Material Science 2

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 S^2- ions are in the ccp e.g. ZnS, CuCl, CuBr,CuI, AgI etc.

Zn²⁺ = 4

S^2- = 4

4

b) Wurzite

Zn²⁺ ions occupy Alternate tetrahedral sites while S^2- ions are in hcp type of arrangement.

Zn²⁺ = 4

S^2- = 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

O^2- = 8

4