1921, Walter Cady invented the quartz crystal-controlled oscillator

and the narrow band quartz crystal filter used in communication systems. Two important

artificial piezoelectric crystals, barium titanate, and lead zirconate titanate were invented

in the early 1950s [3]. The surface charge leads to mechanical strain either compressive

or tensile depends upon the direction of applied polarity of the applied voltage. The

phenomena occur only in those crystals having no centre of symmetry. As piezoelectric

materials have excellent capability to convert an electrical signal to mechanical and

mechanical to electrical and therefore have high electromechanical coupling factor. A

especially cut electroded piezo crystal detect the longitudinal transverse vibration in

solid. These mechanical vibrations converted to electrical signal and can be displayed on

oscilloscope. One of the most important applications of the piezoelectric material is in the

frequency control of oscillator and filters whenever a mechanical force is setup in these

materials they vibrate at certain frequency. The frequency of these mechanical vibrations

has certain wavelength. These mechanical vibrations have very small losses and therefore

have a high quality factor Q. With the excitation of PZT materials, Impedance at

maximum and minimum frequency is the measure of coupling factor. Higher is the

difference between these two referenced frequencies, higher is the coupling factor

between fm and fn the response of the transducer is controlled by the mass of the material

[4]. Piezoelectric materials are being used in MEMS sensors and actuators. Think-film

piezoelectric materials have been explored for use as on-chip acoustic transducers,

7

pumps, accelerometers, and microphones and mainly as actuators and sensors in the

aerospace and marine industries [2]. The effect also useful application for the production

and detection of sound, generation of high voltages, electronic frequency generation,

microbalance, and ultra fine focusing of optical assemblies [5].

2.3 Polarization

Many important properties of piezoelectric materials stem from their crystalline

structures. Piezoelectric crystals can be considered to be a mass of minute crystallites

(domains). The macroscopic behavior of the crystal differs from that of individual

crystallites, due to the orientation of such crystallites. The direction of polarization

between neighboring crystal domains can differ by 900 or 1800. Owing to the random

distribution of domains throughout the material, no overall polarization or piezoelectric

effect is exhibited. A crystal can be made piezoelectric in any chosen direction by poling,

which involves exposing it to a strong electric field at an elevated temperature. Under the

action of this field, domains most nearly aligned with the field will grow at the expense

of others. The material will also lengthen in the direction of the field, when the field is

removed, the dipoles remain locked in an approximate alignment, and crystal becomes

polarized.

The poling treatment is usually the final step of crystal manufacturing. Care must be

taken in all subsequent handling and use to ensure that the crystal is not depolarized,

since this will result in a partial or even total loss of its piezoelectric effect.

For static fields, the threshold is typically between 200-500 V/mm.

Mechanical depolarization occurs when mechanical stress on a piezoelectric element

becomes high enough to disturb the orientation of the domains and hence destroy the

8

alignment of the dipoles. If a piezoelectric element is heated to a certain threshold

temperature, the crystal vibration may be so strong that domains become disordered and

the element becomes completely depolarized. This critical temperature is called the Curie

point or the Curie temperature. A safe operating temperature would normally be halfway

between 00C and the Curie point. The properties of piezoelectric elements are time

dependent and the stability of a piezoelectric as a function of time is of particular interest

[2]. Piezoelectric materials are crystals. The microscopic origin of piezoelectricity is the

displacement of ionic charges with a crystal, leading to the polarization and electric field.

A stress (tensile or compressive) applied to a piezoelectric crystal will alter the spacing

between centers of positive and negative charge sites in each domain cell; this leads to a

net polarization manifested as open circuit voltages measurable at the crystal surface.

Compressive and tensile stresses will generate electric fields which will exert a force

between the centers of positive and negative charges, leading to an elastic strain and

changes of dimensions depending on the field polarity. The direction of the induced

polarization depend on the direction of applied stress generally the applied stress in one

direction can give rise to induced polarization in other direction and reversing of stress

reverse the polarization direction [4]

2.4 Mathematical Description of Piezoelectric Effect

In a piezoelectric crystal, the constitutive equation that relates electrical polarization (D)

and applied mechanical stress (T) is

D= dT + εE (1.1)

9

Where d is the piezoelectric coefficient matrix, ε the electric permittivity matrix, and E

the electrical field. The electrical polarization is contributed by two parts-one stemming

from electrical biasing and one from mechanical loading.

If no electric field is present (i.e.., E=0), then the second term on the right-hand side of

Equation (1.1) can be eliminated.

The General Constitutive Equation can be written in the full matrix form:

T1 D1 d11 d12 d13 d14 d15 d16 T2 ε11 ε12 ε13 E1 D2 = d21 d22 d23 d24 d25 d26 T3 + ε21 ε22 ε23 E2 D3 d31 d32 d33 d34 d35 d36 T4 ε31 ε32 ε33 E3 T5

T6

The terms T1 through T3 are normal stress along axes 1, 2, and 3, whereas T4 through T6

are shear stresses. The units of electrical displacement (Di) stress (Tj), permittivity (εi),

and electrical field (Ej) are C/m2, N/m2, F/m, and V/m, respectively. The unit of the

piezoelectric constant dij is the unit of electric displacement divided by the unit of the

stress namely.

[ ] [ ][ ]

[ ] [ ][ ] N

Columb

mNmm

TEVF

TDdij ====

2

ε (1.3)

(1.2)

10

Equation 1.4 can be expanded to a full matrix from:

(1.5)

(1.6)

The inverse effect of piezoelectricity can be similarly described by a matrix-form

constitutive equation. In this case, the total strain is related to both the applied electric

field and any mechanical stress, according to

S = ST + dE, (1.4)

Where s is the strain vector and S is the compliance matrix.

If there is no mechanical stress present (Ti,i=1,6=0), the strain is

related to the electric field by

Note that, for any given piezoelectric material, the dij components connecting the strain

and the applied field in the inverse effect are identical to the dij connecting the

polarization and the stress in the direct effect [2]. The unit of dij can be confirmed from

Equation (1.6) as well. It is (m/m)/(V/m = m/V = C/N.

11

The electromechanical coupling coefficient k is a measure of how much energy is

transferred from electrical to mechanical energy, or vice versa, during the actuation

process and is calculated as defined [6].

EnergyConverted

InputEnergyK =2 (1.7)

This relation holds true for both mechanical-to-electrical and electrical-to-mechanical

energy conversion. The magnitude of k is a function of not only the materials, but also the

geometries of the sample and its oscillation mode [2]

2.5 Historical Background

The piezoelectric effect dates back to thousands of years was first noticed in rocks

which would repel other rocks when they were heated. These rocks, which were actually

Tourmaline crystals, eventually found their way into Europe. Once the crystals arrived in

Europe, they were scrutinized by the scientists. In the mid 1700’s, this effect was given

the name of pyroelectricity, which means electricity by heat. Pyroelectricity is the ability

of certain mineral crystals to generate electrical charge when heated, was known as early

as the 19th century, and was named by David Brewster in 1824. In 1880, the brothers

Pierre Curie and Jacques Curie predicted and demonstrated piezoelectricity using tinfoil,

glue, wire, magnets, and a jeweler's saw. They showed that crystals of tourmaline, quartz,

topaz, cane sugar, and Rochelle salt generate electrical polarization from mechanical

stress. Quartz and Rochelle salt exhibited the most piezoelectricity effects. The second

practical application for piezoelectric devices was sonar, first developed during World

War I. In France in 1917, Paul Langevin (whose development now bears his name) and

his fellows developed an ultrasonic submarine detector. The detector consisted of a

12

transducer, made of thin quartz crystals carefully glued between two steel plates, and a

hydrophone to detect the returned echo. By emitting a high-frequency chip from the

transducer, and measuring the amount of time it takes to hear an echo from the sound

waves bouncing off an object, one can calculate the distance to that object. The use of

piezoelectricity in sonar, create an interest in piezoelectric devices. Over the next few

decades, new piezoelectric materials and new applications for those materials were

explored and developed. Development of piezoelectric devices and materials in the

United States was kept within the companies involved in the development, mostly due to

the wartime beginnings of the field, and in the interests of securing profitable patents.

Quartz crystals were the first commercially exploited piezoelectric material, but scientists

searched for higher-performance materials. Piezoelectric devices found homes in many

fields. Ceramic phonograph cartridges simplified player design, were cheap and accurate,

and made record players cheaper to maintain and easier to build. Ceramic electric

microphones could be made small and sensitive. The development of the ultrasonic

transducer allowed for easy measurement of viscosity and elasticity in fluids and solids,

resulting in huge advances in materials research. Ultrasonic time-domain reflecto-meters

(which send an ultrasonic pulse through a material and measure reflections from

discontinuities) could find flaws inside cast metal and stone objects, improving structural

safety. However, despite the advances in materials and the maturation of manufacturing

processes, the United States market had not grown as quickly. Without many new

applications, the growth of the United States' piezoelectric industry suffered. In contrast,

Japanese manufacturers shared their information, quickly overcoming technical and

manufacturing challenges and creating new markets. Japanese efforts in materials

13

research created piezoceramic materials competitive to the U.S. materials, but free of

expensive patent restrictions. Major Japanese piezoelectric developments include new

designs of piezoceramic filters, used in radios and televisions, piezo-buzzers and audio

transducers that could be connected directly into electronic circuits, and the piezoelectric

igniter which generates sparks for small engine ignition systems (and gas-grill lighters)

by compressing a ceramic disc. Ultrasonic transducers that could transmit sound waves

through air had existed for quite some time, but first saw major commercial use in early

television remote controls. These transducers now are mounted on several car models as

an echo location device, helping the driver determine the distance from the rear of the car

to any objects that may be in its path. Historically, well known applications of

piezoelectric sensors have included phonograph pickups, microphones, acoustic modems,

and acoustic imaging for underwater, underground objects and medical instrumentation

[7]. The first ceramic to be developed commercially was BaTiO3. By the 1950s the solid

solution system Pb (Ti, Zr)O3 (PZT), which also the perovskite structure, was found to be

ferroelectric and PZT compositions are now the most widely exploited of all piezoelectric

ceramics [8].

2.6 General Characteristics, Fabrication and Processing of PZT

The Pb (Zr1-x Tix)O3 phase diagram is shown in figure 2.1. The morphotropic

phase boundary (MPB) defines the composition at which there is an abrupt structural

change, the composition being almost independent of temperature. That is the phase

boundary between the high temperature rhombohedral and tetragonal forms is, practically

speaking is a vertical line. As in figure2.1, the piezoelectric activity peaks in the region of

14

the MPB composition and considerable effort has been directed to elucidating the reasons

for this technically very important phenomena.

Figure 2.1: Phase Stability in the System Pb(Ti1-x Zrx)O3 [5]

The current understanding is that the MPB is not a sharp boundary but rather a

temperature dependant compositional range over which there is a mixture of tetragonal

and monoclinic phases. At room temperature (300K) the two phases coexist over the

range 0.455≤ x ≤0.48. The enhanced piezoelectric activity of the commercial

compositions (x=0.48) can be rationalized in terms of the relatively large ionic

displacements associated with stress (electrical or mechanical) induced rotation of the

monoclinic polar axis.

Coupling coefficient and permittivity values across the PZT has been shown in Fig.2.2

15

Figure 2.2: Coupling Coefficient kp and Permittivity εr Values Across the PZT

Compositional Range

Depoling can be achieved by applying a field in the opposite direction to that used

for poling or in some cases by applying a high ac field and gradually reducing it to zero,

but there is a danger of overheating because of high dielectric loss at high fields. Some

compositions can be poled by applying a compressive stress (10-100 MPa). Complete

depoling is achieved by raising the temperature to well above the Curie point and cooling

without a field.

Aging effects are known to be significantly changed when the concentration of

vacant oxygen sites is increased either by doping or by heating in mildly reducing

atmospheres. The dipoles then provide an internal field stabilizing the domain

configuration thereby reducing ageing rate. The material features extremely large

dielectric constants. These properties make PZT-based compounds one of the most

16

prominent and useful electroceramics. Commercially, it is usually not used in its pure

form, rather it is doped with either acceptor dopants, which create oxygen (anion)

vacancies, or donor dopants, which create metal (cation) vacancies and facilitate domain

wall motion in the material. In general, acceptor doping creates hard PZT while donor

doping creates soft PZT. In general, soft PZT has a higher piezoelectric constant, but

larger loss in the material due to internal friction. In hard PZT, domain wall motion is

pinned by the impurities thereby lowering the losses in the material, but at the expense of

a reduced piezoelectric constant. It is used to make ultrasound transducers and other

sensors and actuators, as well as high-value ceramic capacitors. PZT is also used in the

manufacture of ceramic resistors for reference timing in electronic circuitry. The

manufacturing process for high-voltage piezoceramic consists of following steps. The

manufacturing process for high-voltage piezoceramic starts with mixing and ball milling

of the raw materials. Next, to accelerate reaction of the components, the mixture is heated

to 75% of the sintering temperature, and then milled again. Granulation with the binder is

next, to improve processing properties. After shaping and pressing, the green ceramic is

heated to about 750 °C to burn out the binder. The next phase is sintering, at temperatures

between 1250 °C and 1350 °C. Then the ceramic block is cut, ground, polished, lapped,

etc., to the desired shape and tolerance. Electrodes are applied by sputtering or screen

printing processes. The last step is the poling process which takes place in a heated oil

bath at electrical fields up to several kV/mm. In this case the ceramic take on

macroscopic piezoelectric properties [8].

Piezoelectric ceramics are fabricated with powder preparation. Powder preparation and

powder calcining and sintering are the more important processes that influence the

17

material properties. The powder is then pressed to the required shapes and sizes.

Machining, electroding, poling and application of a DC field to orient the dipoles are the

more steps to induce piezoelectricity.

The most common powder preparation is the mixed oxide route. In this process, powder

is prepared from the appropriate stoichiometric mixture of the constituents’ oxide route.

In the case of lead zirconate titanate (PZT): lead oxide, titanium oxide, and zirconium

oxide are the main compounds. Depending on application, various dopants are used to

tailor the properties of interest. PZT ceramics are rarely utilized without the addition of

dopants to modify some of their properties. A-site additives tend to lower the dissipation

factor, which affects heat generation, but also lower the piezoelectric coefficients; for this

reason they are mostly used in ultrasonics and other high frequency applications, B-site

dopants increase the piezoelectric coefficients but also increase the dielectric constant

and loss. They are utilized as actuators in vibration and noise control, benders. Mixing of

the powders can be done by dry-ball milling or wet ball milling. Both methods having

advantages and disadvantages: wet ball-milling is faster than dry-milling; however, the

disadvantage is the added step of liquid removal. The most common method for making

PZT ceramics is through wet-ball milling; ethanol and stabilized zirconia media are

added for a wet milling process. A vibratory mill may be used rather than a conventional

ball mill; it was shown by Herner that this process reduces the risk of contamination by

the balls and the jar [9]. Zirconia media are used to further reduce the contamination

risks. The calcinations step is a very crucial step in the processing of PZT ceramics; it is

important that the crystallization be complete and that the perovskite phase forms during

this step. After calcining, a binder is added to the powder, and then the mixture is shaped

18

usually by dry-pressing in a die for simple shapes, or extrusion, or casting for more

complicated bodies. Next, the shapes are sintered: placed in an oven for binder burn-out

and densification.

The major problem in the sintering of the PZT ceramic is the volatility of PbO at about

800 0C. To minimize this problem, the PZT samples are sintered in the presence of a lead

source, such as PbZrO3, and placed in closed crucibles. The saturation of the sintering

atmosphere with PbO minimizes lead loss from the PZT bodies. Sintering can now be

carried out at temperatures varying between 1200-1300oC. Despite precautions, there is

usually a resulting loss of 2%-3% of the initial lead content.

After cutting and machining into desired shapes, electrodes are applied and a strong DC

field is used to orient the domains in the polycrystalline ceramic. DC poling can be done

at room temperature or at higher temperatures depending on the material and the

composition. The poling process only partially aligns the dipoles in a polycrystalline

ceramic, and the resulting polarization is lower than that for single crystals.

This processing technique presents many uncertainties and the presence of a wide number

of other fabrication techniques is an indication that there is a great need for the

production of reliable PZT ceramics with optimum properties and microstructure. One

problem often encountered is the deviation from stoichiometry. This problem is often due

to impurities present in the raw materials as well as the lead loss during the sintering

processes, which invariably results in substantial alternations of the PZT properties. As a

result, the elastic properties can vary as much as 5%, the piezoelectric properties 10% and

the dielectric properties 20% within the same batch [10]. Also, the piezoelectric and

dielectric properties generally suffer if there is any lack of homogeneity due to poor

19

mixing. It is important then that the constituent oxides be intimately mixed. In the method

described above, however, the constituents are solid solutions and it has been shown that

an intimate mixing of solid solutions is difficult if not impossible. More information on

the preparation of piezoelectric ceramics can be found by Moulson [8] and Jaffe [11].

2.7 Piezoelectric Crystal Classes

Of the thirty-two crystal classes, twenty-one are non-centrosymmetric (not having

a centre of symmetry), and of these, twenty exhibit direct piezoelectricity. Ten of these

are polar (i.e.. spontaneously polarize), having a dipole in their unit cell, and exhibit

pyroelectricity. If this dipole can be reversed by the application of an electric field, the

material is said to be ferroelectric [5].In a piezoelectric crystal, the positive and negative

electrical charges are separated, but symmetrically distributed, so that the crystal overall

is electrically neutral. The domains are usually randomly oriented, but can be aligned

during poling (not the same as magnetic poling), a process by which a strong electric

field is applied across the material, usually at elevated temperatures. When a mechanical

stress is applied, this symmetry is disturbed, and the charge asymmetry generates a

voltage across the material. Crystal is a solid in which the constituent atoms, molecules,

or ions are packed in a regularly ordered, repeating pattern extending in all three spatial

dimensions. Generally, crystals form when they undergo a process of solidification.

Under ideal conditions, the result may be a single crystal, where all of the atoms in the

solid fit into the same crystal structure. However, generally, many crystals form

simultaneously during solidification, leading to a polycrystalline solid.

20

Crystalline structures occur in all classes of materials, with all types of chemical bonds.

Almost all metal exists in a polycrystalline state; amorphous or single-crystal metals must

be produced synthetically, often with great difficulty. Ionically bonded crystals can form

upon solidification of salts, either from a molten fluid or when it condenses from a

solution. Covalently bonded crystals are also very common, notable examples being

diamond, silica, and graphite. Polymer materials generally will form crystalline regions,

but the lengths of the molecules usually prevent complete crystallization. Weak Van der

Waals forces can also play a role in a crystal structure; for example, this type of bonding

loosely holds together the hexagonal-patterned sheets in graphite. Most crystalline

materials have a variety of crystallographic defects. The types and structures of these

defects can have a profound effect on the properties of the materials. Some crystalline

materials may exhibit special electrical properties such as the ferroelectric effect or the

piezoelectric effect [8].

Following are few important piezoelectric types used in various applications

2.7.1 Lead Zirconate Titanate (PZT)

Lead zirconate titanate is a ceramic material that shows a marked piezoelectric

effect compared to other ferroelectric properties. PZT develops a voltage difference

across two of its faces when compressed (This is used for sensor applications), and

physically strained when an external electric field is applied (used for actuators etc). It is

also ferroelectric, in other words, it has a spontaneous polarization which can be reversed

in the presence of an electric field. The lead zirconate titanate is widely used in

polycrystalline (ceramic) from with very high piezoelectric coupling. Depending on the

formula of preparation, PZT materials may have different forms and properties.

Manufacturers of PZT use proprietary formulas for their products [12]. Techniques that

are commonly used for preparing the bulk PZT materials such as (PZT-4, PZT-5) are not

21

suited for micro-fabrication. A number of techniques for preparing PZT films have been

demonstrated, including sputtering, laser ablation, jet molding, and electrostatic spray

deposition [13]. Lead zirconate titanate shows a much greater piezoelectricity effect than

quartz. These can readily be fabricated into variety of shapes and sizes and therefore can

be tailored to a particular application [14].

