High energy Nd-laser irradiation effect on optimally co-doped terbium–neodymium BPSCCO bismuth cuprate superconductor

Physica C 402 (2004) 303–308

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High energy Nd-laser irradiation effect on optimallyco-doped terbium–neodymium BPSCCO bismuth

cuprate superconductor

Morsy M.A. Sekkina, Khaled M. Elsabawy *

Department of Chemistry, HTc-Ceramic Superconductors Unit, Faculty of Science, Tanta University, Tanta, Egypt

Received 7 August 2003; accepted 15 September 2003

Abstract

The optimally co-doped Bi0:8Nd0:1Tb0:1PbSr2Ca2Cu3O10 (with Tc ¼ 108 K) was prepared by the conventional solid

state reaction route. The sample was irradiated by using high energy Nd-laser and exposed to two different doses of

laser beam irradiation. The first was 10 W/cm2 for 60 min and the second was 20 W/cm2 for 120 min. The effect of laser

irradiation on structural, morphological and superconducting properties of optimally co-doped BPSCCO was inves-

tigated showing some structure promotion incorporated with suppressing its superconducting properties.

� 2003 Elsevier B.V. All rights reserved.

Keywords: Laser; Irradiation; X-ray; SEM; Co-doping

1. Introduction

The influence of laser radiation on the charac-teristics of HTSC was studied in some previous

publications [1–8]. However their results are am-

biguous and inconsistent. In general, degradation

of the HTSC-material is observed, but there are

also data showing an increase in the critical cur-

rent [1–6].

Thin ceramic films or powder-sintered ceramic

surface recrystallized with precise control overthickness, structure, orientation of grains and

stoichiometry are highly desirable for applications

* Corresponding author. Fax: +20-40-3350804.

E-mail address: [email protected] (K.M. Elsabawy).

0921-4534/$ - see front matter � 2003 Elsevier B.V. All rights reserv

doi:10.1016/j.physc.2003.09.088

in electronic devices. Surface treatment by infrared

laser beam is effected instantaneously via sequen-

tial thermal processes such as heating, melting,vaporization and molten zone solidification during

rapid cooling [3–5]. Under such thermal condi-

tions, the surface is expected to experience non-

equilibrium state, thereby acquiring totally new

functional properties. The surface of oxide mate-

rials containing many pores, microcracks, insulat-

ing phases and impurities at the grain boundaries

has been modified to achieve significant increase inthe critical current density [9].

Significant increase in critical current density Jchas been reported due to the reduced number of

grain boundaries and increased preferred orienta-

tion of crystal grains at surface layer [10,11]. Such

sintering method does not assist in orienting the

grain uniform to the surface layer and the whole

ed.

304 M.M.A. Sekkina, K.M. Elsabawy / Physica C 402 (2004) 303–308

bulk. Therefore, some authors tried to instanta-

neously melt and recrystallize only the surface

layer of superconducting YBaxSr2�xCu3O7�y and

ferroelectric BaTiO3 ceramic for two selected

samples [11]. This method will be able to eliminate

pores and microcracks but also generates a pref-erential orientation of grains at the surface layer.

For example, an increase in the pinning force is

necessary to improve current density in supercon-

ductors. However, it is not certain if pinning

the distribution in oxide superconductor follows

Bean�s critical state model as in metal supercon-

ductors. In order to understand where the current

was flowing, we prepared samples that are nearlythe same like YBa2Cu3O7�y in material, length and

height but different only in width. The supercon-

ducting current was found to flow only near the

surface of samples [12,13].

In the literature, only a few authors such as in

[14,15] had investigated the effect of laser irradia-

tions on high-Tc superconductors.Luctiv et al. [14] have studied the effect of dif-

ferent kinds of laser (Nd, CO2 and ruby) irradia-

tions on three families of high-Tc superconductorsnamely 123-YBCO, Bi-2212 and Bi-2223 and they

reported that laser irradiations cause an enhance-

ment of critical current density Jc but suppress Tcbecause of fraction volume of the diamagnetism

inside the bulk of superconducting sample de-

creasing.The aim of the present article is to study the effect

of Nd-laser irradiations on the microstructure,

superconducting and structural properties of opti-

mally co-doped neodymium–terbium Bi0:8Nd0:1-

Tb0:1PbSr2Ca2Cu3O10 sample with Tc-offset¼ 108

K BPSCCO system.

2. Experimental

2.1. Sample preparation

Samples of the general formula BiðxþyÞNdxTby-

PbSr2Ca2Cu3O10, where x ¼ y ¼ 0:05, 0.1 and 0.2,

were prepared by the conventional solid state re-

action method and sintering procedure using ap-propriate amounts of Bi2O3, Nd2O3, Tb2(CO3)3,

PbO, SrCO3, CaCO3 and CuCO3, each of purity

>99%. The mixtures were calcined at 800 �C in

compressed O2 atmosphere for 20 h then reground

and pressed into pellets (thickness 0.2 cm, diameter

1.2 cm). Sintering was carried out under oxygen

stream at (780–840 �C) for 40 h. The temperature

was cooled down slowly (20 �C/h) till 500 �C andannealed there for 20 h under oxygen stream,

then the furnace was cooled down slowly to

room temperature. Finally the materials were

kept in vacuum desiccator over silica gel dryer. A

levitation test was thoroughly applied for the

achievement of superconductive phase and hence

superconductivity.

