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
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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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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.
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