2.7.2 Barium Titanate

Barium titanate is an oxide of barium and titanium with the chemical formula

BaTiO3. It is a ferroelectric ceramic material, with a photorefractive effect and

piezoelectric properties. It has four structures as a solid, starting with the high

temperature to a low temperature structure. These four structures are cubic, tetragonal,

orthorhombic, and rhombohedral crystal structure. All of the structures exhibit the

ferroelectric effect except for the cubic barium titanate structure. Barium titanate can be

manufactured by sintering of barium carbonate and titanium dioxide, optionally with

other materials for doping. Barium titanate is often mixed with strontium titanate. It has

the appearance of a white powder or transparent crystals and is insoluble in water and

soluble in concentrated sulfuric acid. As a piezoelectric material, it was largely replaced

by lead zirconate titanate, also known as PZT. Barium titanate crystals find use in

nonlinear optics. The material has high beam-coupling gain, and can be operated at

visible and near-infrared wavelengths. It has the highest reflectivity of the materials used

for self pumped phase conjugation (SPPC) applications. It can be used for continuous-

wave for wave mixing with milliwatt-range optical power. Barium titanate mostly used

as a dielectric material for ceramic capacitors, and as a piezoelectric material for

microphones and other transducers [15]

22

2.7.3 Polyvinylidene Fluoride (PVDF)

Polyvinylidene Fluoride, or PVDF is a highly non-reactive and pure thermoplastic

fluoropolymer. PVDF is very expensive; its use is generally reserved for applications

requiring the highest purity, strength, and resistance to solvents, acids, bases and heat.

Compared to other fluoropolymers, it is easier to melt because of its relatively low

melting point.

It is available as piping products, sheet, plate and an insulator for premium wire.

It can be injection molded and welded and is commonly used in the chemical,

semiconductor, medical and defense industries, as well as in lithium ion batteries. When

poled, PVDF is a ferroelectric polymer, exhibiting efficient piezoelectric and pyroelectric

properties. These characteristics make it useful in sensor and battery applications. PVDF

has a glass transition temperature (Tg) of about -350C and is typically 50-60% crystalline.

To give the material its piezoelectric properties, it is mechanically stretched to orient the

molecular chains and then poled under tension. Polyvinylidene Fluoride is a synthetic

floropolymer with monomer chains. It exhibits piezoelectric, pyroelectric and

ferroelectric properties, excellent stability to chemicals, mechanical flexibility and

biocompatibility [16].

2.8 Recent Developments in Piezoelectric Ceramics

There has been a growing interest in recent years in piezoelectric ceramics

materials because of their excellent dielectric, sensing, actuating and efficient process

control applications. Lead zirconate titanate (PZT), barium titanate (BaT1O3), lead

metaniobate (PbNb2O6) and polyvinylidene fluoride (PVDF) polymers are generally

favored as smart sensing materials. These materials are being used in critical engineering

23

systems and smart structures. Fatigue failure due to electrical and thermal shocking is a

major issue in degradation of these materials. A lot of work has been done in this area but

still various issues need to investigate. Recent developments and current issues in

piezoelectric materials and deterioration of their properties in different working

conditions have been discussed in a review paper titled “Recent Developments in

Piezoelectric Ceramics Materials and Deteriorations of their Properties” [Appendix-B].

The new piezoelectric finite element capability available in some commercial packages

like ANSYS makes it convenient to perform static, dynamic, transient and thermal

analysis for the fully coupled piezoelectric and structural response.

In the past two decades many theoretical studies including finite element analysis and

modeling have been conducted to the fracture and damage of piezoelectric ceramics

under electrical, mechanical or combined electromechanical loading modes. The decay of

piezoelectric properties and the degradation mechanisms of piezomaterials due to the

strong coupling effect of the high alternating electric field and mechanical load have been

serious concerns, but have not well characterized. In particular, durability performance of

peizomaterials, in terms of integrity and piezoelectric properties, is always a key issue in

long term for both conventional piezoceramic based actuation system and recently

developed new generation actuation systems. Cyclic domain switching in piezomaterials

caused by the high frequency cyclic electric field and consequently the electric field

induced fatigue crack growth, and the temperature rise due to self heating of the

materials, seriously deteriorate the electromechanical properties of piezomaterials [17].

Ferroelectric ceramics has a broad range of applications due to its enhanced physical

properties such as dielectric coefficients, elastic – optical coefficients, piezoelectric

24

coefficients, elastic coefficient. All these properties have been investigated [18-20].

There are considerable reports on experimental studies of fatigue induced either by an

electrical or a mechanical load alone [21]. Ferroelectric fatigue was a key problem for the

wide application of ferroelectric materials in non-volatile memories and other

electromechanical devices, such as actuator. Up to now, much work has been carried out

on the research towards understanding ferroelectric fatigue and thus many corresponding

mechanisms have been suggested [22].

In the ferroelectrics literature, the term fatigue generally refers to the gradual degradation

of bulk material properties, such as the saturation remnant polarization, in a cyclically

loaded specimen.

Experiments have shown that cracks grow in ferroelectric ceramics under cyclic electric

fields. The works of Jiang, Cross, and coworkers have shown that high porosity might

cause the severe decrease on polarization under alternating electric loading. Jiang et al.

(1993) have found from their experiments that the smaller the grain size the more

difficult it is to produce and propagate cracks. Jiang have studied the difference on the

electric fatigue behavior caused by conditions of ceramic-electrode interfaces [23, 24].

Hill et al. (1996) have used transmission electron microscopy (TEM) to observe the

fatigue behavior of PZT -8 by measuring acoustic velocity and piezoelectric coefficients

[25]. Tai and Kim have investigated the fatigue of PZT ceramics under cyclic

compressive loading by measuring piezoelectric coefficient and capacitance [26].

Recently, Jiang and Sun (1999) have studied the behavior of fatigue crack growth rates

under combined electrical and mechanical loads. They have attempted to use a single

energy parameter to quantify electrical and mechanical loads. They also had extended the

25

mechanical fatigue theory and have included an intensity factor of electric displacement

in the Paris law [27].

It is common practice to embed piezoelectric sensors into prototypes because these

sensors can be manufactured with strength and dimensional characteristics that do not

degrade the structural integrity of the materials of the prototype. When thermal effects are

generated through either friction or direct exposure to significant temperature gradients,

the reliability of the electrode layer in these piezoceramics can completely dominate the

performance of the device being investigated [28]. A new 3-D electromechanical-coupled

field finite method has been proposed to accurately predict the resonant frequency and

harmonic response of a system applying the step voltage as input. The simulation of

piezoelectric devices with time domain was modeled by Lerch (1990) [29].

2.9 Thermal Cycling and Shocking in Piezoelectric

Ceramic materials are brittle and susceptible to catastrophic fail under most

conditions of high heat transfer and rapid environmental temperature variations. Thermal

stress resistance of brittle ceramics can be measured by two methods. The first approach

is based on thermo elastic theory [30]. Material properties are selected to avoid the

initiation of fracture by the thermal stresses. In general this requires materials with high

values of tensile strength, thermal conductivity, and thermal diffusivity combined with

low values of thermal expansion coefficient, Young’s modulus of elasticity, Poisson’s

ratio and emissivity [31-33]. Some workers have reported a reasonable agreement

between calculated and observed thermal stress performance, providing a valid basis for

the thermo-elastic approach to thermal stress fracture [34, 35]. Thermal shock resistance

concerned with the extent of crack propagation and the resulting change in physical

26

behavior of the material. Thermal stress resistance may be determined by the relative

change in strength, the loss of weight, or the change in permeability. The change in

elastic behavior or resonant frequency may also be used as a measure of thermal stress

resistance. A new approach to the calculation of the extent of crack propagation in brittle

ceramics as a function of thermal shock treatment has been presented by

D.P.H.Hasselman (1969) [36].

Heat transfer effects in ferro-electric materials, electric impact loading, thermal effects of

piezoelectric sensors and heat generation rate in piezoelectric materials have also been

investigated. Ningning Dul (2006) investigated the energy dissipation mechanisms and

thermal effects in cracked piezoelectric materials [37]. His results showed that the

temperature rise caused by electric saturation or electric impact loading is remarkable and

may play a significant role in fracture of piezoelectric materials especially under

high frequency condition and some electric-waves with higher electric loading rates.

Many piezoelectric structural components are under the influence of transient thermal

loads like in aerospace structures and hence it is necessary to accurately model the

coupled thermal-mechanical-electrical behaviors of piezoelectric ceramics. In thermal

shock conditions during sudden heating or cooling of a solid, development of high

values of stresses are possible. If the thermal transient is severe enough, sudden fracture

may occur. Thermal shocks in a plate of finite thickness have been attempted. A fracture

mechanics analysis having an edge crack in the transient stress analysis, and the degree

of severity of any given thermal shock is characterized in terms of the stress-intensity

factor [38, 39]. The dynamic linear piezothermoelastic theory, the constitutive

formulations, and governing equations for thermal, elastic, and electric fields have been

27

discussed [40, 41]. The effective thermal expansion and pyroelectric coefficients of

piezoelectric composites have also been analyzed [42]. The transient thermo-electric-

elastic fields in a hexagonal plate were investigated by Choi et al [43]. Recently,

numbers of coupled thermal-mechanical-electrical finite-element method are being used

to study thermally induced stresses in smart structures. The phenomenon of strength

evaluation of piezoelectric ceramics under transient thermal environment has also been

investigated [44].

Piezoelectric thin films operating in many structural components, like in aerospace

component, are sometime subjected to severe thermal loading which may be produced by

aerodynamic heating, by laser irradiation, or by localized intense heating. The amount of

energy delivered to the thin film surface in short time plays a significant role in

developing thermal stresses. Thermal shock and thermal fatigue of ferroelectric thin film

were investigated by the pulsed laser tests by Zheng et al [45]. Micrographs from

scanning electron microscope show a remarkable difference in microstructure and grain

size after during thermal cycling. They also discussed the possible origins of the thermal

fatigue cracks. Thermal shocks in a plate of finite thickness have been attempted.

Thermal shock and thermal fatigue of ferroelectric thin film were investigated by the

pulsed laser tests by X.J.Zheng et. al. (2005)

Lead zirconate titanate decreases the dielectric constant and the resonance frequency by

thermal shock. Temperature stability for dielectric constants and resonance frequencies is

an important phenomenon. Tolerance to thermal shocks is strictly required in piezoelectric

resonators and filters. Resonance frequency of vibration mode has also been investigated

earlier [46].

28

Fatigue studies shows that material degradation is strongly influenced by temperature and

by the electromechanical fatigue. Temperature plays an important role in dictating the

electromechanical response of piezoelectric materials. In typical actuators, the operating

temperature is less than 100C0 and work show that the relative permittivity varies linearly

with temperature up to 120C0 and it shows that linear approximation of relative

permittivity with temperature is valid. Behavior of piezoelectric ceramics used in actuator

application was discussed by Donny Wang and his fellows [47]

The extent of aging has been expressed as total normalized frequency change over a

specific time period. Aging mechanism and high frequency modes of piezoelectric

resonator was earlier analyzed [48].

Thermal shock resistance of the materials was evaluated by water quenching and a

subsequent three point bending test to determine flexure strength degradation. In the

investigation it was analyzed that fracture toughness can be improved. By considering

specific heat treatment the ceramics materials can be shock resistance [49].Transient

thermal analysis of thin strips used in various applications had been investigated since

long. Thin strip with or without crack was determined for its behavior in transient thermal

environment [50].

The ageing process in any ceramic can be accelerated by exposing the ceramic to high

mechanical stress, strong electric depoling field and high temperature approaching the

Curie point. Most of the properties of piezoelectric ceramics changes gradually with time.

The changes tend to be logarithmic with time after poling. The ageing rate of various

properties depends on the ceramic composition and on the way the ceramic is processed

during manufacture. Because of ageing, exact values of various properties such as

29

dielectric constant, coupling, and piezoelectric constants may only be specified for a

standard time after poling. The longer the time period after poling, the more stable the

material becomes.

2.10 Effect of Water and Moistures in Piezoelectric Ceramics

Transient thermal analysis of thin strips has been studied [50]. Piezoelectric thin

films operating in many structural components such as in aerospace applications can

experience severe thermal loading which may be produced by aerodynamic heating, laser

irradiation, or incidental heating from other electrical components. The amount of energy

delivered to the thin film surface in a short time plays a significant role in developing

thermal stresses. Recently Jiang et. al (2006) studied the effect of water induced

degradation on soft PZT piezoelectric ceramics using electromechanical charging in a

NaOH solution. They observed the effect of electrolysis of water on property changes of

the PZT [51]. Other researchers have studied the affect of applying a 50Hz AC voltage on

the degradation in properties of a PZT ceramic ring in NaOH solution. The rings treated

with AC voltage were found to degrade in material properties [52].

As the performance of PZT materials used in various applications may be affected by

changes in temperature and water condition, therefore, in this study the effect on

performance of a PZT material have been analyzed at different frequencies in different

water conditions.

Ceramic materials are brittle and susceptible to catastrophic failure under conditions of

rapid environmental temperature variations [30]. Relative change in strength, the loss of

weight, or the change in permeability, the change in elastic behavior or resonant

30

frequency is the measure of thermal stress resistance [36]. Thermal shocks in a plate of

finite thickness have been attempted. Fatigue studies show that material degradation of

PZT ceramics are strongly influenced by temperature and by the electromechanical

fatigue. Lead zirconate titanate ceramics shows a decrease in dielectric constant and the

resonance frequency when subjected to thermal shock. Thermal shock resistance of the

materials was evaluated by water quenching and a subsequent three point bending test to

determine flexure strength degradation. Degradation of various properties of the piezo

devices in the presence of water & AC voltage was investigated and concluded that water

is an important cause for the degradation of PZT piezoelectric ceramics [52].

Dielectric constant is an important parameter, especially in the piezoelectric device such

as resonators and filters used in the electronic circuits. Impedance is also dependent on the

dielectric constant of the piezoelectric. Currently there is limited data available for the

thermal shocking and quenching effect of a thin PZT disc. Therefore there is a scope to

investigate various parameters which are still unattended. In this research work, the focus

is to investigate the degradation of thin PZT disc due to thermal shocking and its

quenching effect. A noticeable change in capacitance and dielectric constant has been

observed which is further changing other piezoelectric properties.

By considering all of the above discussions, it is concluded that fatigue behavior of

piezoelectric ceramics materials either by electrical, mechanical, electromechanical has

been investigated extensively, whereas there is a scope of work during thermal

cycling/shocking of piezoelectric material in variable conditions. In chapter 4

experimentations performed, analyzed and comprehensive discussions have been

presented.

31

CHAPTER#03

EXPERIMENTAL METHODOLOGIES

3.1 Introduction

The difference between environmental and cyclic induced fatigue is not very well

clear and some ceramics materials show combination of both. Some standard existing

methodologies particularly for mechanical testing have been studied extensively. In the

present work thermal cycling/shocking of thin PZT disc has been experimentally studied

by using relevant instrumentations. Experimental arrangement for this research work has

been briefly described here and will be elaborated in next chapter. Reliability has been

assured by calibration and by repeatability. Calculations of piezoelectric parameters are

based on IEEE standard on Piezoelectricity [53].

This chapter demonstrates the testing methodologies, selection of specimen and design of

experiments. A self designed and fabricated circuitry for the determination of frequency

of maximum and frequency of minimum impedance has also been demonstrated. The

methodology for the determination of elastic, piezoelectric, and dielectric constant has

been done by using resonance method. A brief description of the experimentations phases

performed for this particular research has also been described.

3.2 Standard Fatigue Testing Methodologies

Ceramics and Glasses subjected to static or cyclic loads exhibit time-dependent failure

due to the growth in inherent and induced flaws to a critical size. Cyclic loading is not

required to generate crack extension. Hence some time the phenomenon is also referred

32

to as “static fatigue.” The phenomenon is also referred to as stress corrosion, delayed

failure, slow crack growth or environmentally induced fatigue. In addition to an

environmentally induced, stress corrosion mechanism, many ceramics materials exhibit

enhanced fatigue crack growth during cyclic loading. Factors such as grain size and grain

boundary phase, which generally relate to the toughening or environmental sensitivity,

influence the sensitivity to cyclic loading. Fatigue mechanisms in brittle solids can be

classified as environmentally induced fatigue or as cyclic fatigue. Environmentally

induced, or static, fatigue in ceramics is chemically activated atomic reaction that is

enhanced by stress and temperature [54].

3.3 Thermal Cyclic Loading in Piezoelectric Ceramics

Due to wide range of operating conditions and applications for the systems under

development, careful consideration must be given to the selection of piezoelectric

materials. The selection of material becomes more important when they are used for wide

range of operating temperatures. The current research work is focused to thoroughly

investigate the characteristics of thin PZT disc in various cyclic and shocking

environments. Thermal shock conditions due to sudden heating and cooling of the solids

can develop very high stresses. The effect of these stresses becomes sensitive when the

disc size is too small as selected for the present work. The degree of damage and strength

degradation of ceramics subjected to severe fluctuating thermal environments plays a

significant role in relation to service requirements and lifetime performance. The coming

articles are to demonstrate the selection of specimen, instrumentation and methodologies

for the measurement of few piezoelectric properties.

33

3.4 Selection of Specimen

Thin discs of lead zirconate titanate specimen described in Table.3.1 have been

selected for experimentation, Parent properties of specimen are described in Table.3.2.

PSI-5A4E is an industry type 5A (Navy Type II) piezoceramic. Thin vacuum sputtered

nickel electrodes produce extremely low current leakage and low magnetic permeability.

It operates over a wide temperature range and is relatively temperature insensitive. DOD

TypeII, Lead-Zirconate Titanate having high strain (charge) constants, permittivity, and

coupling constants. Its mechanical quality factor is low with high Curie temperature

which extends its temperature range and thermal stability.

High charge output useful for sensing devices and generator elements.

High strain output useful for large displacements at modest voltages.

The particular selected type is used for sensing devices like, receivers, knock, acoustic,

musical pick-ups, vibration, vortex, material testing and for actuators like valves,

positioning, vibrating, fans, tilters etc.

Table.3.1: Description of Specimen (PSI-5A4E Single Layer Disks) Composition Trade (Dimension)

Diameter Thickness Part No

Lead Zirconate Titanate PiezoSystems Inc. 12.7mm 0.191mm T107-A4E-273

34

Table.3.2 Parent Specimen Properties as provided by supplier (PIEZO SYSTEM INC. USA).

Piezoelectric Properties Sr #

Description Notation Value Units

01 Relative Dielectric Constant @1KHz

KT3 1800

02 Piezoelectric strain coefficient d33 390 x10-12 Meters/Volt 03 d31 -190 x 10-12 Meters/Volt

04 Piezoelectric voltage coefficient g33 24 x 10-3 Volt meters/Newton

05 g31 -11.6 x 10-3 Volt meters/Newton

06 Coupling coefficient K33 0.72 07 k31 0.32 08 Polarization field Ep 2 x 106 Volts /meter 09 Initial depolarization field Ec 5 x 105 Volts/meter Mechanical 10 Density Ρ 7800 Kg/meter3 11 Mechanical Q Q 80 12 Elastic modules YE

3 5.2 x 1010 Newtons/meter2 13 YE

1 6.6 x 1010 Newtons/meter2 Thermal 14 Thermal expansion coefficient ~ 4 x 10-6 Meters/meter oC 15 Curie Temperature 350 oC

3.5 Resonance Method

All electronics materials have their own resonance frequency on which they

resonate. When exited at this resonant frequency, fn, the body will resonate freely with

greater amplitude than at other frequencies. In spite of resonant frequency there is an

anti-resonant frequency, fm, where the impedance of the body is at a maximum and the

oscillation amplitude is at a minimum. The measurement of these characteristics

frequencies provides the means to evaluate the piezoelectric and elastic properties of the

ceramic. There are different modes of vibration of the ceramic, such as thickness or

planar mode and other is extensional or longitudinal mode. The resonant frequency is at

35

the point of minimum impedance and the anti-resonant frequency is at the point of

maximum impedance.