The superconducting properties were measuredfor the whole series. The selection of optimally co-

doped sample was based on the best supercon-

ducting sample (highest Tc one) which was found

to be Bi0:8Nd0:1Tb0:1PbSr2Ca2Cu3O10 (with Tc ¼108 K).

2.1.1. Laser irradiation source

The pellet of the best Tc (108 K) Bi0:8Nd0:1-Tb0:1PbSr2Ca2Cu3O10 was cut into a square with

dimension 0.5 cm· 0.5 cm, then polished carefully

and forwarded to be the target for Nd-pulsed laser

which has the following parameters: wavelength

k ¼ 1:06 lm, pulsed rate s ¼ 10�3 s. The target was

exposed to two different doses of laser beam irra-

diation, the first 10 W/cm2 for 60 min and the

second 20 W/cm2 for 120 min. The irradiation wascarried out in air without any external heating. The

energies of the pulsed Nd-laser were sufficient to

melt the surface and near surface layers homoge-

neously. Scanning electron microscopy (SEM) was

used for monitoring the morphological changes.

2.2. Structural measurements

2.2.1. X-ray diffraction

The X-ray diffraction (XRD) measurements

were carried out at room temperature on the

ground samples using Cu-Ka radiation source and

a computerized Shimadzu diffractometer (Japan).

2.2.2. Scanning electron microscopy

Scanning electron microscopy (SEM) measure-ments were carried out along the ab-plane using

M.M.A. Sekkina, K.M. Elsabawy / Physica C 402 (2004) 303–308 305

small pieces of the prepared samples by using a

computerized SEM camera with elemental analy-

ser unit Shimadzu (Japan).

2.3. Superconductivity measurements

The DC-electrical resistivity of the prepared

materials was measured as a function of temper-

ature using the modified four-probe technique and

the temperature was recorded in the cryogenic

temperature zone down to 30 K using liquid he-

lium refrigerator.

3. Results and discussion

3.1. Structural measurements

3.1.1. X-ray measurements

Fig. 1(a)–(c) displays the X-ray diffraction pat-

terns for Nd-laser non-irradiated and irradiated

sample Bi0:8Nd0:1Tb0:1PbSr2Ca2Cu3O10.The analysis of the corresponding 2h values and

interplanar spacings d (�A) was carried out which

indicated that the X-ray crystalline structure be-

longs mainly to tetragonal crystal (2223) form a ¼b 6¼ c with characteristic peak at 2h value 4.8–5

0 20 40 60

(c) 2nd Laser absorbed dose = 20 W/cm 2

Inte

nsity

( a.

u.)

Two Theta degree

(b)1st Laser absorbed dose = 10 W/cm2

***[002]

* ** * **

** **

* 2223-phase+ (Ca/Sr)2PbO4-phase

+*

+*

(a)Non irradiated sample

Fig. 1. X-ray diffraction patterns for Bi0:8Nd0:1Tb0:1PbSr2Ca2-

Cu3O10 high-Tc superconductor sample: (a) non-irradiated

sample, (b) first laser absorbed dose¼ 10 W/cm2 and (c) second

laser absorbed dose¼ 20 W/cm2.

indexed (0 0 2) as shown in our pattern [16]. The

unit cell dimensions were calculated using the pa-

rameters of most intense X-ray reflection peaks

and found to be a ¼ b ¼ 3:6891 �A and c ¼ 35:3162�A for the optimally co-doped BPSCCO. It was

observed that the lattice parameter is nearly con-stant as Nd-laser dose increases.

The analysis of X-ray patterns proved that the

ratio of 2223-major phase reflection peaks to lead-

rich phase plumbate (Ca2PbO4 impurity phase)

increases as laser irradiation doses increase from

10 to 20 W/cm2 respectively.

Furthermore, one can notice that the most in-

tense reflection peak denoted by the (+) symbol inFig. 1(a) and (b) nearly disappeared after the sec-

ond laser absorbed dose 20 W/cm2, which is be-

cause of the high energy of laser irradiation having

very good thermal effect, and as a result the lead

content inside plumbate begins to sublimize par-

tially after the first laser irradiation dose and

completely after the second laser absorbed dose as

clearly seen from Fig. 1(c), causing disappearanceof plumbate impurity phase peak and conse-

quently raising the purity degree of 2223-phase

which is considered to be one of the most impor-

tant advantages of laser treatment.

3.2. Scanning electron microscopy

Fig. 2(a)–(c) displays the scanning electron mi-croscopy (SEM) images of Nd-laser non-irradiated

and irradiated sample Bi0:8Nd0:1Tb0:1PbSr2Ca2-

Cu3O10.

For non-irradiated co-doped BPSCCO (Fig.

