Sequential Phase Transitions in Sm Substituted BiFeO₃

Abstract

The compositional and thermal evolution of the crystal structure of the Bi_1-xSm_xFeO₃ solid solution synthesized under a high pressure was investigated. Samples with 0.10≤×≤0.20 had an antipolar PbZrO₃-type structure with a √2a×2√2a×4a perovskite superstructure at room temperature, while the sample with x=0.05 had a rhombohedral BiFeO₃-type structure. Among them, the samples with 0.10≤x≤0.12 transformed from an antipolar PbZrO₃-type structure to a polar BiFeO₃-type structure and finally to a nonpolar GdFeO₃-type structure on heating, which is similar to Zr-rich Pb(Zr,Ti)O₃. On the other hand, the samples with 0.15≤x≤0.20 transformed directly to a nonpolar GdFeO₃-type structure. The ferroelectric Curie temperature of BiFeO3 was markedly lowered by the Sm substitution.