At resonance, a piezoelectric element may be modeled by the equivalent circuit. This

circuit is commonly referred to as Van Dyke’s Model and is recommended by the IEEE

Standard on Piezoelectricity [53]. Resonance must be sufficiently isolated from other

modes to eliminate the effects of any adjacent modes. To assure isolation of the

resonance, sample geometry must be chosen carefully. Fixturing of the sample should not

impose any constraints on the vibration of the ceramic. This can be accomplished by

using a point holder positioned at a node of vibration. Also, all leads should be shielded

up to the contact point as much as possible to avoid any stray capacitances which may

arise. Several circuits to measure fm and fn of piezoelectric ceramic have been proposed

[55-57]. The dielectric properties of a piezoelectric vibrator are dependent on the elastic,

piezoelectric and dielectric constant. The above stated properties can be measured by

using suitable size and shape of the specimen is specific orientation. The measurements

are basically consists of determining the electrical impedance of the resonator as a

function of frequency. In particular capacitance of the selected specimen has been

determined at resonance and anti resonance frequencies and respectively the change in

dielectric constant and coupling factor has also been measured.

3.5.1 Measurement of Material Properties

Measurements of capacitance are usually carried out at 1 KHz and at low

excitation voltages (mV level). Although research has shown capacitance and loss to vary

with excitation voltage and frequency [58, 59], the 1KHz, low voltage measurement is

36

used in the determination of material properties. The free relative dielectric constant, K3T,

is defined as the ratio of the permittivity of the material to the permittivity of free space.

It is calculated from the following equations [53, 55]. Equation 3.1 is the measure of

dielectric constant of the material.

TK3 = A

tC0ε

(3.1)

Where t is the distance between electrodes in meters, C is the capacitance in farads, ε0 is

the permittivity of free space (8.85 x 10-12 F/m), and A is the area of an electrode in

meters2.

The loss tangent, tanδ, is defined as the ratio of resistance to reactance in the parallel

equivalent circuit. It is a measure of the dielectric losses in the material and therefore also

a measure of the heat generation capacity of the ceramic when operated under dynamic

conditions. This is a direct measurement and is usually formed at the same conditions as

the capacitance measurement.

The three most common coupling coefficients are kp, k31, and k33; where the p is for

planar, and the 31 and 33 subscripts are for length extensional and thickness extensional

modes. The coefficients k33 and k31 can be calculated from the frequencies of minimum

and maximum impedance by using the equations 3.2 &3.3.

−+

−

−+

=

m

mn

m

mn

m

mn

fff

fff

fff

K)(

1

2)(

tan)(

1

2233

ππ

(3.2)

37

=231K

ψψ+1

(3.3)

Where

ψ =

−+

m

mn

fff1

2π tan ( )

−

m

mn

fff

2π (3.4)

The planar coupling coefficient kp (Eq 3.5) is defined for thin discs and can be

approximated by.

2

22

n

mnp f

ffK −= (3.5)

Elastic compliance is the ratio of a material’s change in dimensions (strain) in relation to

an externally applied load (stress). This is the inverse of Young’s modulus. For a

piezoelectric material, the compliance depends on whether the strain is parallel or

perpendicular to the poling axis and the electrical boundary conditions. Elastic constants

are calculated from the following equations 3.6, 3.7, 3.8, &3.9.

2233 41

lfS

n

D

ρ= (3.6)

233

3333 1 K

SSD

E

−= (3.7)

2211 41

wfS

m

E

ρ= (3.8)

38

ED SS 1111 = ( )2311 K− (3.9)

Where ρ is the density of the material in kg/m3 and l is the distance between electrodes

and w is the width of the ceramic. The superscripts D and E stand for constant electric

displacement (open circuit) and constant electric field (short circuit) respectively.

The dij piezoelectric constants, which relate the applied electric field to the strain, can be

calculated from the coupling, elastic coefficients and the dielectric constant.

The gij piezoelectric constants are related to the dij coefficients and can be measured by

equations 3.10, 3.11, 3.12, &3.13.

ET SKKd 33303333 ε= (3.10)

ET SKKd 11303131 ε= (3.11)

TKdg

30

3333 ε

= (3.12)

TKdg

30

3131 ε

= (3.13)

It should be noted that the piezoelectric coefficients calculated above are only valid at

frequencies well below resonance and do not account for any non-linear behavior of the

ceramic.

39

The mechanical QM, the ratio of reactance to resistance in the series equivalent circuit is

given by equation 3.14.

−

= 22

2

21

mn

n

mmM ff

fCZf

Qπ

(3.14)

The familiar dielectric, elastic, and Piezoelectric constants for Piezoelectric ceramics may

readily be measured employing the proposed experimental setup by finding the minimum

and maximum frequencies.

3.5.2 Density Calculation

The density in Kilograms/ meter3 can be calculated, if required by using the

relationship as under.

Density ρ = weight in Kilograms/volume in m3

ρ = mass in air in Kilograms/(weight in air- weight in water) in Kilograms

3.5.3 Calculation of Free Relative Dielectric Constant K3T

In this work dielectric constant was measured by using the value of capacitance in pF and

physical dimensions of the specimen by using Equation 3.1.

KT3 = Distance between electrodes (m) x C (pF)/Area of one electrode (m2) x 8.85

3.5.4 Calculation of Coupling

Coupling is calculated from the frequencies of minimum and maximum

impedances. The frequencies of minimum and maximum impedances are not the exact

40

frequencies required for these calculations, and a small correction theoretically should be

made. However, when dealing with Barium Titanate and Lead Zirconate-Lead Titanate

compositions, the error resulting from omitting the correction is not significant, and

therefore can be ignored here.

3.6 Determination of Elastic, Piezoelectric, and Dielectric Constants

The elastic, piezoelectric, and dielectric properties of a piezoelectric material are

characterized by knowledge of the fundamental constants referred to a rectangular

coordinate system fixed relative to the crystallographic axes. A determination of these

fundamental constants requires a series of measurements on samples of various

orientations. There are a number of specific sample geometries and experimental

techniques that one can use to make the measurements. The choice of which techniques

to employ is subject to many considerations such as the size and shape of samples and the

instrumentation available. It is therefore not desirable to specify a single technique for

measuring piezoelectric materials. The quantities actually measured nevertheless must be

related to the fundamental elastic, piezoelectric, and dielectric constants by procedures

that are theoretically sound [53]

3.7 Selection of Experimental Setup/ Design of Experimentation

Complete experimental setup to perform experimentations was required. Experimentation

was designed by considering the size and shape of the specimen. Another consideration was to

consider the available experimental facilities for testing and measuring. Experimentation was

designed for thermal cycling and shocking conditions to analyze various effects and

characteristics of the selected specimen.

41

The research work divided into three phases and different instrumentations for testing and

measurements were selected. Care must be taken in the reliability of the instruments and their

functioning.

Instrumentation used for current research work has been listed below. The purpose was to

investigate the real time performance of piezo disc in different water conditions at

variable parameters, investigating thermal shocking effect in de-ionized water from

different temperature differences and at variable frequencies and resistances.

3.7.1 Phase-1: Performance of PZT and its Effect due to Water.

1. Function generator.

2. Oscilloscope.

3. Decade resistance box.

4. Hot plate.

5. Thermometer.

6. pH value measuring meter.

3.7.2 Phase-2 Thermal Cycling/Shocking Effect of Thin PZT Disc

1. Thermal chamber.

2. Thermocouple

3. Impedance analyzer

4. Capacitance measuring test fixture

5. Connecting wires and other accessories.

42

3.7.3 Phase-3 Thermal Cyclic Effect. (At Variable Frequencies and Resistances)

1. Function generator.

2. Oscilloscope.

3. Decade resistance box.

4. Thermal chamber.

5. Thermocouple

3.8 Research Contribution

The required experimentation has been done in three phases and briefly described

in under headings. Detailed description of experimental setup, experimentation and

analysis of results of each phase has been elaborated in chapter 4.

3.8.1 Phase-1: Performance of PZT Disc and its Effect Due to Water.

To understand the philosophy of thin PZT disc in hot water environment and its effect on

output Peak-Peak voltage has been analyzed. The experimentation was designed

accordingly.

This phase performed in three different water conditions as under.

• In simple water

• In de-ionized water

• In NaCl solution

3.8.2 Phase-2: Thermal Cycling/Shocking Effect of Thin PZT Disc

• Thermal shocking from 1000C from thermal chamber to de-ionized water

at 200C.

43

• Thermal cycling test between 1000C and 900C for 60 cycles in step of 10

cycles.

• Thermal cycling test between 1000C and 900C for 60 cycles continuous.

• Thermal shocking from 1500C from thermal chamber to de-ionized water

at 200C.

3.8.3 Phase-3: Thermal Cyclic Effect. (At Variable Frequencies and Resistances)

• At room temperature (200C)

• At 1600C

3.9 Measurements

Phase-1 contributes in determining the output voltage across thin PZT soldered

disc, which determine its sensitivity of output voltage in water due to temperature change

and its effect with respect to variable frequencies and resistances. In phase-1

experimentation, soldered disc was connected with designed circuitry to have the output

peak-to-peak voltage for four selected frequencies. In this part of work, output

performance in the form of Pk-Pk voltage and its effect on thin disc was determined.

Detail will be described in Chapter-4

Phase-2 comprises a comprehensive analysis of cyclic and shocking of PZT thin disc in

thermal environment. By using the experimental results, piezoelectric, mechanical and

physical parameters can be calculated by using the appropriate relationships. In this phase

disc was thermally cycled for specific temperature range and shocked in de-ionized

water. Detail will be described in Chapter-4. Focus of this part of work is only to

determine the change in coupling factor, dielectric constant, and impedance during

44

thermal cycling and shocking of lead zirconate titanate ceramics disc. Due to very small

size of the specimen, the effect of density is supposed to be negligible and therefore not

considered in the calculations.

Phase 3 experimentation was performed in thermal chamber environment. The effect of

temperature with respect to variable frequencies and resistances on its output peak-peak

voltage was analyzed. This part demonstrates the sensitivity of the disc by changing the

above variables in thermal environment. Detailed analysis has been demonstrated in

chapter 4.

3.10 Capacitance measurement by 6451B Dielectric Test Fixture

Dielectric test fixture was attached with impedance analyzer to measure various

parameters during thermal cycling and shocking of PZT disc.

3.10.1 Specifications

These specifications are the performance standards and limits against which the selected

instrument is tested. The function of the fixture is to measure the dielectric constant and

dissipation factor without connecting the solid materials to the unknown terminals. The

specifications are as under.

Frequency range ≤ 15 MHz

Applicable voltage range ± 42 V peak max

Cable length = 1m

Operating temperature 00C to 550C

Operating Humidity ≤ 95% RH (400 C)

Weight = 3.7 Kg (Including accessories)

45

3.10.2 Performance Characteristics

Accuracy of performance characteristics vary with measurement conditions. However

16451B can measure dielectric constant in the range of 1 to 200,000 with an accuracy of

±1% and dissipation factor from 0.000001 to 9.99999 with an accuracy ± (5% + 0.005)

3.10.3 Selection of Electrodes

Four different types and sizes of guarded/guard electrodes are available with the

instrument kit. The selection of these electrodes for measurements depends on the size of

the specimen and measuring condition. Table 3.3 describes the dimensions and function

of the electrodes.

Table 3.3 Description of various electrodes and their selection

Sr # Electrode Description

01 Electrode-A Guarded/guard electrode with 38mm diameter used to

measure a material without thin film electrode.

02 Electrode-B Guarded/guard electrode with 5mm diameter used to

measure a material without thin film electrode.

03 Electrode-C

(For large thin film

electrodes)

Electrode used to measure a material which already have

thin film electrodes applied and consists of a guarded/guard

electrode.

04 Electrode-D

(For small thin film

electrodes)

Electrode used to measure a material which already have

thin film electrodes applied and consists of a guarded/guard

electrode.

46

3.10.4 Operation

The 16451B fixture assembly is equipped with a 4-terminal pair cable assembly,

guarded/guard electrodes, and a micrometer to set the distance between the electrodes. It

is recommended that large knob of micrometer should not be used to bring the

guarded/guard electrode into contact with the unguarded electrode or test material.

Dielectric measurement basically obtained by measuring the capacitance of a solid test

material. Three measurement methods are used by the instrument but we used the

contacting electrode method with thin film electrode. Suitable test material and suitable

electrode is necessary for accurate results.

3.10.5 Contacting Electrode Method (Used with thin film electrode)

This method uses thin film electrode applied on the test materials. Contacting electrode

method with thin film electrodes can be used for those materials on which thin film

electrode can be applied without changing its characteristics. This method is relatively

simple and uses simple equation to calculate dielectric constant. Error caused by air gap

between the electrode and surface of the test material is less in this case. The 16451B

provides two applicable electrodes, Electrode-C and Electrode-D for contacting electrode

method for thin film electrode with respect to size of the test materials.

3.10.6 Testing Material

To eliminate the error in measuring dielectric constant, the specimen should be according

the dimensions as specified by the testing equipment. The shape of the test material for

the 16451B should be a plate or a film. The applicable size of the test material should be

greater than the inner diameter of the guard electrode. It is recommended not to measure

47

a material whose diameter is much greater than the unguarded electrode. Doing this can

overload electrode and may damage it. To get accurate and better results, it is better to

use larger diameter and thinner thickness of the test material. Thickness of test material

should be accurate to get accurate results. Thickness of testing material is limited up to

10mm. The surface of the test material must be flat at all point. Thin film electrodes can

reduce the air gap between an electrode and a test material. Therefore the air film error

using thin film electrodes is less than one using rigid metal electrodes.

3.10.7 Error Corrections

To reduce the residual impedance and to measure the accurate dielectric constant, error

correction needed with the text fixture. For this purpose open and short corrections are

performed. For thin film electrodes, short correction is performed using electrode-C and

electrode-D. Load correction is performed to reduce error, such as negative dissipation

factor that can not be reduced by open and short correction.

3.10.8 Electrode Adjustment

Electrode adjustment of guarded/guard electrode is also necessary for accurate

measurement to check electrode parallelism. There are two types of adjustments, one is

rough adjustment that visually adjusts the electrode and the other is an accurate

adjustment that electrically adjusts the electrode using an LCR meter.

3.10.9 Measurement Procedure

Following steps are performed for the measurement.

1. Select the appropriate size and shape of the specimen with thin film electrodes.

2. Connect the text fixture to the impedance analyzer.

3. Set up the instrument to measure capacitance and dissipation factor (Cp-D)

48

4. If changing electrodes, perform the adjustment of electrode as described earlier.

5. Perform an open and short correction.

6. Set the test material between the electrodes.

7. Measured values of Cp and D by impedance analyzer will be used in the following

equations to calculate dielectric constant and dissipation factor.

rε =0.

.εACt pa

Where

Cp Equivalent parallel capacitance [F]

D Dissipation factor

ta Average thickness of test material [m]

A Area of guarded electrode [m2]

εo = 8.854 x 10-12 [F/m]

εr Dielectric constant of test material

It is recommended that measure three or more reading for take average for

reliability and accuracy.

3.11 Designed Circuitry for Frequency Determination

Experimental determination of frequency of maximum and minimum impedance

was one of the major parts of the research. Provision of an appropriate experimental

arrangement was a challenging job at local university and even there was no provision to

do required experimentation in any other organization. After having a comprehensive

literature review it was decided to have our own set up for the determination of frequency

49

of maximum and minimum impedance. A low cost experimental arrangement was

designed and fabricated [61]. A wave form signal generator has been used for the

generation of signals along with the designed circuitry.

The main parts of this setup are:

1. Switch box circuit 2. Oscillator circuit 3. Frequency counter 4. Decade resistor circuit 5. Voltmeter 6. Waveform generator

Fig.3.1 shows the designed circuit along with the connectors to measure the required parameters.

Fig-3.1 Self designed circuitry for the determination of fm and fn consisting of Switch box circuit, Oscillator Circuit & Decade resistor circuit

3.11.1 Switch Box Circuit

The circuit described in Fig.3.2 plays a central role in determining the desired

frequencies of maximum and minimum impedance. It has two types of selection

switches. Path control switch SW1 and the load resistance select switch SW2. Path

control switch SW1 is made by using a DPDT (Double pole double through switch). The

50

switch contains two sets of contacts that can be switched to connect to either of two

positions.

This switch selects one of the two paths i.e.. Specimen selection path and the decade

resistor path. When the switch is moved down then it selects specimen in the

measurement circuit. When the switch is moved up then it selects decade resistor in the

measurement circuit. The switch connects neither specimen nor decade resistor when it is

in the middle position.

Fig.3.2 Switch Box Circuit to determine the frequencies of maximum and frequency

of minimum impedance.

The switch box has an input signal which comes from the Oscillator card by using a

coaxial cable. Coaxial cable has a single copper conductor at its center. A plastic layer

provides insulation between the center conductor and a braided metal shield. The metal

shield helps to block any outside interference from fluorescent lights, motors, and other

components. In this case the coaxial cable is used instead of the normal two wire cable to

prevent undesired signal addition to the measurement circuit as this type of cable avoids

the signal attenuation due to the shielding present outside the copper connector. This

cable has another special addition which is made for the protection of the measurement

51

signal which is 100 ohms resistance connected at the input side of the cable. This resistor

limits the high values of current from flowing through the measurement circuit. Also

along with the 1 ohm resistor it forms a voltage divider circuit to increase the circuit

sensitivity.

Load resistance control switch SW2 is made in this circuit by using a 10- way position

switch. This switch can select any one of the nine resistance connected to the main

circuit. If the select position knob of any position is at the bottom level then the resistance

in that path is out of the main circuit while if the position knob is at the top level then that

path resistance would be entered into the main circuit as a load resistor. There are nine

different resistances available. Any one of these can be selected but only one value at a

time (Table 3.4).

Table. 3.4 Selection of Resistance in Switch-2 SW2 position 1 2 3 4 5 6 7 8 9

Resistor Value (ohms)

1 3.3 10 33 100 330 1000 3300 10000

Output signal from the main circuit is connected to a Voltmeter through a coaxial cable.

Again in this case coaxial cable is used for accurate measurements and fast data transfer.

This cable has no resistor as were placed in the input coaxial cable because to avoid any

loading effect to the coming measuring device i.e.. Multimeter. Loading effect reduces

the signal magnitude if there is a resistance comparable to the value of the voltmeter at

the output stage of the measuring setup. Both the input and output coaxial cables are

connected to the switch box circuit card by means of PCB mounted coaxial cable

connector. This is the most common type of connector used with coaxial cables and is

called the Bayone-Neill-Concelman (BNC) connector

52

Two 2-pin terminal blocks are also present in the switch box circuit. One terminal block

is for connecting the specimen to the switch box circuit and the other is for connecting

the decade resistor.

3.11.2 Oscillator Circuit

This circuit (Fig. 3.3) is made to produce a frequency signal of very low distortion in the

range of 10 to 200 KHz. Its design is based on the classic 555 timer circuit. It requires a

DC supply of more than 9 V to produce the required frequency signal. A three pin

terminal block is meant for connecting the DC supply with the correct polarities,

as indicated on the terminal block pins. To adjust the frequency of the oscillator circuit a

multiturn POT is used. When this POT is rotated in the clockwise direction, the

frequency of the signal increases while on rotating it counter clock wise decreases the

signal frequency. A 2-pin terminal block is present in the oscillator card to connect the

required frequency signal to the external setup.

Fig.3.3 Oscillator Circuit (frequency signal range10 to 200 KHz)

53

3.11.3 Frequency Counter

To measure the frequency produced by the oscillator circuit a frequency counter is

required. In this setup a very precise digital Multimeter with the frequency measuring

capability is used. For determining the frequency of counter circuit the positive (red) lead

of this digital Multimeter is connected to the positive (+) pin of the signal terminal block

at the oscillator card while the negative (black) lead of the digital Multimeter is

connected to the negative (-) pin of the same signal terminal block. While the position

selection switch of the Multimeter is positioned at the Hz position.

3.11.4 Decade Resistor Circuit

The decade resistor circuit box (Fig.3.4) is made to get precise resistor values

from 1 ohm to 111ohms. This circuit has two 10-way position selection switches which

are named as switch I and switch II. In switch I, we can have a resistor value from 1 ohm

to 10 ohms.

