Non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by integers; most often, in such materials, some small percentage of atoms are missing or too many atoms are packed into an otherwise perfect lattice work. exaple FeO, ZnO etc.

Silver bromide (AgBr) has both Schottky and Frenkel defects together.

In body centred cubic crystal packing effciency is 68% thus free space in body centred cubic crystal is free space effciency = 100- 68%
                              = 32%

Antiferro electric solid-PbZrO₃ (Lead Zirconate).
Ferro electric solid-BaTiO₃ (Barium Titanate).