Material Science 2

 

Crystal Structure

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Crystal Structure

A brief detail with examples

Co-rdination Number

Formula units per unit Cell

NaCl  Type
Rock-Salt

Na+ ions occupy the Octahedral sites while Cl ions are in ccp arrangement or vice versa eg. NH4Cl, AgCl, AgBr, Halides of Li, Na &Rb; CaC2 etc.

Na+ = 6

Cl = 6

4

CsCl Type

Cs+ ions occupy cubic sites while Cl ions are at the corners of a cube or vice versa.

Cs+ = 8

Cl = 8

1

CaF2 
Type Fluorite Structure

Ca2+ ions are in ccp while F ions occupy Tetrahedral sites e.g. CaF2, BaF2, BaCl2, SrF2 etc.

Ca2+ = 8

F = 4

4

ZnS-Type

a) Zinc blende

Zn2+ ions occupy Alternate tetrahedral sites e.g. while S2- ions are in the ccp e.g. ZnS, CuCl, CuBr,CuI, AgI etc.

Zn2+ = 4

S2- = 4

4

b) Wurzite

Zn2+ ions occupy Alternate tetrahedral sites while S2- ions are in hcp type of arrangement.

Zn2+ = 4

S2- = 4

4

Antifluorite
Structure
Na2O

Positive ions occupy all the tetrahedral sites while Negative ions are in ccp type of arrangement. e.g. Na2O

Na+ = 4

O2- = 8

4

 Solid State Page 3