Definition of ceramics

1.

Background of ceramics
Definition of ceramics
Kyu Hyoung Lee

2.

Definition of ceramics
Metals
- consist of atoms held together by delocalized electrons
- overcome the repulsion between ion cores
- Pure : Many main-group / Transition & inner transition elements
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3.

Definition of ceramics
Metals
- Alloys : combinations of metallic elements or metallic and
nonmetallic elements
- Delocalized electrons characteristic properties
High electrical conductivity
High electrical conductivity
- Close packed structures deform plastically at room temperature
Metallic bonding Not directional
Lower bond energy Small nearest neighbor distance
Electron cloud shield cores
SC / BCC / FCC / HCP

4.

Definition of ceramics
Metals
- SC (Simple Cubic Structure)
Coordination # = 6
a
Atomic Packing Factor (APF)
= Volume of atoms in unit cell / Volume of unit cell
*Hard spheres
1 4/3 π (0.5a)3
APF for a SC =
= 0.52
3
a

5.

Definition of ceramics
Metals
- BCC (Body Centered Cubic Structure)
Coordination # = 8
Cr, W, Fe( ),
Ta, Mo
a
3a
a
2a
2 4/3 π (31/2a/4)3
APF for a BCC =
= 0.68
a3

6.

Definition of ceramics
Metals
- FCC (Face Centered Cubic Structure)
Coordination # = 12
Al, Cu, Au,
Pb, Ni, Pt,
Ag
a
4 4/3 π (21/2a/4)3
APF for a FCC =
= 0.74
a3
ABCABC... Stacking Sequence
A
B
B
C
B
C
C
B
B
B

7.

Definition of ceramics
Metals
- HCP (Hexagonal Close Packed Structure)
Coordination # = 12
A sites
Cd, Mg,
B sites
A sites
APF for a HCP = 0.74
ABAB... Stacking Sequence
c/a = 1.633
Ti, Zn

8.

Definition of ceramics
Ceramics
- consist of arrays of interconnected atoms
- Nonmetallic inorganic solids / All inorganic semiconductors
- Oxides, Nitrides, Carbides, Borides, Silicides, Sulfides, Glass
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9.

Definition of ceramics
Ceramics
- Mixed bonding – a combination of covalent, ionic, (metallic)

10.

Definition of ceramics
Ceramics
- Crystal structures – Oxide structures
Ionic radius of oxygen anion > Ionic radius of metal cation
Close packed oxygen ion in a lattice (FCC)
Cations in the holes
Size relationship cation to anion
Charge neutrality
Crystallographic arrangements
Stoichiometry

11.

Definition of ceramics
Ceramics
- Charge neutrality : Net charge = 0
Composition : Ma+xAb-y a x + (-b) y = 0
NaCl, ZnO, Al2O3, SiO2, Nb2O5, WO3
- Relative sizes of ions : Stable structures
Coordination # increases with rcation/ranion
ㅡ
ㅡ
ㅡ
ㅡ
ㅡ
unstable
ㅡ
ㅡ
+
+
+
ㅡ
ㅡ
ㅡ
stable
ㅡ
ㅡ
stable

12.

Definition of ceramics
Ceramics
rcation
ranion
Coord.
Number
< 0.155
2
ZnS
linear
0.155 - 0.225 3 triangular
0.225 - 0.414 4 tetrahedral
NaCl
0.414 - 0.732 6 octahedral
0.732 - 1.0
8
cubic
CsCl

13.

Definition of ceramics
Ceramics
- Ionic radius : http://abulafia.mt.ic.ac.uk/shannon/
Database of Ionic Radii (Periodic Table)
To view details for a particular element Click on element
Radii for a particular element with
i) charge
ii) coordination number