Studying local structural, valence, and magnetic states of iron ions in Bi0.9Ca0.1FeO3 perovskite

Mössbauer method was used to study a perovskite compound Bi_0.9Ca_0.1FeO₃ at T = 295 K and at temperature above T _N . It has been established that Bi_0.9Ca_0.1FeO₃ has a rhombohedral crystal structure similar to that of BiFeO₃. The substitution of Ca²⁺ for Bi³⁺ ions leads to the formation of three states of Fe³⁺ ions with an octahedral surroundings and one state with a tetrahedral oxygen surroundings with substantially different hyperfine magnetic fields. All Fe ions are in a trivalent state; the compensation of the charge deficit occurs via the formation of oxygen vacancies. Above T _N , two structurally nonequivalent states of Fe³⁺ ions exist in the Bi_0.9Ca_0.1FeO₃ sample, which correspond to the Fe³⁺ ions with an octahedral and tetrahedral oxygen coordination.