Crystal Chemistry of Some AB ₂ O ₄ Compounds

Abstract

Compounds having the formulas BaGa 2 O 4 , BaCr 2 O 4 , BaFe 2 O 4 , PbAL 2 O 4 , PbGa 2 O 4 , PbCr 2 O 4 , SrAl 2 O 4 , SrGa 2 O 4 , and SrCr 2 O 4 were synthesized by heating oxide or carbonate mixtures. All were examined by X‐ray powder techniques. Single crystals of BaCr 2 O 4 , SrAl 2 O 4 , SrGa 2 O 4 , and BaGa 2 O 4 were also examined. SrAl 2 O 4 , SrGa 2 O 4 , and BaGa 2 O 4 are structurally similar to BaAl 2 O 4 and are thus related to tridymite (SO 2 ). The occurrence of these stuffed tridymite structures, as well as the other principal structures encountered (spinel, CaFe 2 O 4 , and perovskite types) can be correlated with the ionic radii of the cations. New special structures peculiar to one compound, e.g., α ‐CaCr 2 O 4 , occur at radius ratio values representing a transition between two principal structure types.