Answer For each of the possible cation pairings we need to consider whether the sizes of the ions permit
the occurrence of the two structures. Starting with Zn 2+ and Ti 4+ we can predict that ZnTiO 3 does not exist
as a perovskite as the Zn 2+ ion is too small for the A-type site with B as Ti 4+ ; likewise, PbIn 2 O 4 does not
adopt the spinel structure as the Pb 2+ cation is too large for the tetrahedral sites. We conclude that the
permitted structures are PbTiO 3 (perovskite), TiZn 2 O 4 (spinel), and ZnIn 2 O 4 (spinel).