Common Ceramic crystal structures Structure Name Structure Type Anion Packing Co-ordination Anion Example no: Cation Sodium Chloride

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CERAMICS

Ceramics comes from Keramikos.

Keramikos means a burnt material

% ionic character =

where XA & XB are Electro negativities

%)100(x

1− e−

(XA −XB )2

4

Atomic bonding is ionic to covalent

Depends on Electro negativity

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Ionic character of ceramics

2

• Bonding:

--Mostly ionic, some covalent.

--% ionic character increases with difference in

electronegativity.

He -

Ne -

Ar -

Kr

-

Xe -

Rn -

Cl 3.0

Br 2.8

I 2.5

At 2.2

Li 1.0

Na 0.9

K 0.8

Rb 0.8

Cs 0.7

Fr 0.7

H

2.1

Be 1.5

Mg 1.2

Sr 1.0

Ba 0.9

Ra 0.9

Ti

1.5

Cr

1.6

Fe

1.8

Ni

1.8

Zn

1.8

As

2.0

C 2.5

Si 1.8

F 4.0

Ca 1.0

Table of Electronegativities

CaF2: large

SiC: small

• Large vs small ionic bond character:• Large vs small ionic bond character:• Large vs small ionic bond character:• Large vs small ionic bond character:

CERAMIC BONDING

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Comprising of Metallic and non-metallic elements

Metallic elements +ve Charge – CATION

Non-metallic elements -ve Charge – ANION

1) Charge Neutrality: Charge in the structure Should be neutral

General form:

CaF2: Ca2+

cation

F-

F-

anions+

Characteristics influence Ceramic Structure Characteristics influence Ceramic Structure Characteristics influence Ceramic Structure Characteristics influence Ceramic Structure

CERAMICS

2) 2) 2) 2) Stability :--Size (or) Radius ratio

Cation size (rc ) < < < < Anion Size (ra)

rcationranion

≤ ≤ ≤ ≤ 1

Stabile structure is form when anions surrounds the

cation has in contact (or) touch.

- -

- -+

unstable

- -

- -+

stable

- -

- -+

stable

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Coordinate number : Number of anions nearest to cation

Coordinate number

depends on radius ratio

Size of the ion depends on :

1) Coordinate number

2) Charge on ion

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Cation Site Size• Determine minimum rcation/ranion for C.N. = 6

a = 2ranion

2ranion + 2rcation = 2 2ranion

ranion + rcation = 2ranion rcation = ( 2 −1)ranion

2ranion + 2rcation = 2a

4140anion

cation .r

r=

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� For CN=8

Are equal

=> Crystal Structure

NaCl

R. Ratio = 0.563

(0.414 to 0.732)

CN = 6

Octahedral

Other Eg: MgO, LiF, FeO

Ceramic Systems

FCC (Interpenetrating)

Nacl or Rock salt structure

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CsCl

R. Ratio = 0.9392

(0.732 to 1 )

CN = 8

Not BCC : Cubic

Cesium Chloride structure

ZnS

R. Ratio = 0.4021

(0.225 to .414)

CN = 4

Tetrahedral

Other Ceramics : MnS, SiC, ZnTe

Zink Blend or Sphalerite

FCC anion

Tetrahedron cationes

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4

rcationranion

Coord #

< .155

.155-.225 .225-.414 .414-.732

.732-1.0

ZnS (zincblende)

NaCl (sodium chloride)

CsCl (cesium chloride)

2

3 4 6

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COORDINATION AND IONIC RADII

If Charge on iones are not same Crystal Structure

AX2= CaF2

R. Ratio = 0.75

(0.732 to 1)

CN = 8

Other Ceramics :

ZrO2, UO2, PuO2, ThO2

Fluorite Structure

Anion (F) corners

Cation (Ca) cube center

Similar to CsCl

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Crystal Structure

More than 1 Cation

BaTiO3

Perovskite Structure

ABX3

Other Ceramics : CuFeS2

Structure

Name

Structure

Type

Anion

Packing

Co-ordination

no: Cation

Anion Example

Sodium

Chloride

AX FCC 6 6 Nacl,

MgO,Feo

Cesium

Chloride

AX Simple

Cubic

8 8 CsCl

Zink Blend

(Sphalerite)

AX FCC 4 4 ZnS, SiC

Fluorite

Structure

AX2 Simple

Cubic

8 4 CaF2,

ZnS

Perovskite ABX3 FCC 12(A) , 6(B) 6 BaTiO3

Common Ceramic crystal structures

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(111) Plane in FCC- NaCl

Each anion share

1 Octahedral 2 tetrahedral Positions

• • • • On the basis of ionic radii, what crystal structureOn the basis of ionic radii, what crystal structureOn the basis of ionic radii, what crystal structureOn the basis of ionic radii, what crystal structure

would you predict for FeO? would you predict for FeO? would you predict for FeO? would you predict for FeO?

Cation

Al3+

Fe2+

Fe3+

Ca2+ Anion

O2-

Cl-

F-

Ionic radius (nm)

0.053

0.077

0.069

0.100

0.140

0.181

0.133

• Answer:

based on this ratio,based on this ratio,based on this ratio,based on this ratio,

--------coord # = 6coord # = 6coord # = 6coord # = 6

--------structure = NaClstructure = NaClstructure = NaClstructure = NaCl

EX: PREDICTING STRUCTURE OF FeO

rcation

ranion

=0.077

0.140

= 0.550(0.414 to 0.732)

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4.35] in BeO Be2+ = 0.035 nm a) Interstitial site “Be” occupies ?

b) Fraction of sites occupied by Be ?

Note : Each onion spear having one octahedral

and 2 Tetrahedral sites exists in crystal.

Ceramic Density Computation

A

AC

NV

)AA(n

C

Σ+Σ′=ρ

Number of formula units/unit cell

Volume of unit cell

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4.38) Calculate theoretical Density of NiO if it is

a rock salt structure

4.32

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Carbon Forms� Polymorphic form and amorphous form

� Not fall any type

Carbon Phase diagram

Carbon Forms - Graphite• layer structure – aromatic layers

– weak van der Waal’s forces between layers

– planes slide easily, good lubricant

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Layered Structure

Unit cell

�Electrodes in Electric Furnaces.� Rocket Nozzles.� Refractories.

• Diamond

– tetrahedral carbon

• hard – no good slip planes

• brittle – can cut it

– large diamonds – jewelry

– small diamonds

• often man made - used for

cutting tools and polishing

– diamond films

• hard surface coat – tools, medical

devices, etc.

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Synthetic diamond

� HTHP

� Chemical Vapor Deposition (CVD)

� Large & Natural Diamonds

Rough Diamonds

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Precession Diamond

Carbon Forms –

Fullerenes, Nanotubes, Graphene

• Fullerenes or carbon nanotubes or graphene

– wrap the graphite curving into ball or tube or sheets

Buckminister fullerenes

• Like a soccer ball C60

FullerenesBuckyBall

0 D

C – Nanotubes

1 DGraphene

2D

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Andre Geim Konstantin Novoselov

The Nobel Prize in Physics 2010

Invention of “graphene" two-dimensional material

Graphene is stronger and stiffer than diamond, yet can be stretched by a

quarter of its length, like rubber. Thinnest substance in the known universe

can be use for high tech application such as computing, consumer

electronics, "green" energy technology and engineering.