54

Fig.3.4. Decade resistor circuit Fig.3.5. Waveform Generator

The scheme of selection is that if the switch knob of any of the position is at the top level

then that resistor value will be selected and if the knob is at the bottom level then that

resistor will be out of the selection. But we can select only one position at a time. There is

also a three position selection switch which can select any of the two resistor values as

obtained from the switches I and II as in Table 3.5. While this switch is at the middle

position nothing is selected

Table.3.5 Selection of Resistance for Switch I & Switch II Switch I top position

1 2 3 4 5 6 7 8 9 10

Resistor value (ohms)

1 2 3 4 5 6 7 8 9 10

Switch II top position

1 2 3 4 5 6 7 8 9 10

Resistor value (ohms)

11 22 33 44 55 66 77 88 99 110

55

3.11.5 Waveform Generator

The waveform generator selected for the above stated setup is “Tektronics AFG

3021”, which is a 25 MHz single channel arbitrary waveform generator shown in Fig.3.5

having capability 1 mHz to 25 MHz Sine Waveform

3.11.6 Voltmeter A very sensitive digital Multimeter is used as a voltmeter in this setup for

determining a sharp change of the voltage values. The setup is completed to find out the

frequency of minimum impedance and the frequency of maximum impedance.

3.11.7 Frequency Measuring Procedure

1. Apply a waveform with waveform generator.

2. Turn switch 1 of the ‘switch box circuit’ to specimen.

3. Set switch 2 to 1 ohm i.e.. switch 2’s position 1 to ON and the remaining

positions 2 to 10 to OFF.

4. Set the waveform generator as:

Run Mode: Continuous

Function : Sine

Peak-to-peak output voltage: 5V

Channel: ON

Output: connected to the switch box using a coaxial cable

5. Slowly increase the frequency on the waveform generator from 1 Hz (i.e.. 1

Cycle/sec) to a value where a sharp maximum increase in voltage is obtained on

the ‘digital voltmeter’. If this sharp increase is not obtained then it will be

56

required to gradually increase the resistance from switch 2 i.e.. select position 2 to

ON and remaining 9 positions to OFF for selecting 3.3 ohms resistance and then

increase the frequency of waveform generator as described above. If the sharp

increase is not obtained then we will have to increase the resistance to 10, 33 or

100 ohms by selecting the corresponding switch 2 position to ON and the

remaining 9 positions to OFF. It is noted here that use the minimum possible

resistance to get the required change. In this way the frequency at which a sharp

increase in voltage is obtained will be the frequency of minimum impedance ‘fn’.

Read this value from the display of the waveform generator.

6. Now turn switch 2 to 1000 ohms i.e.. switch 2’s position 7 to ON and the

remaining 9 positions to OFF. Slowly increase the frequency from 1 Hz (i.e.. 1

Cycle/sec) to a value where a sharp decrease in voltage is obtained on the ‘digital

voltmeter’. If this sharp decrease is not obtained then it will be required to

gradually increase the resistance using switch 2 from 1000 ohms to 10000 ohms

then increase the frequency of waveform generator as described above. Again it is

required to get the desired response with the minimum possible selected

resistance. In this way the frequency at which a sharp decrease in voltage is

obtained will be the frequency of maximum impedance ‘fm’. Read this value from

the display of the waveform generator

An effort has been made to measure the frequency in the piezoelectric materials.

Development of a low cost experimental setup can be used for the demonstration to the

new researcher interested in this field. Fatigue behavior of piezoelectric ceramics

57

materials under various conditions definitely deteriorates the piezoelectric properties and

therefore the proposed setup is one of the basic needs to calculate frequency at maximum

and minimum impedance which are further used for calculating the other piezoelectric

parameters.

3.12 Measurement and Effect of Thickness by ANSYS

One of the most popular finite element software package ANSYS has the capabilities to

perform coupled field analysis. Piezoelectric materials can be simulated for their

particular geometry especially in this case the importance is to analyze the effect of

thickness for out put voltage with respect to load. The modeling, analyzing of these smart

scale components remained always a challenging job. A small effort in this regard has

been analyzed to determine the thickness effect in piezoelectric beam.A piezoelectric

cantilever beam analyzed for different thicknesses. Voltage change in each electrode

along with other related properties/parameters were found. Thickness variation produced

remarkable important results which can be used for optimizing the thickness range in

these smart materials. Voltage percentage per electrode determined and different nodal

solutions were obtained. Various recommendations have been suggested to analyze such

smart material before using in various applications for the generation and actuation

systems and for their reliability and durability [62] .

This chapter was all about the methodology adopted and about the instrumentation used

during experimentation. The self designed circuitry was an effort to design and fabricate

a low cost measuring instrumentation required for the frequencies determination. Due to

short range of this designed circuitry, the further experimentation has been performed by

using the instrumentation described earlier. in article 3.7.

58

CHAPTER # 04

EXPERIMENTATIONS AND ANALYSIS OF RESULTS

4.1 Introduction

Degradation in thin piezoelectric specimens occurs due to various cyclic loadings.

Such degradations may alter piezoelectric properties of materials. In chapter 3 the

research methodologies and brief description of experimentations was presented, whereas

the detailed experimentation, analysis of results and discussions has been elaborates in

the present chapter. Experimentations were performed in three different phases described

briefly in chapter 3. The aim of the experimentation was to observe that how

temperature/environment and medium influences the electrical and piezoelectric

properties of such thin piezoelectric specimens. It was observed that thermal cycling/

shocking affecting some critical characteristics of the material. These properties

definitely affect the performance of these materials. Various experimental phases have

been described below.

4.2 Phase-1: Performance Characteristics of a Lead Zirconate

Titanate Piezoelectric Ceramic Disc in Water.

Piezoelectric materials used in various sensing and actuating devices where they

may face various environmental conditions like moisture, and water. Degradation in

59

piezoelectric materials properties due to extensive electrical and thermal cycling is a

common phenomenon, which some time alter their internal characteristics. The

degradation in properties can affect the function and efficiency of instruments in which

these materials are being used. Therefore, it becomes important to identify the extent of

changes in performance when exposed to different types of solutions. A piezoelectric

ceramic disc was exposed to 3 different solutions, ordinary water, de-ionized water and a

solution of NaCl. The PZT was immersed in these solutions at 800C and performance

characteristics recorded on different frequencies. After effects of the immersed disc due

to three different solutions have been analyzed and it is observes that the PZT ceramic is

sensitive to the type of water, but regains its original performance characteristics within

short period of time. Out put peak-peak voltage is the performance parameter. In most of

the practical applications, the performances of piezoelectric materials are temperature and

frequency dependent. The intensity of temperature may change its internal characteristics

temporarily or permanently. Lead zirconate titanate (PZT) based ceramics are widely

used for their piezoelectric properties and these properties may degrade due to the

application of mechanical, electrical, electromechanical, and thermal cycling. A lot of

work is being carried out in exploring the behavior of these smart materials in electrical

and electromechanical loading conditions. Depolarization is one of the sources of

degradation, usually in those devices which undergoes a temperature rise during

operation. Performance of piezoelectric materials are affected by environmental factors,

including temperature, pressure, and humidity. It has been reported that the life time of

the piezoelectric devices decreases with the increase in temperature and humidity [63]. It

has been found that water facilitates the electro migration of silver electrodes along the

60

grain boundaries of piezoelectric ceramics [64]. Other studies showed that water

influences and causes of degradation in the presence of electricity [65]. In most practical

applications, the performance of thin PZT disc is dependent on temperature. The intensity

of temperature may change its characteristics permanently or it affect temporarily. For

this reason the temperature rise levels should be taken into consideration and studied in

depth [66].

Piezoelectric thin films operating in many structural components such as in aerospace

applications can experience severe thermal loading which may be produced by

aerodynamic heating, laser irradiation, or incidental heating from other electrical

components. The amount of energy delivered to the thin film surface in a short time plays

a significant role in developing thermal stresses. Thermal shock and thermal fatigue of

ferroelectric thin films were investigated by pulsed laser tests by Zheng et. al [67]. Water

induced degradation in lead zirconate titanate piezoelectric ceramics was studied before by

W.P.Chen et. al [68]. In 1996, Y.C.Chan et. al. [69] found that a thin water film can form

on the surface of ceramic components by condensation of aqueous vapor in air. In the

presence of voltage on such thin water film may cause degradation in piezo properties.

PZT materials are frequency and temperature dependent and it is observed that there is

slight decrease in the dielectric constant with the increase in frequency. Effect of

temperature and frequency on dielectric and ferroelectric properties has been investigated

[70]. Recently Jiang et. al studied the effect of water induced degradation on soft PZT

piezoelectric ceramics using electromechanical charging in a NaOH solution. They

observed the effect of electrolysis of water on property changes of the PZT [71]. Other

researchers have studied the affect of applying a 50Hz AC voltage on the degradation in

61

properties of a PZT ceramic ring in NaOH solution. The rings treated with AC voltage

were found to degrade in material properties [72]. Effect of heating rate on dielectric and

pyroelectric properties of PZT has been investigated by Mohiddon, et al. [73]. Other

researchers have studied the affect of applying a 50Hz AC voltage on the degradation in

properties of a PZT ceramic ring in NaOH solution. The rings treated with AC voltage

were found to degrade in material properties [74]. Effect of liquid in thin piezoelectric

plates has been studied earlier [75].

PZT instruments used in many environmental conditions and mediums like air, water, and

other chemical environments. The focus in this phase is to investigate the behavior of thin

disc in different water conditions at a temperature where it is under some excitation at

variable frequencies. Aftereffect of the water containments on the output peak-peak

voltage has been analyzed. The aim was to investigate the effect of water particles those

adhere to the surface of the disc on its performance characteristics.

4.2.1 Piezoelectric Material.

A piezoelectric single layer disc described in Table.3.1 was used for

experimentation. The disc was nickel electroded on its major faces and two wires were

soldered by using the compatible solder and flux. The parent properties of the

piezoelectric disc are described in Table.3.2.

62

4.2.2 Test Setup and Variables.

The tests were conducted in normal tap water having a pH value of 8.17, de-

ionized water having a pH value of 7.63 and in NaCl solution. A 5mg 99.5% pure sodium

chloride by Fluka Chemika was dissolved in 20ml de-ionized water to prepare a solution.

The water was placed in a container and heated by using a hot plate and approximately

kept constant at about 80oC with a variation of temperature ±1oC. The PZT specimen was

attached to an electric circuit consisting of function generator, decade resistor and

oscilloscope. The frequency input was developed by WAVETEK Model 273, 12 MHz

programmable sweep/function generator. The output peak-to-peak voltage was observed

by Tektronix TDS210 digital real time oscilloscope. The experimental setup is shown in

Fig-4.1.

Oscilloscope Decade Resistor Box

Computer Function Generator

Sample

Fig.4.1 Schematic Arrangement for the determination of Pk-Pk Voltage at variable frequencies

63

Output voltages were measured using four different frequencies generated by the function

generator. The selected frequencies were 50,100,150 and 200 Hz. The voltage across

Channel-1 and Channel-2 was 5Volts and 2Volts respectively and kept constant for all

measurements. A constant resistance of 110KΩ was selected from the decade resistance

box. Initial trend for output (peak- to-peak voltage) for selected frequencies measured in

air is shown in Fig-4.2. For this particular range of frequency input, the output voltage is

going to decrease.

5.32

8.48

7.46.28

0123456789

0 50 100 150 200 250Frequency (Hz)

Pk-P

k V

olta

ge (V

)

Fig-4.2. Variation of peak to peak voltage as a function of frequency.

First series of experimentation was performed in ordinary tap water with the frequency

set at 50 Hz and its corresponding output voltage in real time was observed by

oscilloscope and recorded. When the specimen was placed in hot water, its frequency

sharply decreased from 6.4V to 400mV. The PZT ceramic disc was placed in water at a

temperature of 80oC for 5 minutes and then taken out. The peak-to-peak voltage of the

64

PZT in air at room temperature 20oC was recorded and after the disc was immersed again

in the medium. Total ten such cycles were performed for each frequency (50, 100, 150

and 200 Hz). The total time for which the disc was immersed in water was about 50

minutes. This experimentation was repeated for de-ionized water and for the NaCl

solution. De-ionized water is similar to distilled water, in that it is useful for scientific

experiments where the presence of impurities may be undesirable. The lack of ions

causes the resistivity of water to increase. Ultra-pure de-ionized water can have a

theoretical maximum resistivity up to 18.31 MΩ·cm, compared to around 15 kΩ·cm for

common tap water. Further investigations were carried out to observe the after effects of

water on the peak to peak voltage with respect to time. After having the PZT disc to ten

thermal cycles for each frequency, the disc was placed in a vertical direction and allowed

to cool in still air at room temperature and a real time data was directly recorded for each

minute until the PZT surfaces were completely dry and the maximum output voltage at

particular frequency was obtained.

4.2.3 Results and Discussion

The response of the PZT ceramic during the heating and cooling (i.e. drying time)

of samples has been tabulated in Tables 4.1 to 4.17 and trends have been shown in Figs

4.3 to 4.8. The change in peak to peak potential values when the PZT ceramic was taken

out from water as a function of different frequencies, and when completely dried have

been shown in these figures. Tables 4.1 to 4.4 comprise the data obtained per minute for

heating cycle at 50, 100, 150 and 200 Hz frequencies in simple tap water. Values in each

case are taken twice and an average value has been considered for further discussion and

65

analysis. In general, the trend for peak to peak potential values recorded for the PZT.

When disc instantly taken out from ordinary water, de-ionized water and NaCl solution it

shows decrease in its original peak-peak values. The drop in potential in ordinary water

was different for the drop in other two water conditions. The drop in voltage is also

frequency dependent and clearly shown in Fig.4.3, Fig.4.5, and Fig.4.7.

Table 4.1 Heating time in ordinary water and respective voltage at 50Hz

Sr # H.T(Min) Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk 1 0 8.48 8.56 8.52 2 5 3.52 4.06 3.79 3 10 3.12 3.28 3.2 4 15 2.48 2.72 2.6 5 20 2.56 2.88 2.72 6 25 2.32 2.48 2.4 7 30 2.16 2.24 2.2 8 35 2.08 2.16 2.12 9 40 2 1.92 1.96 10 45 1.84 2 1.92


Sr # H.T(Min) Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk 1 0 7.44 7.52 7.48 2 5 2.32 2.48 2.4 3 10 2.16 2.24 2.2 4 15 2.16 2.32 2.24 5 20 2 2.08 2.04 6 25 1.92 2 1.96 7 30 1.76 1.82 1.79 8 35 1.84 1.92 1.88 9 40 1.76 1.92 1.84 10 45 1.76 1.84 1.8

66


Sr # H.T(Min) Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk

1 0 6.24 6.4 6.32 2 5 1.92 2.08 2 3 10 1.92 2.16 2.04 4 15 1.76 1.84 1.8 5 20 1.6 1.68 1.64 6 25 1.6 1.76 1.68 7 30 1.6 1.76 1.68 8 35 1.6 1.68 1.64 9 40 1.6 1.68 1.64 10 45 1.6 1.52 1.56


Sr # H.T(Min) Pk-Pk (V) Pk-Pk (V) AvgPk-Pk 1 0 5.36 5.44 5.4 2 5 1.76 1.84 1.8 3 10 1.92 1.84 1.88 4 15 1.68 1.76 1.72 5 20 1.6 1.76 1.68 6 25 1.6 1.68 1.64 7 30 1.6 1.68 1.64 8 35 1.36 1.6 1.48 9 40 1.44 1.52 1.48 10 45 1.6 1.68 1.64

Table 4.5 Drying Time after taking out from ordinary water at 50Hz

Sr # Time(Min) Pk-Pk(V) Pk-Pk(V) Avg Pk-Pk 1 0 1.84 2 1.92 2 1 1.64 1.84 1.74 3 2 1.76 1.92 1.84 4 6 1.92 2 1.96 5 8 1.6 1.68 1.64 6 10 1.52 1.6 1.56 7 12 7.8 8 7.9 8 13 8.12 8.24 8.18 9 14 8.48 8.56 8.52 10 15 8.48 8.56 8.52 11 16 8.48 8.56 8.52

67


Sr # Time(Min) Pk-Pk(V) Pk-Pk(V) Avg Pk-Pk 1 0 1.84 1.92 1.88 2 2 2 2.08 2.04 3 4 1.68 1.76 1.72 4 6 1.6 1.68 1.64 5 8 1.52 1.6 1.56 6 10 2.08 2.16 2.12 7 12 4 4.32 4.16 8 13 7.36 7.44 7.4 9 14 7.44 7.52 7.48 10 15 7.44 7.52 7.48 11 16 7.44 7.52 7.48


Sr # Time(Min) Pk-Pk(V) Pk-Pk(V) Avg Pk-Pk 1 0 1.44 1.5 1.47 2 2 1.68 1.76 1.72 3 4 1.44 1.52 1.48 4 6 1.2 1.28 1.24 5 8 1.36 1.44 1.4 6 10 1.68 1.76 1.72 7 12 1.2 1.28 1.24 8 13 1.32 1.44 1.38 9 14 1.92 2 1.96 10 15 6.24 6.32 6.28 11 16 6.24 6.24 6.24


Sr # Time(Min) Pk-Pk(V) Pk-Pk(V) Avg Pk-Pk 1 0 1.44 1.52 1.48 2 2 1.68 1.76 1.72 3 4 1.36 1.44 1.4 4 6 1.2 1.38 1.29 5 8 1.52 1.6 1.56 6 10 1.2 1.28 1.24 7 12 1.2 1.28 1.24 8 13 2 2.08 2.04 9 14 5.28 5.36 5.32 10 15 5.28 5.36 5.32 11 16 5.36 5.44 5.4

68

Table 4.9 Heating Time in De-ionized water and respective voltage at 50Hz

Sr # Time(Min) Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk 1 0 8.56 8.64 8.6 2 5 5.76 5.84 5.8 3 10 5.12 5.2 5.16 4 15 5.04 5.2 5.12 5 20 4.72 5.04 4.88 6 25 5.04 5.52 5.28 7 30 4.88 5.36 5.12 8 35 4.96 5.36 5.16 9 40 4.96 5.28 5.12 10 45 5.36 5.68 5.52 11 50 5.12 5.64 5.38





69



Table 4.13 Drying time after taking out from de-ionized water at various

frequencies

50Hz 100Hz 150Hz 200Hz Sr # Time

(Min) Avg Pk-Pk Avg Pk-Pk Avg Pk-Pk Avg Pk-Pk 1 0 5.38 5.48 4.75 4.4 2 1 5.32 5.48 5.24 4.68 3 2 5.32 5.48 5.16 4.6 4 3 5.4 6.2 5.42 4.6 5 4 5.4 6.2 4.84 4.84 6 5 5.4 6.2 5.08 5 7 6 5.8 6.4 5.56 5.08 8 7 5.8 6.4 5.88 5.08 9 8 5.8 6.4 5.88 5.08 10 9 6.8 6.4 5.88 5.08 11 10 6.8 6.8 5.96 5.12 12 11 7.2 6.8 5.96 5.12 13 12 7.2 6.8 5.96 5.16 14 13 7.6 6.8 5.96 5.08 15 14 7.96 7.2 5.96 5.08 16 15 7.88 7.2 5.88 5.08 17 16 7.8 7.2 5.88 5.08 18 17 7.76 6.6 5.88 5.08 19 18 7.88 6.6 5.88 5.08 20 19 8.2 6.6 5.8 5.08 21 20 8.2 6.6 5.8 5.08 22 21 8.24 6.8 5.8 5.08 23 22 8.4 6.8 5.64 5.08 24 23 8.48 7 5.96 5.04 25 24 8.52 7 6.2 5

70

26 25 8.52 7.2 6.2 4.96 27 26 8.52 7.2 6.2 4.88 28 27 8.56 7.4 6.2 4.88 29 28 8.6 7.4 6.36 4.84 30 29 8.6 7.48 6.36 5.24 31 30 8.6 7.48 6.36 5.24 32 31 5.24 33 32 5.32 34 33 5.32 35 34 5.32 36 35 5.32