1(a)) it is obvious that the Nd and Tb dopants

actually replace the Bi-site in the crystalline lat-

tice structure with high efficiency at low con-

centration of dopants optimally 0.1 mol% due tothe two dimensional solid state diffusion occur-

ring in this region of dopants with more rate of

conversion: 2212+ 1/2(CuO+Ca2CuO3)fi 2223,

and consequently at dopant conc. Nd¼ 0.1 and

Tb¼ 0.1 mol% the average density of solid so-

lution during preparation is optimum and hence

increases the rate of conversion to form the 2223-

phase [17].Furthermore, the average grain size was calcu-

lated at different spots inside the sample and was

Fig. 2. SE micrographs for Bi0:8Nd0:1Tb0:1PbSr2Ca2Cu3O10 high-Tc superconductor sample: (a) non-irradiated sample, (b) first laser

absorbed dose¼ 10 W/cm2 and (c) second laser absorbed dose¼ 20 W/cm2.

306 M.M.A. Sekkina, K.M. Elsabawy / Physica C 402 (2004) 303–308

found to be in between 0.6 and 1.8 lm and no Nd/Tb atoms were noticed in the grain boundaries

which is considered as good evidence for its

locality inside the crystal structure of BPSCCO

regime.

EDX analysis was performed for the prepared

sample which proved that Nd–Tb is regularly

distributed in good approximation with actual

molar ratios.From Fig. 2(b) it is clear that after the first laser

irradiation dose (10 W/cm2 for 60 min) the mor-

phology of the sample surface begins to have mi-

crocracks. The cracks are found in the direction of

the laser scan with considerable depths that de-

pend on the duration and power of laser used for

irradiation.

EDX analysis performed after the first laser ir-radiation dose (10 W/cm2 for 60 min) indicated

that the ratio of lead content begins to reduce

nearly by 32% which is also emphasized by the

X-ray measurements.

From Fig. 2(c) it is obvious that after the sec-ond laser irradiation dose (20 W/cm2 for 120 min)

the morphology of the sample surface is com-

pletely changed again as a result of melting and

recrystallization caused by induced laser irradia-

tion and begins to coagulate again reducing the

number of cracks. The brittle superconductive

oriented crystal formed under high energy laser

dose was observed in our SE-micrograph as a re-sult of recrystallization. A similar behaviour was

observed by Hotta et al. [15] which fully supports

our results.

3.3. Superconductivity measurements

The DC-electrical resistivity was measured as

a function of cryogenic temperature using thefour-probe terminal technique. Thus Fig. 3(a)–

(c) shows the temperature dependence of electrical

resistivity of the non-irradiated and irradiated

laser sample. It is clear that the critical Tc-offset of

90 100 110 120 130 140 150

0

1

2

3

4

5

Tc-offset = 93 K

Tc-offset = 98 K

Tc-offset = 108 K

(c)

(b)

(a)

Non-irradiated 2223-BPSCCO (After 1st Laser absorbed dose = 10 W/cm2

(After 2nd Laser absorbed dose = 20 W/cm2

Res

istiv

ity (O

hm.c

m )

Temperature K

Fig. 3. DC-electrical resistivity for Bi0:8 Nd0:1Tb0:1PbSr2Ca2-

Cu3O10 high-Tc superconductor sample: (a) non-irradiated

sample, (b) first laser absorbed dose¼ 10 W/cm2 and (c) second

laser absorbed dose¼ 20 W/cm2.

M.M.A. Sekkina, K.M. Elsabawy / Physica C 402 (2004) 303–308 307

the optimally co-doped Nd–Tb superconductor

sample is 108 K for the non-irradiated sample

while the Tc-offset decreases as irradiation powerand duration time increase, 98 and 93 K, respec-

tively.

These data indicate that the best supercon-

ducting sample is the non-irradiated Bi0:8Nd0:1-

Tb0:1PbSr2Ca2Cu3O10, where the ratio enhances

the formation of the superconductive tetragonal

phase.

From these results, it is found that after the firstlaser irradiation dose (10 W/cm2 for 60 min) Tc-offset decreased nearly by �9.2% than for the non-

irradiated sample as a result of lead loss caused by

thermal effect of laser irradiation, whereas Tc-offsetdecreased by 13.88% after the second laser irradi-

ation dose (20 W/cm2 for 120 min), which in our

opinion is due to the partial sublimation of lead

required to form the 2223-phase itself.

4. Conclusion

The pellet of optimally co-doped Bi0:8Nd0:1-

Tb0:1PbSr2Ca2Cu3O10 (Tc ¼ 108 K) was irradiated

by using high energy Nd-laser. It was found that

the Ca2PbO4 impurity phase reduced remarkablyas laser irradiation doses increase from 10 to 20 W/

cm2 respectively. After the second laser irradiation

dose (20 W/cm2 for 120 min) the morphology of

the sample surface is completely changed as a re-

sult of recrystallization caused by induced laser

irradiation and form coagulates brittle oriented

crystal in the direction of laser scan. After the firstlaser irradiation dose (10 W/cm2 for 60 min) Tc-offset decreased nearly by �9.2% than for the non-

irradiated sample as a result of lead loss caused by

thermal effect of laser irradiation, whereas Tc-offsetdecreased by 13.88% after the second laser irradi-

ation dose.

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