Suppression of Sequential Charge Transitions in Ca_0.5Bi_0.5FeO₃ via B-Site Cobalt Substitution

Abstract

The perovskite Ca0.5Bi0.5FeO3 containing unusually high valent Fe 3.5+ undergoes sequentially charge disproportionation (CD) of the Fe centres and intersite charge transfer (CT) between Bi and Fe. From structural, magnetic, and transport property characterization, we found that substitution of Fe with Co occurs isoelectronically to form Ca 0.5 Bi 0.5 3+ (Fe 1−x Co x) 3.5+ O 3 and destabilizes the CD state. This results in materials exhibiting only intermetallic charge transfer behaviour in the region 0.01 < x < 0.67. The CT transitions for these materials only involves Fe 3.5+ whereas Co remains in the 3.5+ oxidation state at all temperatures. The doped Co 3.5+ ions give Pauli-paramagnetic like conducting behavior. The Co-doping effect is very different from that observed in CaFe 1−x Co x O 3. The charge transition behavior of Fe 3.5+ in the present system are also in contrast to those in Ca0.5Bi0.5FeO3 and Sr0.5Bi0.5FeO3.