Table 4.14 Heating Time in NaCl solution and respective voltage at 50&100Hz

50Hz 100Hz Time(Min) Pk-Pk (V) Pk-Pk(V) Avg Pk-Pk Pk-Pk (V) Pk-Pk(V) Avg Pk-Pk

0 8.56 8.64 8.6 7.44 7.52 7.48 5 0.32 0.4 0.36 0.32 0.4 0.36 10 0.32 0.4 0.36 0.32 0.4 0.36 15 0.32 0.4 0.36 0.32 0.4 0.36 20 0.32 0.4 0.36 0.32 0.4 0.36 25 0.32 0.4 0.36 0.32 0.4 0.36 30 0.32 0.4 0.36 0.32 0.4 0.36 35 0.32 0.4 0.36 0.32 0.4 0.36 40 0.32 0.4 0.36 0.32 0.4 0.36 45 0.32 0.4 0.36 0.32 0.4 0.36

Table 4.15 Heating Time in NaCl solution and respective voltage at 150&200Hz

150Hz 200Hz Time(Min) Pk-Pk (V) Pk-Pk(V) Avg Pk-Pk Pk-Pk (V) Pk-Pk(V) Avg Pk-Pk

0 6.4 6.48 6.44 5.44 5.52 5.48 5 0.32 0.4 0.36 0.32 0.4 0.36 10 0.32 0.4 0.36 0.32 0.4 0.36 15 0.32 0.4 0.36 0.32 0.4 0.36 20 0.32 0.4 0.36 0.32 0.4 0.36 25 0.32 0.4 0.36 0.32 0.4 0.36 30 0.32 0.4 0.36 0.32 0.4 0.36 35 0.32 0.4 0.36 0.32 0.4 0.36 40 0.32 0.4 0.36 0.32 0.4 0.36 45 0.32 0.4 0.36 0.32 0.4 0.36

71

Table 4.16 Drying Time after taking out from NaCl solution at 50 & 100Hz

50Hz 100Hz Time(Min) Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk

0 0.32 0.4 0.36 0.32 0.4 0.36 1 0.32 0.4 0.36 0.32 0.4 0.36 2 0.4 0.48 0.44 0.32 0.4 0.36 3 0.4 0.48 0.44 0.32 0.4 0.36 4 0.4 0.48 0.44 0.32 0.4 0.36 5 0.4 0.48 0.44 0.32 0.4 0.36 6 0.48 0.48 0.48 0.4 0.48 0.44 7 0.48 0.56 0.52 0.4 0.48 0.44 8 0.48 0.56 0.52 0.4 0.48 0.44 9 0.48 0.56 0.52 0.4 0.48 0.44 10 0.48 0.56 0.52 0.4 0.48 0.44 11 0.48 0.56 0.52 0.4 0.48 0.44 12 0.4 0.48 0.44 0.4 0.48 0.44 13 0.4 0.48 0.44 0.4 0.48 0.44 14 0.4 0.48 0.44 0.4 0.48 0.44 15 0.4 0.48 0.44 0.4 0.48 0.44 16 0.4 0.48 0.44 0.4 0.48 0.44 17 0.4 0.48 0.44 0.4 0.48 0.44 18 0.4 0.48 0.44 0.4 0.48 0.44 19 0.56 0.64 0.6 0.4 0.48 0.44 20 0.56 0.64 0.6 0.4 0.48 0.44 21 0.64 0.72 0.68 0.48 0.56 0.52 22 0.64 0.72 0.68 0.48 0.56 0.52 23 0.72 0.8 0.76 0.48 0.56 0.52 24 1.52 1.6 1.56 0.48 0.56 0.52 25 1.6 1.68 1.64 0.56 0.64 0.6 26 1.68 1.76 1.72 0.8 0.88 0.84 27 1.76 1.84 1.8 0.88 0.96 0.92 28 1.84 1.92 1.88 0.88 0.96 0.92 29 2 2.08 2.04 1.36 1.44 1.4 30 2.08 2.16 2.12 1.44 1.52 1.48 31 2.32 2.4 2.36 1.44 1.52 1.48 32 2.48 2.56 2.52 1.44 1.52 1.48 33 2.96 3.04 3 1.44 1.52 1.48 34 3.28 3.36 3.32 1.52 1.6 1.56 35 3.6 3.68 3.64 1.52 1.6 1.56 36 4.08 4.16 4.12 1.52 1.6 1.56 37 4.4 4.48 4.44 1.52 1.6 1.56 38 4.72 4.88 4.8 1.6 1.68 1.64 39 5.12 5.2 5.16 1.6 1.68 1.64 40 5.44 5.52 5.48 1.6 1.68 1.64 41 5.76 5.84 5.8 1.6 1.68 1.64 42 6.08 6.16 6.12 1.6 1.68 1.64

72

43 6.24 6.32 6.28 1.6 1.68 1.64 44 6.8 6.8 6.8 1.6 1.68 1.64 45 7.04 7.12 7.08 1.68 1.76 1.72 46 7.28 7.36 7.32 1.68 1.76 1.72 47 7.52 7.6 7.56 1.68 1.76 1.72 48 7.68 7.76 7.72 1.68 1.76 1.72 49 7.92 8 7.96 1.68 1.76 1.72 50 7.92 8 7.96 1.76 1.84 1.8 51 8 8.08 8.04 1.76 1.84 1.8 52 8 8.08 8.04 1.76 1.84 1.8 53 8.16 8.24 8.2 1.76 1.84 1.8 54 8.24 8.32 8.28 1.76 1.84 1.8 55 8.24 8.32 8.28 1.76 1.84 1.8 56 8.32 8.4 8.36 1.84 1.92 1.88 57 8.4 8.48 8.44 1.84 1.92 1.88 58 8.4 8.48 8.44 1.92 2 1.96 59 8.48 8.56 8.52 2 2.08 2.04 60 8.56 8.64 8.6 2.16 2.24 2.2 61 2.24 2.32 2.28 62 2.24 2.32 2.28 63 2.4 2.48 2.44 64 2.48 2.56 2.52 65 2.64 2.72 2.68 66 2.72 2.8 2.76 67 2.88 2.96 2.92 68 2.96 3.04 3 69 3.12 3.2 3.16 70 3.2 3.28 3.24 71 3.36 3.44 3.4 72 3.44 3.52 3.48 73 3.52 3.6 3.56 74 3.68 3.76 3.72 75 3.84 3.92 3.88 76 4 4.08 4.04 77 4.16 4.24 4.2 78 4.24 4.32 4.28 79 4.4 4.48 4.44 80 4.48 4.56 4.52 81 4.64 4.72 4.68 82 4.8 4.88 4.84 83 4.88 4.96 4.92 84 4.96 5.04 5 85 5.12 5.2 5.16 86 5.2 5.28 5.24 87 5.28 5.36 5.32 88 5.36 5.44 5.4 89 5.44 5.52 5.48 90 5.52 5.6 5.56 91 5.6 5.68 5.64

73

92 5.68 5.76 5.72 93 5.76 5.84 5.8 94 5.84 5.92 5.88 95 5.92 6 5.96 96 6 6.08 6.04 97 6.08 6.16 6.12 98 6.16 6.24 6.2 99 6.16 6.24 6.2 100 6.24 6.32 6.28 101 6.24 6.32 6.28 102 6.32 6.4 6.36 103 6.4 6.48 6.44 104 6.48 6.56 6.52 105 6.48 6.56 6.52 106 6.48 6.56 6.52 107 6.56 6.64 6.6 108 6.72 6.8 6.76 109 6.88 6.96 6.92 110 6.96 7.04 7 111 7.04 7.12 7.08 112 7.04 7.12 7.08 113 7.2 7.28 7.24 114 7.28 7.36 7.32 115 7.28 7.36 7.32 116 7.36 7.44 7.4 117 7.36 7.44 7.4 118 7.36 7.44 7.4 119 7.44 7.52 7.48 120 7.44 7.52 7.48

Table 4.17 Drying Time after taking out from NaCl solution at 150Hz & 200Hz

150Hz 200Hz Time Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk Pk-Pk (V) Pk-Pk (V) Avg Pk-Pk

0 0.32 0.4 0.36 0.32 0.4 0.36 1 0.32 0.4 0.36 0.32 0.4 0.36 2 0.32 0.4 0.36 0.32 0.4 0.36 3 0.32 0.4 0.36 0.32 0.4 0.36 4 0.32 0.4 0.36 0.32 0.4 0.36 5 0.32 0.4 0.36 0.32 0.4 0.36 6 0.32 0.4 0.36 0.32 0.4 0.36 7 0.32 0.4 0.36 0.32 0.4 0.36 8 0.32 0.4 0.36 0.32 0.4 0.36 9 0.32 0.4 0.36 0.32 0.4 0.36 10 0.32 0.4 0.36 0.32 0.4 0.36 11 0.4 0.48 0.44 0.4 0.48 0.44

74

12 0.4 0.48 0.44 0.4 0.48 0.44 13 0.4 0.48 0.44 0.4 0.48 0.44 14 0.4 0.48 0.44 0.4 0.48 0.44 15 0.4 0.48 0.44 0.56 0.64 0.6 16 0.4 0.48 0.44 0.64 0.72 0.68 17 0.4 0.48 0.44 0.72 0.8 0.76 18 0.4 0.48 0.44 1.2 1.28 1.24 19 0.4 0.48 0.44 2.16 2.24 2.2 20 0.4 0.48 0.44 2.24 2.32 2.28 21 0.48 0.56 0.52 2.4 2.48 2.44 22 0.48 0.56 0.52 2.56 2.64 2.6 23 0.72 0.8 0.76 2.72 2.8 2.76 24 0.8 0.96 0.88 2.88 2.96 2.92 25 0.88 0.96 0.92 2.96 3.04 3 26 0.88 0.96 0.92 3.12 3.2 3.16 27 0.88 0.96 0.92 3.28 3.36 3.32 28 0.88 0.96 0.92 3.44 3.52 3.48 29 0.88 0.96 0.92 3.6 3.68 3.64 30 0.88 0.96 0.92 3.76 3.84 3.8 31 0.96 1.04 1 3.92 4 3.96 32 1.16 1.16 1.16 4.08 4.16 4.12 33 2 2 2 4.16 4.24 4.2 34 2.08 2.16 2.12 4.32 4.4 4.36 35 2.16 2.24 2.2 4.48 4.56 4.52 36 2.24 2.32 2.28 4.56 4.64 4.6 37 2.24 2.32 2.28 4.64 4.72 4.68 38 2.32 2.4 2.36 4.8 4.88 4.84 39 2.48 2.56 2.52 4.88 4.96 4.92 40 2.56 2.64 2.6 4.96 5.04 5 41 2.56 2.64 2.6 5.04 5.12 5.08 42 2.64 2.72 2.68 5.12 5.2 5.16 43 2.72 2.8 2.76 5.12 5.2 5.16 44 2.88 2.96 2.92 5.12 5.2 5.16 45 3.04 3.12 3.08 5.2 5.28 5.24 46 3.12 3.2 3.16 5.2 5.28 5.24 47 3.2 3.28 3.24 5.2 5.28 5.24 48 3.36 3.44 3.4 5.28 5.36 5.32 49 3.44 3.52 3.48 5.28 5.36 5.32 50 3.52 3.6 3.56 5.28 5.36 5.32 51 3.68 3.76 3.72 5.28 5.36 5.32 52 3.76 3.84 3.8 5.28 5.36 5.32 53 3.84 3.92 3.88 5.36 5.44 5.4 54 3.92 4 3.96 5.36 5.44 5.4 55 4.08 4.16 4.12 5.36 5.44 5.4 56 4.16 4.24 4.2 5.36 5.44 5.4 57 4.32 4.4 4.36 5.36 5.44 5.4 58 4.48 4.56 4.52 5.36 5.44 5.4 59 4.64 4.72 4.68 5.44 5.52 5.48

75

60 4.8 4.88 4.84 5.44 5.52 5.48 61 4.88 4.96 4.92 62 4.96 5.04 5 63 5.12 5.2 5.16 64 5.2 5.28 5.24 65 5.28 5.36 5.32 66 5.36 5.44 5.4 67 5.52 5.6 5.56 68 5.6 5.68 5.64 69 5.68 5.76 5.72 70 5.76 5.84 5.8 71 5.84 5.92 5.88 72 5.92 6 5.96 73 5.92 6 5.96 74 6 6.08 6.04 75 6.08 6.16 6.12 76 6.08 6.16 6.12 77 6.08 6.16 6.12 78 6.08 6.16 6.12 79 6.08 6.16 6.12 80 6.08 6.16 6.12 81 6.08 6.16 6.12 82 6.16 6.24 6.2 83 6.16 6.24 6.2 84 6.16 6.24 6.2 85 6.16 6.24 6.2 86 6.16 6.24 6.2 87 6.16 6.24 6.2 88 6.24 6.32 6.28 89 6.24 6.32 6.28 90 6.24 6.32 6.28 91 6.24 6.32 6.28 92 6.24 6.32 6.28 93 6.32 6.4 6.36 94 6.32 6.4 6.36 95 6.32 6.4 6.36 96 6.32 6.4 6.36 97 6.32 6.4 6.36 98 6.32 6.4 6.36 99 6.4 6.48 6.44

100 6.4 6.48 6.44

76

0123456789

0 10 20 30 40 50

Heating Time(Min)

Pk-P

k V

olta

ge(V

)50 Hz

100 HZ

150 Hz

200 Hz

Fig-4.3. Heating time as a function of peak to peak voltage in ordinary water.

0123456789

0 5 10 15 20

Drying Time (Min)

Pk-P

k V

olta

ge (V

)

50 Hz

100 Hz

150 Hz

200 Hz

Fig-4.4 The change in voltage as a function of drying time after immersion in ordinary water.

77

0

2

4

6

8

10

0 20 40 60Heating Time (Min)

Pk-P

k V

olta

ge(V

)

50 Hz

100 Hz

150 Hz

200 Hz

Fig-4.5 Heating time as a function of peak to peak voltage in de-ionized water.

0

2

4

6

8

10

0 10 20 30 40Drying Time (Min)

Pk-P

k Vo

ltage

(V)

50 Hz

100 Hz

150 Hz

200 Hz

Fig-4.6 The change in voltage as a function of drying time after immersion in de-ionized water.

78

0123456789

10

0 10 20 30 40 50Heating time (Min)

Pk-P

k Vo

ltage

(V)

50 Hz

100 Hz

150 Hz

200 Hz

Fig-4.7 Heating time as a function of peak to peak voltage in NaCl solution.

0

1

2

3

4

5

6

7

8

9

10

0 20 40 60 80 100 120 140

Cooling Time (Min)

Pk-P

k V

olta

ge (V

)

50 Hz

100 Hz

150 Hz

200 Hz

Fig-4.8 The change in voltage as a function of drying time after immersion in NaCl solution.

All measurements have been taken at just taken out from water (i.e.. in air). However, if

the peak to peak potential was recorded with the PZT ceramic immersed in water a much

lower value was recorded, for instance 400mV was observed for immersion in ordinary

79

water, in de-ionized water this value was 700mV, and 320mV when dipped in NaCl

solution. Interestingly, when the PZT ceramic was left to stand in air, the peak to peak

potential values returned to their original peaks. The time to return its original value was

about 15 minutes for PZT immersed in water (Fig.4.4) and about 30 minutes for PZT

after immersion in de-ionized water (Fig.4.6). However PZT disc in NaCl solution regain

to its original potential value in one to two hours depending upon the change in frequency

(Fig. 4.8). The difference in drying time between water, de-ionized water and NaCl

solution was attributed to the differences in chemistry of the 3 water conditions. The de-

ionized water lacks ions responsible for dissipating charge from the PZT surfaces, and the

mass effect created by the presence of impurities in the water which will adhere to the

surfaces of the ceramic can affect the peak to peak voltage differences observed between

the solutions.

The properties of PZT ceramics are frequency and temperature dependent. The exact

value for time varied depending on the frequencies used during the test is natural

phenomenon of piezoelectric. As the water particles adhere on the surface after

immersion, reduces the flow of current across the disc and therefore peak-peal voltage

sharply decrease. As long as disc dried, the flow of current increase and after few minutes

it regain its original value when completely dry. The difference in drying time of disc for

water and de-ionized water was attributed to the differences in chemistry between the

different water conditions. The de-ionized water lacks ions responsible for dissipating

charge from the PZT surfaces. The mass effect created by the presence of impurities in

the water which adhere to the surfaces of the ceramic can affect the peak to peak voltage

differences observed between the solutions. The lack of ions in de-ionized water may

80

increase the resistance and hence drop in voltage is less as compared to ordinary water.

The most noticeable behavior was seen when the PZT ceramic was immersed in a

solution of NaCl as shown in Fig.4.7 and Fig.4.8. A significant decrease in potential was

observed for the PZT ceramic with values dropping to 320mV after the immersion tests.

When the PZT ceramic was allowed to dry in air the disc took a longer time to regain its

original potential value depending on the frequency used during the test. This is because

of the crystalline nature of NaCl, its particles adhere to the surface and took a longer time

to evaporate and hence to regain its original output value in long time. These results

clearly showed that the PZT ceramic is sensitive to the type of solution in contact with

the ceramic surface. Earlier W.P.Chen [68] observed the degradation phenomenon in

PZT ring for determination of its various piezoelectric properties in NaOH solution by

electrolysis of water and by high power resonant driving. In their study degradation in

capacitance, dielectric loss, impedance and Pk-Pk voltage change with respect to time

and frequency have been examined. In contrast to these above stated properties, the

present work has been conducted to measure the performance characteristics of PZT disc

in water and NaCl solution in heating cycle with respect to time at variable frequencies.

Previous findings [66, 68] clearly state that the change in temperature changes the out put

peak to peak voltage and other piezoelectric properties of PZT. The work conducted by

Jiang [71] concluded that piezoelectric devices seriously degrade by hydrogen in water

due to electricity. Atomic hydrogen formed by electrolysis of water degrades dielectric

and mechanical quality factor with respect to hydrogen charging time. The present work

has an agreement with their finding in changing the Pk-Pk voltage with time at variable

frequencies. Influence of hydrogen charging on the current-voltage characteristics of a

81

PZT ring measured by Jiang [71] resulted in the form of decrease in resistivity of the

sample. This decrease in resistivity is due to the reduction reaction of atomic hydrogen

resulting in the formation of charge carriers in piezoelectric ceramics material. In figures

4.3, 4.5 &4.7, it is clear that the drop in voltage occurs, which is due to decrease in

resistance across the disc and a well documented phenomenon as discussed by earlier

researchers. Another parameter observed in the current research work is the ability of

material to retain the original potentials.

Effect of heating rate on dielectric and pyroelectric properties of PZT have been reported

by Mohiddon [73] and founded that heating rate influence the capacitance and dielectric

properties. Increasing heating rate reduces the level of evaporation. In present work a

qualitative data obtained during the drying cycle of PZT disc after immersion test till the

complete evaporation. Here the test was conducted at constant heating and cooling rate

but a change in peak-peak voltage has also been observed and shown in figures 4.4, 4.6

&4.8. This change in potential is attributed to the change of medium and frequency.

Therefore there is a scope of further research to conduct the same experimentation at

different heating and cooling rate to observe the performance characteristics of thin PZT

in various environmental conditions.

82

4.3 Phase-2 Thermal cycling/shocking of thin PZT disc

Earlier fatigue studies showed that materials degrade due to change in

environmental temperatures. Thermal shocking is one of the most severe phenomenons in

degradation of piezoelectric ceramics. A lead zirconate titanate thin piezoelectric disc has

been analyzed to observe its thermal cycling/shocking effect.

4.3.1 Specimen

A Lead Zirconate Titanate piezoelectric disc 0.191mm thick and 12.7mm

diameter supplied by Piezo System Inc. used for the experimentation. The specimen was

nickel electroded on major faces and its dielectric constant was about 1850 @1KHz,

Curie temperature 3500C, and density 7800 Kg/m3. In this case the specimen was not

soldered and was used as in its as received form.

4.3.2 Instrumentation

The instrumentation used in this case has also been described in chapter-3. Thin

PZT disc was placed on a small metallic strip and a spring loaded thermocouple was

directly attached on upper surface of the disc. Thermocouple attached with data

acquisition system which indicate the temperature of the specimen. A stop watch used to

measure the time to reach at specific temperature.

