1.7.3 Zinc Blende (MX) Structure

• MX type compounds, also called as sphalerite structured compounds based on a mineral name of sphalerite.

• Mostly oxides and sulphides follow this structure. Examples are  ZnO, ZnS, BeO etc.

• Some covalently bonded materials and compounds have similar structure such as GaAs, SiC, BN. You can also visualize diamond also having similar structure with both anion and cation being of same type.

• Typically compounds with tetrahedral co-ordination assume this structure.

• In this structure anions form FCC lattice and cations occupy the tetrahedral interstices.

• Due to stoichiometry, half of the tetrahedral sites are filled.

• Compounds with radius ratio  : 0.225-0.414 follow this structure with a few exceptions where bonding favours a tetrahedral coordination despite unfavourable radius ratio, especially covalently bonded compounds.

• Examples:Zn²⁺ - 0.06 nm,Be²⁺ - 0.027 nm,O^2- - 0.14 nm, S^2-- 0.184 nm




Figure 1.29 Zinc Blende or Sphalerite structure

• Coordination numbers: M - 4, X - 4

• Lattice type: FCC

• Motif: M – 0 0 0; X – ¼ ¼ ¼

• 4 formula units per unit cell.

• Tetrahedra are shared at corners.