Chapters / Chapter 1 · Solid state / Topic 9 of 14
Ionic crystals of AB type
Chapter 1 · Solid state and crystal structures
AB type, four structures
NaCl, CsCl, ZnS (zinc blende) and ZnS (wurtzite).
| Structure | Coordination | Anion array | Cation site |
|---|---|---|---|
| NaCl (rock salt) | 6:6 | fcc Cl− | Na+ in all octahedral holes; 4 Na+ and 4 Cl− per cell |
| CsCl | 8:8 | Simple cubic Cl− | Cs+ at the body centre; 1 of each per cell |
| ZnS, zinc blende | 4:4 | fcc S2− | Zn2+ in half the tetrahedral holes; 4 of each per cell |
| ZnS, wurtzite | 4:4 | hcp S2− | Zn2+ in half the tetrahedral holes |
Zinc blende and wurtzite have the same 4:4 coordination and the same stoichiometry; they differ in the stacking of the anion array, ccp in zinc blende, hcp in wurtzite.