4.3.3 Testing/Measurements

Following experimentations were done at different condition to analyze the

degradation in piezoelectric properties. All testing were done well below the curie

temperature of the piezoelectric specimen.

83

1. Thermal shocking from 1000C from thermal chamber to de-ionized water at 200C.

2. Thermal cycling test between 1000C and 900C for 60 cycles in step of 10 cycles.

3 Shocked once for 60Cycles between 1000C and 900C

4 Thermal shocking from 1500C & 1000C from thermal chamber to de-ionized

water at 200C.

4.4 Thermal shocking from 1000C from thermal chamber to de-ionized

water at 200C.

A lead zirconate titanate thin piezoelectric disc has been analyzed to observe its thermal

shocking effect. Disc was shocked from 1000C from a thermal chamber environment to

de-ionized water at 200C. Dielectric constant, impedance and coupling factors at

frequency of maximum and minimum impedance have been measured for thirty five

shocks. The change in dielectric constant, Impedance and other piezoelectric parameters

were observed by using relevant instrumentations. The change in degradation will be

very useful in modeling and development of sensitive piezoelectric instruments.

Lead Zirconate Titanate (PZT), Barium Titanate (BaT1O3), and Lead Metaniobate

(PbNb2O6) are smart sensing materials. These materials are being used in critical

engineering systems and smart structures. Piezoelectric materials when undergoes a

cyclic stress during thermal environment may degrade the piezoelectric properties [76].

Heat transfer effect in ferro-electric materials, electric impact loading, thermal effects of

piezoelectric sensors and heat generation rate in piezoelectric materials have also been

investigated by various researchers [77]. Thermal shocks in a plate of finite thickness

have been attempted. Thermal shock and thermal fatigue of ferroelectric thin film were

84

investigated by the pulsed laser tests by X.J.Zheng et. al [67]. Fatigue studies show that

material degradation of PZT ceramics are strongly influenced by temperature and by the

electromechanical fatigue. Lead zirconate titanate ceramics shows a decrease in dielectric

constant and the resonance frequency when subjected to thermal shock. Importance of

temperature stability for dielectric constants and resonance frequencies have been

discussed [78]. Thermal shock resistance of the materials was evaluated by water

quenching and a subsequent three point bending test to determine flexure strength

degradation. Degradation of various properties of the piezo devices in the presence of

water & AC voltage was investigated and concluded that water is an important cause for

the degradation of PZT piezoelectric ceramics [72].

Dielectric constant is an important parameter, especially in the piezoelectric device such

as resonators and filters used in the electronic circuits. Impedance is also dependent on the

dielectric constant of the piezoelectric. Currently there is limited data available for the

thermal shocking and quenching effect of a thin PZT disc. In this part of research work,

the focus was to investigate the degradation of thin PZT disc due to thermal shocking and

its quenching effect in de-ionized water. A noticeable change in capacitance and

dielectric constant has been observed which is further changing other piezoelectric

properties. Current research part is a unique finding in thermal shocking and quenching

of thin PZT disc.

85

4.4.1 Test Setup and Variables.

There is no single technique for measuring piezoelectric material characteristics.

However some standards allow measuring some parameters and then using the

appropriate relationships, other piezoelectric parameters can be found.

A piezoelectric thin PZT disc has been investigated under thermal shocking in de ionized

water. Initially the capacitance, dissipation factor, impedance, and phase angle of the as

received specimen have been measured. For the reliability of results two discs have been

used at same time for the shocking and measurements in the same environmental

condition. Rate of change in temperature in thin PZT disc in thermal chamber from 200C

to 1000C and after removing from thermal chamber shocked in de ionized water at 200C

has been clearly shown in Fig.4.9. Disc heated in thermal chamber at rate of

10.860C/min.

0

20

40

60

80

100

120

0 2 4 6 8 10

Time in Minutes

Tem

pera

ture

in C

Fig.4.9 Rate of change in temperature from 200C to 1000C from thermal chamber and shocking at 200C in de-ionized water

86

The specimen was placed in an environmental chamber and heated to 1000C and then

suddenly removed and quenched in de-ionized water at about 200C for a specific time and

then dried. The specimen was again placed in the thermal chamber for the same

temperature range and quenched again. Five such shocks were introduced. The values of

capacitance and impedance after these five shocks were measured at a frequency of

1KHz. and at fm & fn. Six series each with five shocks have been performed and their

respective capacitance and impedance values have been measured. Data collected for

thirty five such shocks and analyzed for the degradation in dielectric constant and

coupling factor. Frequencies of maximum and minimum impedance were observed

between 100 KHz and 200KHz. Capacitance and Impedance at theses particular

frequencies were recorded. The values of capacitance were used to calculate the dielectric

constant by using equation-4.1.

Effective and Transverse coupling factors has been determined by using the relationships

4.2 and 4.3

Where Ψ = π/2(fn/fm) * tan |π/2 * (fn-fm)/fm|

30

ta x CpK T

A x =

∈

Keff =

K31 = SQRT (ψ/(1+ψ)

(4.1)

SQRT (fn2 – fm

2)/fn2

(4.2)

(4.3)

87

Capacitance and impedance of the tested specimen were measured by using impedance

analyzer and dielectric text fixture. Dielectric test fixture model 16451B was selected as

fixture for the testing material. The fixture was attached with LCR meter and impedance

analyzer 4294A which use the 4-terminal pair measurement configuration. Electrode-D

of the test fixture was selected for measurements. This electrode is appropriate to

measure those materials which already have thin film electrodes. The values obtained

from impedance analyzer then used for the calculation of dielectric constant, and

coupling factors (Keff, and K31). Table-4.18 indicates the values obtained and used for

the calculation of above mentioned parameters according to the IEEE standard [53].

Table-4.18 Values of Capacitance Coupling factors and dielectric constant w.r.t.

frequency of maximum (fm) and frequency of minimum (fn) impedance.

fm fn Cpat1KHz Cp atfm Cp at fn Keff K31 K3

T at fm Shock# Hz Hz pF pF pF

0 160000 165500 10880 58040 -52967 0.255 0.279 9888 5 156785 165106 11100 55650 -53045 0.313 0.34 9481 10 151570 160270 11220 45350 -36430 0.324 0.352 7726 15 147075 154530 11330 37520 -22150 0.306 0.333 6392 20 142000 152500 11260 31060 -16741 0.364 0.393 5291 25 141000 156000 11280 28120 -11570 0.427 0.457 4790 30 123000 157000 11320 20250 -1140 0.621 0.644 3450 35 116500 153500 11320 17230 250.35 0.651 0.671 2935

Impedance analyzer and test fixture is shown in figure 4.10.

88

Fig. 4.10 Impedance analyzer connected with test fixture for measuring various parameters (Impedance, Capacitance, Dissipation factor, Phase angle).

4.4.2 RESULTS ANALYSIS

The measurement of capacitance and dielectric constant during thermal shocking was

done by precise instrumentation. The latest impedance analyzers and compatible test

fixtures have the capability to measure these parameters accurately. The dielectric

constant and coupling factor were measured as a function of frequency of maximum

impedance and frequency of minimum impedance. Thin disc shocked in de-ionized water

shows a noticeable difference between shocked and unshocked condition at frequency of

maximum impedance and at frequency of minimum impedance. This difference has been

thought to be attributed due to change in dipole movement and direction. Affect on grain

size if any is not considered in this study as beyond the scope of preset work. Shocked

Materials capacitance values measured before testing and after every five shocks. Fig-

4.11 (a&b) indicate the capacitance values at frequency of maximum and minimum

89

impedance before conduction of test for which only one peak has been observed , where

as the number of peaks have been observed for the shocked material at frequency of

maximum and minimum impedance and clearly indicated in Fig-4.12(a&b). Dissipation

factor is also greatly affected by thermal shocking conditions as indicated in Fig 4.11&

4.12. With the measurements conducted after every five shocks, values for maximum and

minimum impedance has been observed at different frequencies. The value of

capacitance at frequency of maximum and minimum impedance shows very interesting

results. The detailed experimental results images have been presented in Appendix-A

90

(a)

(b)

Fig-4.11 Value of capacitance for Un-shocked Disc (a). Capacitance at frequency of

maximum impedance. (b). Capacitance at frequency of minimum impedance.

91

(a)

(b)

Fig-4.12 Value of capacitance after thirty five shocks



92

-10000

-5000

0

5000

10000

15000

0 10 20 30 40

Number of shocks

Die

lect

ric c

onst

ant i

n pF

At 1KHz

fm 100C

fn 100C

Fig-4.13 Change in Dielectric constant w.r.t. Number of shocks

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 10 20 30 40Number of shocks

Cou

plin

g fa

ctor

Keff

K31

Fig-4.14 Coupling Factors with respect to Number of Shocks

93

Frequency of maximum impedance observed for unshocked specimen was 160 KHz,

where as after thirty five shocks it was about 116.5 KHz which is approximately 28

percent less from the unshocked value. Similarly frequency of minimum impedance

observed at 165.5 KHz for unshocked and 153.5 KHz for socked specimen which is only

7.5 percent less from unshocked specimen value. This difference shows that the

maximum and minimum resonance is dependent on their respective frequencies. It is

observed that value of capacitance continuously going to decrease from initial to shock

condition at frequency of maximum impedance and reverse at frequency of minimum

impedance. By using equation-4.1 dielectric constant calculated with respect to number

of shocks and indicated in Fig.4.13. Dielectric constant is very important property and

depends upon the physical condition of the material. The change in dielectric constant in

this work clearly indicates that physical condition of the material has been changed due to

change in dipole lengths and directions. The change in capacitance and the relative

dielectric constant is due to dipole moments inside the material. Due to thermal shocks,

the displacement of electrons may cause re-orientation of these dipoles. The

misalignment of polarization and displacement of charge may result in random

orientation of the dipoles, which further changes its capacitance and dielectric values.

The description of dielectric constant is very difficult in thermal cycling problems

because the orientations of molecular size dipoles changes frequently in such shocking

conditions. Theory becomes more difficult because of electrostatic interaction between

dipoles. However, the measurement of fm and fn is one of the reliable methods to

determine the capacitance value at particular frequency. The relative difference in the

frequencies of maximum and minimum impedance depends on both the material coupling

94

factor and resonator geometry. For this reason a quantity called the effective coupling

factor has been used. Effective and transverse excitation coupling factor has been plotted

by using equation-4.2 & 4.3 and indicated in Fig.4.14. Earlier the stress dependence of

electromechanical properties of various piezoelectric ceramics has been reported.

Viehland [79] found that coupling coefficients and piezoelectric coefficients are

relatively high under stress. He determined the effect of uniaxial stress upon the

electromechanical properties of various piezoelectric ceramics. The change in values was

observed with the change in stress and electric field. In the present work, effective and

transverse excitation coupling factors have been determined by resonance method. After

thermal shocking, the transverse and effective coupling factors increased and became

very close to each other. The decrease in fm was accompanied by decrease in fn and their

difference was continuously increasing with thermal shocking. This difference resulted in

the increase in coupling factor. A thermal stress developed in the thin PZT due the

thermal shock that may have caused an increase in the coupling factor. It was observed

during the experimentation that wrong selection of guarded electrode and the distance of

PZT disc from the edges under the guarded electrode may affect the results. Therefore,

for the reliability of the results, the values were taken with absolute care in placing the

specimen under the electrode, and were repeated for shocking and measurements.

Trend for both coupling factors is in increasing order and show very close agreement to

each other.

95

4.5 Phase-2 (Series 2) Thermal shocking from 1500C & 1000C from

thermal chamber to de- ionized water at 200C.

Earlier thermal shocks in a plate of finite thickness have been attempted. Fatigue studies

show that material degradation of PZT ceramics are strongly influenced by temperature.

Lead zirconate titanate ceramics shows a decrease in dielectric constant and the resonance

frequency when subjected to thermal shock. In many piezoelectric applications, materials

with high dielectric constant and high electromechanical factor are required. It has been

reported that dielectric constant increases with heating rate increase [80].Other studies

reported that increasing heating rate may affect the evaporation and optimum dielectric

constant found at certain specific value [81]. Thermal fatigue test method include the

quench method and repeated heating method has been for thermal shocks and discussed

earlier by Lamon and Pherson (1981, 1991) [82, 83].Therefore there was a scope to

investigate these important behaviors of the materials during different thermal shocking

temperatures. Water is an important cause of degradation of a PZT ceramics. The

experimental results obtained have been compared between both shocking conditions and

the sensitivity between two shocking ranges has been observed.

4.5.1 EXPERIMENTATION

Sudden heating and cooling of piezoelectric ceramics material may cause high

value of stresses and therefore change in internal properties of the material may occur. In

this series thin lead zirconate titanate discs have been investigated during thermal

shocking in de-ionized water from 1000C to 200C and from 1500C to 200C.

96

Experimentation was performed for thirty five shocks and their relative dielectric

constant, coupling factor and impedance have been measured. A Lead Zirconate Titanate

piezoelectric disc nickel electroded on major faces, 0.19mm thick and 12.7mm in

diameter was used for the experimentation. Thin piezoelectric ceramic discs were heated

using a heating rate of 9oC/min up to 100oC, and 1500C using a thermal chamber and then

quenched in de-ionized water at a temperature 20oC. For all thermal cycling and

quenching experiments 2 PZT test samples were used and subjected to identical

conditions in order to confirm reliability. The temperature of the PZT samples were

measured using a spring loaded thermocouple and data acquisition system attached

directly to the samples. In order to observe degradation phenomenon of the PZT ceramic,

the capacitance, dissipation factor and impedance were measured at a frequency of 1 KHz

at the start and after every 5 heating and quenching cycles. Data was collected for a total

of 35 thermal cycles. All described parameters were also measured at frequencies of

maximum and minimum impedance by using impedance analyzer. By considering

various frequency ranges, the frequency of maximum and minimum impedance was

observed between 100 KHz and 200 KHz Change in dielectric constant, coupling factor

and impedance for thirty five shocks in de-ionized water has been tabulated in Table-

4.19. The recorded values are at 1 KHz and at a frequency of maximum impedance.

97

Table-4.19 Change in Dielectric Constant and Coupling Factor for two Different Thermal Shocking Conditions. Shocking from 1000C to 200C Shocking from 1500C to 200C

Shock# TK 3

at 1KHz

TK 3 at fm effK 31K

TK 3 at 1KHz

TK 3 at fm effK 31K

0 1853 9888 0.255 0.279 1869 10462 0.23 0.26 5 1891 9481 0.313 0.34 1915 8532 0.27 0.29

10 1911 7726 0.324 0.352 1923 7005 0.3 0.32 15 1930 6392 0.306 0.333 1932 4366 0.32 0.35 20 1918 5291 0.364 0.393 1954 3926 0.34 0.37 25 1922 4790 0.427 0.457 1976 3504 0.36 0.38 30 1928 3450 0.621 0.644 1976 3912 0.41 0.41 35 1928 2935 0.651 0.671 1976 4121 0.44 0.47

4.5.2 RESULT ANALYSIS

The changes in dielectric constant and coupling factor were measured as a

function of fm and fn. It is observed that an increase in the value for the capacitance of the

as-received PZT ceramic was 5.8 x 104 pF and this value gradually decreased with

increasing thermal cycling (1000C-200C)to 1.72 x 104 pF. A corresponding change in the

fm was observed with a value of 160 KHz for the PZT sample at the start and then the

value decreased to 116.5 KHz. This represented a 28% decrease in the fm after the

ceramic was thermally cycled. A similar change was observed for the fn which decreased

from 165.5 KHz for the as-received to 153.3 KHz after 35 thermal cycles. For the thermal

cycling (1500C-200C) change in fm observed from 160.2 KHz to 141 KHz and this change

is from 165.175 KHz to 157.5 KHz at fn.

A comparison of the graphical output for dielectric constant for the PZT samples before

thermal cycling and then after exposing the ceramic to 35 heating and quenching cycles is

shown in Fig.4.15. Dielectric constant remains independent when measured at 1 KHz.

The dielectric constant is an intrinsic property of the ceramic material and the results

98

show that this value decreases with increasing thermal cycles at fm and vice versa. The

relative difference in the frequencies of the maximum and minimum impedance values

depends on the material coupling factor and the resonator geometry (i.e.. dimensions of

the ceramic PZT sample). For this reason a quantity known as the effective coupling

factor (Keff) and the transverse excitation factor (K31) calculated and were compared as a

function of the number of thermal cycles, see Fig.4.16. The results show that both

temperature difference values for K31 and Keff increase with increasing thermal cycles to

which the PZT ceramic is exposed.

Figure 4.15. Chang in dielectric constant against number of shocks, at frequency

1 KHz, at frequency of maximum impedance, at frequency of minimum impedance.

-15000

-10000

-5000

0

5000

10000

15000

0 10 20 30 40

Die

lectr

ic c

on

sta

nt in

pF

Number of shocks

Shocking from 100 0C – 20 0C at 1KHZ.

100 0C – 20 0 C at fm.

100 0C – 20 0 C at fn. 150 0C – 20 0 C at 1KHz.

150 0C – 20 0 C at fm.

150 0C – 20 0 C at fn.

99

Shocked from

100 0C - 20 0C at fm.

100 0C - 20 0C at fn.

150 0C - 20 0C at fm.

150 0C - 20 0C at fn.

Figure 4.16. Change in coupling factor (K31, Keff) against number of shocks from

100 0C – 20 0C & from 150 0C – 20 0C in de-ionized water.

0

20

40

60

80

100

120

140

160

0 10 20 30 40Number of Cycles

Mod

ulus

of I

mpe

danc

e in

O

hms

Figure 4.17. Change in Modulus of impedance ( |Z| ) against number of shocks from

100 0C – 20 0C & from 150 0C – 20 0C in de-ionized water.

The change in Modulus of Impedance for two different shocking conditions has been

evaluated and is shown in fig.4.17. The Modulus of impedance both for fm and fn when

shocked from 1000C to 200C, going to increase where as for the other condition it starts

decreasing after twenty five shocks.

Resonance and anti resonance frequencies are the measure of electromechanical coupling

factor. The coupling between the electrical excitation and mechanical vibration determine

Shocked from

Keff, 100 0C - 20 0C

K31, 100 0C - 20 0C

Keff, 150 0C - 20 0C

K31, 150 0C - 20 0C0

0.2

0.4

0.6

0.8

0 10 20 30 40Number of shocks

Cou

plin

g fa

ctor

100

its piezoelectric effect. Mechanical vibrations appears like a series LCR circuit to the ac

source. Such circuits have minimum impedance at certain frequency called resonance

frequency (fn). There is another frequency at the other end and is called anti-resonance

frequency (fm). The change in electromechanical coupling factor changes the out put

performance and characteristics of the piezoelectric material by thermal shocking.

The comprehensive results with images have been presented in Appendix-A.

101

4.6 .Phase-3 (Series 3) Effect of Frequency and Resistance on Pk-Pk

Voltage with respect to Temperature Change

This phase describes the experimentations performed on thin PZT disc for the

determination of its thermal cycling behavior at a specific temperature ranges and at

different frequencies and resistances. The aim was to determine the output voltage across

the specimen at different variables. A mathematical model has been developed for the

specific temperature range at various frequencies to determine the peak-peak voltage and

to demonstrate the effect of frequency with respect to change in resistance. Sensitivity

due to temperature, resistance and frequency was observed. The data recorded and

analyzed will be very useful in selecting the particular range for the output performance

needed for the fabrication of any specific piezoelectric instrumentation. The aim of this

part of work was to analyze the sensitivity of the thin PZT disc in thermal environment.

Lead zirconate titanate (PZT) ceramics materials are widely used in various applications

like in micro sensors, actuators, resonators, vibrators, etc. The functioning of these smart

materials is very much depended on various conditions such as change in frequency,

resistance and temperature etc. These variables may affect the output performance of the

instrument in which they used and therefore considered highly sensitive.

Reliability of instruments is very important and research has been carried out on PZT and

BatiO3 (Barium titanate) thin films. Piezoelectric coefficients are temperature dependent

in PZT film and this temperature change may expect in variation of output signals. A

frequency response measurement has been used to measure the sensitivity of

piezoelectric devices [84]. Piezoelectric have been investigated for their thermoelectric

102

behaviors and various governing equations for thermal affects has been described [85].

P.K. Panda et. al. in their investigation analyzed that thermal stresses is sensitive to

thickness of samples and, therefore, they recommended using various samples of same

thickness to get the reliable results [86]. Thermal fatigue methods including quenching

[87] and repeative heating method have been described earlier [88].

Piezoelectric ceramics under electric fields becomes non linear due to domain effects.

Effect of power on the rise of temperature of piezoelectric materials is also an observed

phenomenon. In this research work effect of temperature on thin PZT discs have been

investigated with respect to change in frequency and resistance for the functional

performance in the form of peak to peak voltage. The aim was to determine how these

parameters influence the characteristics of PZT disc at room temperature (200C) and at a

temperature 1600C well below the curie temperature of PZT specimen.

4.6.1 Experimental Setup

Figure-4.18 shows the arrangement for the experimental setup including thermal

chamber, temperature recording system, decade resistor, function generator, oscilloscope

and thermocouple. A schematic diagram of the experimental arrangement showing the

circuitry connections has been described in Fig-4.19

103

Fig-4.18 Experimental arrangement for the determination of out put Peak-Peak voltage

104

Figure 4.19 Schematic Arrangement of Thermal Cycling Circuitry

105

4.6.2 Experimentation

A soldered specimen attached with the described circuitry as shown in Fig-4.19

was mounted in the thermal chamber environment. The measurements were taken at

various temperatures ranges. A WaveTek Model FG-273 function signal generator of

kenwood was used for the excitation of piezo disc at various frequencies. Frequencies

selected were 50, 100, 150, 200, and 300 Hz. Resistances were selected by a decade

resistor type 1434-G of General Radio Company. The range of the decade resistor is 0 to

b1000 KΩ. Out put voltages were obtained by Tektronix TDS 210 oscilloscope. The

voltage across Channel-1 and Channel-2 of the oscilloscope were kept constant at 5V and

2V respectively. The description of the specimen and it properties has been described in

chapter 3. Nickel electroded specimen (Fig.4.20) was soldered and attached with

thermocouple which determines the surrounding temperature of the specimen. Series-1 of

the experiment was performed at room temperature and Series-2 at 160 0C. For the

reliability/validity of results the experimentation was repeated with same specifications

and with same environmental conditions in each Series.

106

Fig-4.20 Piezoelectric PZT disc (diameter 12.7mm and thickness 0.191mm)

4.6.3 Series-1(At Room Temperature)

In this series of experimentation, all measurements were taken at room

temperature. Room temperature was about 200C with a temperature vitiation of ± 20C.

The specimen was attached with the designed circuitry and measurements were taken at

50, 100, 150,200 and 300 Hz. Experimental setup for this series of experimentation is

shown in figure 4.21. The out put Pk-Pk voltage were recorded against resistances. Data

obtained has been recorded and noted in Table-4.20. The value obtained at 0k ohm was

always 10.2 Volt, i.e.. the maximum voltage across the piezo disc without resistance.

This value starts decreasing with the increase in resistance. Figure 4.22 shows the

behavior of voltage drop with respect to increase in resistance. Voltage drops

continuously with the change in resistance, but this decrease is also a frequency

dependent. At the higher values of frequencies the drop in voltage is higher.

107

Fig-4.21 Experimental arrangement for the determination of output voltage at room temperature (200C).

Table-4.20 Change in Pk-Pk Voltage against Resistances at 200C (RT)*

Frequency(Hz) 50Hz 100Hz 150Hz 200Hz 300Hz Resistance(KΩ) Pk-Pk(V) Pk-Pk(V) Pk-Pk(V) Pk-Pk(V) Pk-Pk(V)

0 10.2 10.2 10.2 10.2 10.2 1 10.2 10.2 10.2 10.2 10.2 10 10.1 10.1 10.1 10.1 9.92 20 9.92 10 9.76 9.68 9.28 30 9.84 9.76 9.36 9.2 8.48 40 9.68 9.52 8.96 8.56 7.68 50 9.52 9.28 8.56 8.16 6.96 60 9.44 8.96 8.16 7.6 6.32 70 9.28 8.72 7.76 7.12 5.68 80 9.12 8.4 7.36 6.64 5.28 90 8.96 8.16 6.96 6.24 4.88 100 8.8 7.84 6.56 5.84 4.48 110 8.4 7.36 6.24 5.36 4 200 7.28 5.6 4.16 3.52 2.56 300 6.08 4.24 3.12 2.48 1.84 400 5.12 3.44 2.32 2 1.44 500 4.48 2.88 1.92 1.68 1.2 600 3.92 2.48 1.68 1.44 1.04 700 3.44 2.24 1.52 1.28 0.96 800 3.12 2 1.36 1.2 0.88 900 2.88 1.84 1.2 1.12 0.88

1000 2.72 1.68 1.12 1.04 0.88

108

0

2

4

6

8

10

12

0 200 400 600 800 1000 1200Resistance in K Ohms

Pk-P

k Vo

ltage

(V)

50 HzRT

100HzRT

150HzRT

200 HzRT

300 HzRT

Figure-4.22 Effect of resistance on Pk-Pk voltage at various frequencies at room temperature.

This drop in voltage is high at higher frequency as compared to low frequency. Output

voltage is greatly affected with the resistance. For example, at frequency 50 Hz &

resistance 10 KΩ, the Pk-Pk voltage is 10.1V and at the same resistance, the value at

300Hz is 9.92Volt i.e.. difference in voltage is only 0.18V. The difference is increased to

4.32V at 100 KΩ and further this difference reduces to 1.92V at 1000KΩ. It is also

observed that drop in voltage is very much dependent on frequency. For example at

frequency 50 Hz, the drop in voltage from 10 KΩ to 100KΩ is from 10.1V to 8.8V i.e..

(1.3V), whereas for the same range of resistance and at 300 Hz this value changes from

9.92V to 4.48V i.e.. (5.44). Interestingly this behavior changes from 100KΩ to 1000KΩ.

For this range the drop in voltage at 50Hz is 6.08V and 3.68V at 300Hz. This behavior is

clearly indicated in figure-4.22, that at 50 Hz the drop in voltage from 0-100kΩ is less

and this drop is more from 100-1000KΩ. This phenomenon is reversed at 300Hz which

shows that the maximum drop is from 0-100 KΩ and less decrease for the higher value of

109

resistance. In conclusion it is determined that drop in voltage in piezoelectric disc is very

much dependent on resistance and frequency even at room temperature. The sensitivity

observed will be very useful for the designing of piezoelectric systems for particular

applications.

Table 4.21 indicates the difference in voltage for each hundred resistance band for each

frequency. Fig 4.23 indicates the change in voltage between each 100 K ohms band.

Table 4.21 Difference in voltage for each 100kΩ band at room temperature (200C)

Frequency(Hz) 50Hz 100Hz 150Hz 200Hz 300Hz Resistance(KΩ) Pk-Pk(∆V) Pk-Pk(∆V) Pk-Pk(∆V) Pk-Pk(∆V) Pk-Pk(∆V)

1-100 1.4 2.36 3.64 4.36 5.72 100-200 1.52 2.24 2.4 2.32 1.92 200-300 1.2 1.36 1.04 1.04 0.72 300-400 0.96 0.8 0.8 0.48 0.4 400-500 0.64 0.56 0.4 0.32 0.24 500-600 0.56 0.4 0.24 0.24 0.16 600-700 0.48 0.24 0.16 0.16 0.08 700-800 0.32 0.24 0.16 0.08 0.08 800-900 0.24 0.16 0.16 0.08 0 900-1000 0.16 0.16 0.08 0.08 0

110

0

1

2

3

4

5

6

7

1 2 3 4 5 6 7 8 9 10

Resistance band

Pk-P

k Vo

ltage

(V)

50 Hz100Hz150Hz200Hz300Hz

Figure 4.23 Change in Pk-Pk voltage for each 100kΩ band at 200C

Table-4.22 indicates the resistance ranges i.e.. for each 100 kΩ resistance

band.

Table 4.22 Resistance Range Bands

Band No. Resistance range in kΩ 1 1 - 100 2 100 - 200 3 200 - 300 4 300 - 400 5 400 - 500 6 500 - 600 7 600 - 700 8 700 - 800 9 800 - 900 10 900 - 1000

111

4.6.4 Series -2 (At 1600C)

Piezoelectric disc was analyzed to observe the effect of temperature at variable

resistances. The same disc was mounted in a thermal chamber and its temperature peak

was selected at 1600C. At this temperature Pk-Pk voltage was recorded with respect to

resistance and frequency. All measurements were taken at surrounding environmental

temperature 1600C. The behavior of output voltage was observed by keeping the

reference temperature constant for few minutes. It was observed that there was no effect

of time at this specific temperature. The change in values was observed by changing the

frequencies and resistances are tabulated in table.4.23. Figure-4.24 indicates the behavior

of thin PZT disc for this specific condition. The out put voltage recorded at 50, 100, 150,

200 and 300 Hz frequencies. Overall drop in voltage was more as compared to previous

case at room temperature. For example at this temperature, the Pk-Pk voltage from 10KΩ

-1000KΩ and at 50 Hz changes from 10V to 2V. At room temperature with the same

conditions the drop in voltage was 10.1V to 2.72V. This indicates that temperature is

definitely affecting the output response of PZT disc. At high temperature the drop in

voltage from lower to high value of resistance is high.

There was no change in output voltage at various frequencies at 0 K ohm resistances.

The value of Pk-Pk voltage stared decreasing from 10 K Ω to 1000 K Ω. A threshold

value was 10 K Ω where from the values stars changing. The value for output voltage

obtained at 50 Hz and at 10 K Ω was 10 volts. This value decreases to 2 volts at 1000K

Ω, i.e.. 80% decrease. The decrease in the value was not independent of frequency and

this value continuously decreases with different percentage. At 300 Hz the value at 10 K

Ω was 9.6 volt, and it decreases to 0.64 volt i.e.. 93.33% decrease from 10 k Ω value.

112

This means that voltage drop at low frequency is less as compared to voltage drop at high

frequency. Another interesting behavior was relating to change in Pk-Pk voltage by

changing the resistance value. It is clear in Figure-4.24 that drop in voltage is also

dependent on frequency input and resistances. This drop in voltage is less at low

frequencies, whereas at high value of frequency the output voltage drop is high enough.

Table-4.23 Change in Pk-Pk Voltage with respect to Resistances at 1600C

Frequency(Hz) 50Hz 100Hz 150Hz 200Hz 300Hz Resistance(KΩ) Pk-Pk(V) Pk-Pk(V) Pk-Pk(V) Pk-Pk(V) Pk-Pk(V) 0 10.2 10.2 10.2 10.2 10.2 1 10.2 10.2 10.2 10.2 10.2 10 10 9.92 9.92 9.84 9.6 20 9.84 9.76 9.6 9.2 8.56 30 9.68 9.44 9.04 8.48 7.44 40 9.44 9.12 8.48 7.76 6.48 50 9.36 8.72 8 7.04 5.6 60 9.12 8.32 7.36 6.4 4.96 70 8.88 7.92 6.88 5.84 4.4 80 8.72 7.52 6.4 5.36 4 90 8.56 7.2 6 4.96 3.6 100 8.32 6.8 5.6 4.64 3.36 110 8.08 6.56 5.28 4.4 3.2 200 6.48 4.48 3.36 2.64 1.84 300 5.12 3.28 2.4 1.92 1.36 400 4.16 2.56 1.84 1.52 1.04 500 3.52 2.16 1.6 1.2 0.96 600 3.12 1.84 1.36 1.12 0.8 700 2.72 1.68 1.2 1.04 0.72 800 2.4 1.52 1.04 0.96 0.72 900 2.24 1.36 0.96 0.8 0.72 1000 2 1.28 0.96 0.72 0.64

113

0

2

4

6

8

10

12

0 200 400 600 800 1000 1200

Resistance in K Ohms

Pk-P

k Vo

ltage

(V)

50 HzHT

100 HzHT

150 HzHT

200 HzHT

300 HzHT

Figure-4.24 Effect of resistance at Pk-Pk voltage at various frequencies and at temperature 1600C

Table-4.24: Difference in voltage for each 100kΩ band at 1600C

Frequency(Hz) 50Hz 100Hz 150Hz 200Hz 300Hz Resistance(kΩ) Pk-Pk(∆V) Pk-Pk(∆V) Pk-Pk(∆V) Pk-Pk(∆V) Pk-Pk(∆V) 1-100 1.88 3.4 4.6 5.56 6.84 100-200 1.84 2.32 2.24 2 1.52 200-300 1.36 1.2 0.96 0.72 0.48 300-400 0.96 0.72 0.56 0.4 0.32 400-500 0.64 0.4 0.24 0.32 0.08 500-600 0.4 0.32 0.24 0.08 0.16 600-700 0.4 0.16 0.16 0.08 0.08 700-800 0.32 0.16 0.16 0.08 0 800-900 0.16 0.16 0.08 0.16 0 900-1000 0.24 0.08 0 0.08 0.08

Table 4.24 describes the change in Pk-Pk voltage for each 100 K ohm resistance band. It

is clear from the data obtained that PZT is temperature sensitive for particular frequency

and resistance range. For example at room temperature the Pk-Pk voltage was 1.4 V at 50

Hz and 1-100 K ohm resistance range. For the same resistance range (1-100K ohm) at

1600C and 50 Hz, the vale noted is 1.88 V. For the same resistance range and at 300 Hz

114

the value changes from 5.72V (at 200C) to 6.84V (at 1600C). The change in voltage for

each resistance band at different frequencies has been shown in Figure. 4.25.

0

1

2

3

4

5

6

7

8

1 2 3 4 5 6 7 8 9 10

Resistance band

Pk-P

k Vo

ltage

(V)

50Hz100Hz150Hz200Hz300

Figure 4.25 Change in Pk-Pk voltage for each 100kΩ band at 1600C

Figures 4.26 to 4.30 show the difference for Pk-Pk voltage between two referenced

temperatures. It is clear from these curves that output voltage at 1600C is always less as

compared to room temperature values. With lesser value of resistance, the output voltage

is high enough and then continuously it is in decreasing order. The gap between two

curves is minute which describe that temperature chance doesn’t effect too much for

ordinary conventional equipments. However this change is highly effective for sensitive

equipments in which these smart materials being used. Therefore care must be taken for

selecting the range of considered variables for the reliability of equipments.

115

0

2

4

6

8

10

12

0 200 400 600 800 1000 1200Resistance in K ohms

Pk-P

k Vo

ltage

in V

olts

At 160CAt 20C

Figure 4.26 Effect of temperature on Pk-Pk Voltage at frequency 50 Hz against change in Resistance

0

2

4

6

8

10

12


Pk-P

k Vo

ltage

in V

olts

At 160CAt 20C

Figure 4.27 Effect of temperature on Pk-Pk Voltage at frequency 100 Hz against change in Resistance.

116

0

2

4

6

8

10

12

0 500 1000 1500Resistance in K ohms

Pk-P

k Vo

ltage

in V

olts

At 160 CAt 20 C


0

2

4

6

8

10

12


Pk-P

k Vo

ltage

in V

olts

At 160CAt 20C


117

0

2

4

6

8

10

12


Pk-P

k vo

ltage

in V

olts

At 160 HzAt 20C


118

4.6.5 Development of a Model

The conversion from mechanical force to electrical signals and from electrical signals to

mechanical excitation can easily be transferred by using piezoelectric materials. The

magnitude of transferring the output is a critical parameter in function output of piezo

devices. Various typical models have been developed and optimized by various

researchers. Butterworth-Van Dyke circuit based on IEEE standard on piezoelectricity

and Manson’s electrical network circuit are two of them [89]. These models have their on

limitations and operating ranges. Sherrit et al [90] proposed another model having the

comparison of previously existed models in thickness mode. There was a very little work

on the effect of frequency and magnitude of input voltage and this area was explored by

Georgiou et al [91] by considering the experimental and theoretical assessments on PZT.

The proposed model addressed the other parameters to demonstrate the effect of

resistance, frequency and temperature on the functional performance in the form of Pk-Pk

voltage. In contrast to the Georgiou model, the existing findings demonstrate the effect of

resistances on the output voltage at various resistance bands from 1kΩ to 1000kΩ

resistance bands.

By considering the data obtained in phase-3 of the experimentation, an exponential model

has been developed which indicates the effect of frequency and resistance band on peak-

peak voltage change (∆V) at two different temperatures.

Data tabulated in Table. 4.21 and 4.24 has been used to draw the exponential curves

between resistance band number and difference in peak-peak voltage at 200C and at

1600C for five selected frequencies. These exponential curves at temperature values have

been shown in Figures 4.31-4.35. Pk-Pk value showed a decreasing exponent trend with

119

the increase in resistance band number. By considering the coefficients A and B,

exponents are drawn against Frequency f in Hz. The coefficients A and B against these

frequencies at 200C and showing an increasing trend indicated in Figure 4.36 and Figure

4.37. Similarly the trend for the exponent at 1600C has been shown in Figures 4.38-4.42.

Their coefficients A and B have been drawn against frequency and shown in Figures 4.43

& 4.44.

An exponential model developed indicating the effect of resistance band number (N) on

peak-peak voltage at 200C and 1600C is as under,

V∆ = BNAe−

Where feA 0035.018.2= and feB 003.023.0= (At 200C)

feA 003.074.2= and feB 003.027.0= (At 1600C)

∆V = is the difference in Pk-Pk voltage at particular resistance band.

N = Resistance band number.

At Room Temperature (200C)

∆V = 2.3378e-0.2501N

R2 = 0.9696

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

1 2 3 4 5 6 7 8 9 10

Resistance Band Number,N

Peak

-Pea

k Vo

ltage

(∆V)

Expon. (50Hz)

Figure. 4.31 Difference in Pk-Pk value against Resistance band number at 50Hz

120

∆V = 3.3779e-0.3352N

R2 = 0.9687

0

0.5

1

1.5

2

2.5

3

1 2 3 4 5 6 7 8 9 10


Peak

-Pea

k Vo

ltage

(∆

V)

Expon. (100Hz)


∆ V = 4.1737e-0.4122N

R2 = 0.9478

0

0.5

1

1.5

2

2.5

3

3.5

4

1 2 3 4 5 6 7 8 9 10


Peak

-Pea

k Vo

ltage

(∆

V)

Expon. (150Hz)


121

∆ V = 4.4656e-0.4604N

R2 = 0.9441

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

1 2 3 4 5 6 7 8 9 10


Peak

-Pea

k Vo

ltage

(∆

V)

Expon. (200Hz)


∆V = 6.2123e-0.6048N

R2 = 0.9506

0

1

2

3

4

5

6

7

1 2 3 4 5 6 7 8 9 10


Peak

-Pea

k Vo

ltage

(∆V)

Expon. (300Hz)


122

A = 2.1827e0.0036f

R2 = 0.9409

01234567

0 100 200 300 400Frequency, f (Hz)

Coe

ffic

ient

A

Expon. (A)

Figure. 4.36 Exponential coefficient, A against Frequency in Hz at 200C

B = 0.2296e0.0034f

R2 = 0.9613

00.10.20.30.40.50.60.7

0 100 200 300 400

Frequency, f (Hz)

Coe

ffic

ient

B

Expon. (B)

Figure 4.37 Exponential coefficient, B against Frequency in Hz at 200C

123

At 1600C

∆V = 2.7586e-0.2785N

R2 = 0.9459

0

0.5

1

1.5

2

2.5

0 2 4 6 8 10 12


Peak

-Pea

k Vo

ltage

(∆

V)

Expon. (50Hz)


∆V = 4.164e-0.4077N

R2 = 0.9604

0

0.5

1

1.5

2

2.5

3

3.5

4

0 2 4 6 8 10 12


Peak

-Pea

k Vo

ltage

(∆

V) Expon. (100Hz)


124

∆V = 5.1224e-0.4966N

R2 = 0.9232

0

0.5

1

1.5

22.5

3

3.5

4

4.5

5

0 2 4 6 8 10 12


Peak

-Pea

k Vo

ltage

(∆

V)

Expon. (150 Hz)


∆V = 3.4694e-0.4427N

R2 = 0.7944

0

1

2

3

4

5

6

0 2 4 6 8 10 12


Peak

-Pea

k Vo

ltage

(∆

V)

Expon. (200Hz)


∆V = 6.6136e-0.7014N

R2 = 0.8639

0

1

2

3

4

5

6

7

8

0 2 4 6 8 10 12

Resistance Band Number

Peak

-Pea

k Vo

ltage

(∆

V)

Expon. (300Hz)

Figure.4.42 Difference in Pk-Pk value against Resistance band number at 300Hz

125

A = 2.7351e0.0027f

R2 = 0.5975

01234567

0 100 200 300 400

Frequency, f (Hz)

Coe

ffic

ient

A

Expon. (A)

Figure-4.43 Exponential coefficient, A against Frequency in Hz at 1600C

B = 0.2659e0.0032f

R2 = 0.8603

0

0.2

0.4

0.6

0.8

0 100 200 300 400

Frequency, f (Hz)

Coe

ffic

ient

B

Expon. (B)

Figure-4.44 Exponential coefficient, B against Frequency in Hz at 1600C

The results presented in above stated figures 4.36, 4.37 and 4.43, 4.44 clearly indicate the

same behavior in exponential form but the sensitivity for both case is prominent. This

sensitivity is very much dependent on resistance change as compared to frequency and

temperature change. Model has been validated with repeatability and it can be modified

by changing the magnitudes of existing values for wide range of applications.

126

4.7 Discussions

The objective of the present work was to explore the unattended characteristics of

thin lead zirconate titanate piezoelectric ceramics disc during thermal cycling/shocking.

Thermal cycling at different water conditions in various environments has been carried

out. Where as the thermal shocking has been done in de-ionized water. Qualitative

extensive data has been obtained by tedious and lengthy experiments by using the reliable

instrumentations. The aim was to analyze the change in critical properties of above stated

material on its functioning and output performance. Three types of experimentation, each

having its own importance in exploring the properties of PZT material have been

conducted. Frequency of maximum impedance and frequency of minimum impedance of

piezoelectric ceramics material is an important measuring criterion for calculating the

other piezoelectric parameters, like coupling factors, and mechanical quality factor Q.

Significant findings are presented in the subsequent sections.

4.7.1. Effect of Water on PZT Disc

There are many engineering applications where mechanical vibrations convert to

electrical signals. Piezoelectric crystals generate ultrasonic waves in solids and detect

these mechanical waves. The piezoelectric crystals excited by an ac source generate

ultrasonic waves at certain frequencies and converted to electrical signals and can be

displaced on oscilloscope.

A lead zirconate titanate (PZT) ceramics disc was used to investigate the performance

characteristics when exposed to three different solutions; ordinary water, de-ionized

water and a solution of NaCl. The PZT was subjected to thermal cycles in the solutions at

127

800C and changes in the peak to peak voltages were observed.. The change in voltage

may affect the actuating and sensing capability of the instrument in which they are used.

The present work consist a qualitative data to design the smart structures used under such

applications. By considering the above discussion, it is concluded that PZT thin disc is

sensitive in performance characteristics in various solutions at different frequencies. The

changes in potential across the PZT ceramic can be attributed to the out put functional

performance of the ceramic in different water conditions.

4.7.2. Thermal Cycling/Shocking of Thin PZT Disc [From 1000C (Thermal

chamber) to 200C (In de-ionized water)]

Thermal shocking is one of the major causes of degradation of piezoelectric materials. A

thin lead zirconate titanate disc has been analyzed during thermal shocking from 1000C to

200C in de-ionized water. Dielectric constant and coupling factor has been measured by

using the capacitance and frequency of maximum and minimum impedance values

obtained by precise instrumentations. Resonance and anti resonance frequencies are the

measure of electromechanical coupling factor. The coupling between the electrical

excitation and mechanical vibrations determine its piezoelectric effect. Mechanical

vibrations appears like a series LCR circuit to the ac source. This LCR circuit has

minimum impedance at certain frequency and is called resonance frequency. This LCR

circuit has another frequency on the other end which is at maximum impedance and is

called anti-resonance frequency. An extensive study and analysis have been taken in

thermal shocking of PZT disc. The behavior of change in capacitance value is frequency

dependent. The measurement taken at 1 KHz shows no remarkable change in its

128

capacitance value, where as the values obtained at frequency of maximum and at

frequency of minimum impedance showing a remarkable change in its capacitance,

impedance and dielectric values. The capacitance value decreasing continuously by

thermal shocking at fm and a reverse effect is at fn. Dielectric constant at fm decreases by

increasing number of shocks and is an expected normal behavior. Thermal shocking

changes dipole length and causes re-orientations of these dipoles which attributes to the

changes in capacitance and dielectric constant of the material. Effective and transverse

coupling factors are continuously increasing. The difference in frequency of maximum

and minimum impedance is widening throughout which resulted in an increases of

coupling factor. This increase in coupling factor is thought to be due to lesser shocking

temperature difference. Further experimentation is recommended with high temperature

difference in thermal shocking. The properties of the materials degrade with the change

in environment. Earlier studies described that piezo material are temperature and

frequency sensitive. The critical temperature where these piezo properties should change

is the curie temperature, but it is observed in present work that thermal shocking is a

severe cause of the degradation of these properties even well below the curie temperature.

The description of dielectric constant is very difficult in thermal cycling problems

because the orientations of molecular size dipoles changes frequently in such shocking

conditions. Theory becomes more difficult because of electrostatic interaction between

dipoles. However, the measurement of fm and fn is one of the reliable methods to

determine the capacitance value at particular frequency. The relative difference in the

frequencies of maximum and minimum impedance depends on both the material coupling

factor and resonator geometry.

129

Effective ionic size and the forces in ceramics crystals are temperature dependent and

may change a particular temperature to a new structure. The small ionic movement is

capable of change in properties of the piezocrystals. Change in dimension occurs due to

thermal cycling/ shocking and resulted in change in ionic size orientation of dipoles.

Piezoelectric undergoes a spontaneous displacement of ions below the curie temperature

due to thermal cycling and elongate the basic structure. The polarization direction may

alter the properties of the piezoelectric ceramics. The development of the parameter

dipole moment involves long range interaction energy lower by re-arrangement of these

ions. When the temperature difference increase the ions become shifted, which change its

polarization. This change in polarization further causes of degradation in capacitance and

dielectric properties of the material.

Increase in dielectric constant at 1 KHz is very less as compared to the decrease in its

value at frequency of maximum impedance. The increasing value of transverse and

longitudinal coupling factor is a an interesting finding and it is observed that the thermal

shocking in de ionized water increase the capability of converting electrical energy to

mechanical energy and vise versa. This effect may useful in designing of oscillators and

sensors.

130

4.7.3 Thermal Cycling/Shocking of Thin PZT Disc from 1000C&1500C (Thermal

chamber) to 200C (In de-ionized water)

This part of the work was done to analyze the sensitivity of thin PZT in thermal

shocking at two different temperatures. The tests conducted at 200C and 1600C and a

comparative analysis have been conducted to investigate the effect of temperature on

piezoelectric properties. Values for dielectric constant, coupling factor and modulus of

impedance are greatly affecting with the number of cycle as well as by changing the

shocking conditions.

The change in fm and fn causes the change of mechanical quality factor. This response of

the material can be utilized in designing of oscillators. It is observed that the difference in

these two stated frequencies (fm & fn) is small as compared to their impedance peaks

during thermal shocking. The results suggest that the PZT ceramic suffers a noticeable

change in polarization when exposed to repeated heating and quenching cycles well

below the curie temperature (350oC) for the PZT ceramic. It is thought that significant

depolarization of the PZT ceramic occurs due to the disorientation of the ferroelectric

domains and this re-orientation is affecting the critical piezoelectric properties by thermal

shocking and quenching. The behavior is normal but the number of peaks has been

increased due to expected change in length and the re-orientation of the dipoles. The

development of the dipole moments by thermal shocking is due to the interaction

between the ions in the unit cells of the crystal geometry. When these ions displaced, the

energy of the crystals decreases. This decrease in energy and ionic movement displace

the dipole moment and may result in the form of piezoelectric crystals degradation in its

properties. At fm, the PZT crystals can be used as filters with high mechanical quality

131

factor. Between fm and fn the response controlled by the mass of the crystal. This property

can be utilized in the designing of oscillators. Higher is the difference between these two

frequencies, higher is the coupling factor. This increase in coupling factor is a measure of

the efficiency of converting mechanical energy to electrical energy and and electrical

energy to mechanical energy.

4.7.4. Effect of Frequency and Resistance on peak-peak voltage in Thermal

Conditions

A long series of experimentations have been performed in this phase. The effect

of frequency and resistance has been observed for the output voltage across the thin PZT

disc. By observing the results, it can be stated that thin PZT disc is relatively less

sensitive in its output performance at two different temperature conditions (i.e..1600C

&200C). For both conditions, the peak-peak voltage value was higher at lower

frequencies but interestingly, the difference in peak-peak voltage for a particular

resistance band behaved differently. At a particular resistance band and frequency for two

temperatures, the change in voltage indicates that temperature also influencing the

performance characteristics of thin disc. At higher frequencies, the maximum drop in

voltage was observed at low resistance as compared to at low frequency drop. Another

interesting behavior observed that after 400 KΩ resistances the peak-peak voltage

observed is approximately constant even at higher frequencies. The model developed in

section 4.5.5 indicates very useful results those can be utilized for the modeling of smart

piezoelectric devices working in these particular ranges. Model shows that PZT disc is

relatively temperature sensitive and the coefficient values are frequency dependent.

132

CHAPTER #5

CONCLUSIONS AND FUTURE RECOMMENDATIONS

5.1 Conclusions

Fatigue behavior of piezoelectric materials either by electrical, mechanical,

electromechanical or thermal cycling /shocking is still a field of recent research. Analysis

of these smart materials has a great scope for further research in many directions. The

current research work is a unique finding and effort in the field of piezoelectric materials

under thermal cycling condition. In literature review section importance and need of

work has been elaborated

The study shows that the performance characteristics are sensitive to the type of solution

in which the PZT was immersed. The drop in potential in heating cycle is greatest in

NaCl solution followed by ordinary tap water and least in de-ionized water. The time in

regaining the peak to peak voltage was longer by the NaCl solution followed by de-

ionized water and then the least time was observed in ordinary tap water. These changes

are thought to be attributed to the presence of ions and solid residue which adheres to the

surface of the PZT ceramic and evaporate during the drying stage after a specific time

depending on frequency of excitation.

The work indicates the effect of thermal shock and quenching in de-ionized water and the

degradation in piezoelectric thin PZT disc. Thermal shocking is one of the severe causes

for the change in dipole lengths and directions which changes its capacitance and

dielectric constant values. All measured values can be used to calculate the other

piezoelectric parameters and Mechanical Q factor for the piezo specimens.

133

During thermal shocking, the decrease in energy and ionic movement displace the dipole

moment and may result in the form of piezoelectric crystals degradation in its properties.

At fm, the PZT crystals can be used as filters with high mechanical quality factor.

Between fm and fn the response controlled by the mass of the crystal. This property can be

utilized in the designing of oscillators.

The model developed in section 4.5.5 indicates very useful results those can be utilized

for the modeling of smart piezoelectric devices working in these particular ranges. In this

model it is concluded that thin PZT disc is relatively more sensitive in resistance change

as compared to temperature and frequency change.

134

5.2 Future Recommendations

1. Thermal cycling of piezoelectric specimens has been determined in various water

condition and their affects on performance characteristics are noticeable in

previous findings. On the basis of these findings, following future

recommendations are noted as:

• To check the performance characteristic on other grades and sizes of the

piezoelectric materials.

• To investigate the behavior at higher temperature rather than the lower as

considered in present work.

• To determine the behavior in other designed circuits at higher frequencies.

• To investigate the sensitivity analysis and optimization by using the

standard techniques.

• To perform the experimentation by considering the other environments

and solutions.

2. There are many engineering applications where mechanical vibration converts to

electrical signals. Thermal shocking in de ionized water shows very informative

and important results and there is a great scope of work in this area as under.

• To investigate the various piezoelectric parameters at higher thermal

shocking temperature.

• To investigate the stress corrosion cracking of piezoelectric ceramics in

water.

• Interaction and reliability of electromechanical coupling in water and air.

135

• Investigations are recommended at above or near to curie temperature.

• Affect of impedance, dielectric loss, and other compliances are required to

investigate for further measurements and characteristics of these materials.

• Determination of stress intensity factor by using fracture mechanics

techniques.

• Modeling and designing of equipments is recommended to investigate the

performance characteristics and sensitivity by using available commercial

software’s for reliability and validation of electromechanical systems.

• Affect of properties on PZT by variation of temperature from very low to

high is another area, which is under investigation and may be useful for

numerous sophisticated applications.

• Material characteristics are key factor in material selection of electronic

equipments. Most components are required with their high dielectric

constant. Before selection of particular grade and size of piezoelectric

material, it is recommended to select the optimized frequency and

temperature for maximum performance output.

3. To develop a center of study for the analysis of electronics and smart materials

used in micro electro-mechanical systems in Mechanical Engineering Department

University of Engineering and Technology Taxila.

136

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674

APPENDIX-A

THERMAL CYCLING/SHOCKING RESULTS IMAGES OF THIN PZT DISC

Testing/Measurements Following testing were measured in thermal shocking test

1. Thermal shocking from 1000C from thermal chamber to de-ionized water at 200C. 2. Thermal cycling test between 1000C and 900C for 60 cycles in step of 10 cycles.

3 Shocked once for 60Cycles between 1000C and 900C 4. Thermal shocking from 1500C from thermal chamber to de-ionized water at 200C.

All of the above enlisted tests were performed and tested specimens were analyzed by using impedance analyzer along with test fixture. The figures below shows behavior of thin PZT disc during above stated testing in the form of capacitance, Impedance, Dissipation factor and Phase angle in different conditions.


A-1 Original value of Capacitance (Cp) of thin disc at 1 KHz

A-2 Original value of Impedance (Z) at 1 K Hz

A-3 Original value Cp atFrequency of Maximum Impedance (fm)

A-4 Original value of Cp at Frequency of Minimum Impedance (fn)

A-5 Original value of Impedance (Z) at Frequency of maximum

impedance

A-6 Original value of Z at Frequency of Minimum Impedance

TEST-1 After Five Shocks A-7 Cp at Frequency of Maximum Impedance

A-8 Cp at Frequency of Minimum Impedance

A-9 Impedance at fm

A-10 Impedance at fn

TEST-4 After Twenty Shocks A-11 Cp at 1 KHZ

A-12 Z at 1 KHz

A-13 Cp at fm

A-14 Cp at fn

A-15 Z at fm

A-16 Z at fn

TEST-5 After Twenty Five Shocks A-17 Cp at 1 KHz

A-18 Z at 1 KHz

A-19 Cp at fm

A-20 Cp at fn

A-21 Z at fm

A-22 Z at fn

TEST-6 After Thirty Shocks A-23 Cp at 1 KHz

A-24 Z at 1 KHz

A-25 Cp at fm

A-26 Cp at fn

A-27 Z at fm

A-28 Z at fn

TEST-7 After Thirty Five Shocks A-29 Cp at 1 KHz

A-30 Z at 1 KHz

A-31 Cp at fm

A-32 Cp at fn

A-33 Z at fm

A-34 Z at fn

2. Thermal cycling test between 1000C and 900C for 60 cycles in step of 10 cycles.

In this series of experimentations, the PZT discs were observed for their sensitivity analysis during thermal cycling to observe their stepped thermal cycling and continuous thermal cycling between very narrow ranges of thermal change. The specimens were heated to 1000C and then cycled between 1000C and 900C for ten cycles. The discs were then taken to measure their capacitance and impedance values as described in their relative figures. Values measured after every ten such cycles and total 60 cycles were analyzed in a step of ten cycles.

A-35 Original values of Cp at 1 KHz

A-36 Original value of Z at 1 KHz

Test-1 From 1-10 cycles between 1000C and 900C. A-37 Cp at 1 KHz (1-10 continuous cycles)

A-38 Z at 1 KHz (1-10 continuous cycles)

A-39 Cp at fm (1-10 continuous cycles)

A-40 Cp at fn (1-10 continuous cycles)

A-41 Z at fm

A-42 Z at fn

Test-2 From 10-20 cycles between 1000C and 900C. A-43 Cp at 1 KHz (10-20 continuous cycles)

A-44 Z at 1 KHz (10-20 continuous cycles)

A-45 Cp at fm

A-46 Cp at fn

A-47 Z at fm

A-48 Z at fn

Test-3 (21-30 cycles between 1000C and 900C)

A-49 Cp 1 KHz

A-50 Z at 1 KHz

A-51 Cp at fm

A-52 Cp at fn

A-53 Z at fm

A-54 Z at fn

Test-4 (31-40 cycles) A-55 Cp at 1 KHz

A-56 Z at 1 KHz

A-57 Cp at fm

A-58 Cp at fn

A-59 Z at fm

A-60 Z at fn


A-62 Z at 1 KHz

A-63 Cp at fm

A-64 Cp at fn

A-65 Z at fm

A-66 Z at fn


A-68 Z at 1 KHz

A-69 Cp at fm

A-70 Cp at fn

A-71 Z at fm

A-72 Z at fn

3. Shocked once 0Cycle-60Cycles A-73 Cp at 1 KHz

A-74 Z at 1 KHz

A-75 Cp at fm

A-76 Cp at fn

A-77 Z at fm

A-78 Z at fn


After Five Shocks

A-79 Cp at 1 KHz

A-80 Z at 1 K Hz

A-81 Cp at fm

A-82 Z at fm

A-83 Z at fn

After Fifteen Shocks A-84 Cp at 1 KHz

A-85 Z at 1 KHz

A-86 Cp at fm

A-87 Cp at fn

A-88 Z at fm

A-89 Z at fn

After Twenty Five Shocks A-90 Cp at 1 KHz

A-91 Z at 1 KHz

A-92 Cp at fm

A-93 Cp at fn

A-94 Z at fm

A-95 Z at fn

After Thirty Five Shocks A-96 Cp at 1 KHz

A-97 Z at 1 KHz

A-98 Cp at fm

A-99 Cp at fn

A-100 Z at fm

A-101 Z at fn

Appendix-B

List of Pertinent PhD Publications

1. Riffat Asim Pasha, M.Z.Khan, “Recent Developments in Piezoelectric Ceramics Materials and Deteriorations of their Properties” Proceedings of 2nd International Conference on Frontiers of Advanced Engineering Materials (FAEM-2006) pp. 13-19.

2. Riffat Asim Pasha, M.Z.Khan, A.M.Hashmi, “Experimental Procedure of

Frequency Determination in Piezoelectric Ceramics Materials, Al-Azhar University Engineering Journal, Vol.2, No. 4. pp. 380-388 (AEIC- 2007) Cairo, Egypt.

3. Riffat Asim Pasha Zahid Suleman and M. Z. Khan, “Analysis of Thickness Effect

on Piezoelectric Beam” Proceedings of Failure of Engineering Materials and Structures, pp. 59-63 (FEMS-2007)

4. Riffat Asim Pasha, M.Z.Khan, “Thermal Shocking of a Thin Lead Zirconate

Titanate Piezoelectric Ceramics disc, Proceedings Pakistan Academy of Science, 46(1): pp. 47-52 2009 (HEC Recognized).

5. Riffat Asim Pasha, M.Z.Khan, “Performance Characteristics of a Lead Zirconate

Titanate Piezoelectric Ceramic Disc in Water, Accepted for publication in M.U Research Journal of Engineering and Technology, 2009 (HEC Recognized).

6. Riffat Asim Pasha, Muhammad Zubair Khan, “Effect of Thermal Shocking and

Quenching on the Degradation Behaviour of a Thin PZT Disc, Pakistan Journal of Scientific and Industrial Research,2010 53(1) p. 1-5 (HEC Recognized)

web.uettaxila.edu.pk · ii FATIGUE BEHAVIOR OF PIEZOELECTRIC CERAMICS MATERIAL Author Riffat Asim Pasha 03-UET/PhD-ME-03 A dissertation submitted in partial fulfillment of the requirements

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