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

Abstract

The perovskite Ca_0.5Bi_0.5FeO₃ containing unusually high-valent Fe^3.5+ undergoes sequentially charge disproportionation (CD) of the Fe centers and intersite charge transfer (CT) between Bi and Fe. From structural, magnetic, and transport property characterization, we found that substitution of Co for Fe occurs isovalently to form Ca_0.5­Bi³⁺_0.5­(Fe_1–<i>x</i>­Co_<i>x</i>)^3.5+­O₃ and destabilizes the CD state. This results in materials exhibiting only intermetallic charge transfer behavior in the region 0.01 < <i>x</i> < 0.67. The CT transitions for these materials only involve 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-substitution effect is very different from that observed in Ca­Fe_1–<i>x</i>­Co_<i>x</i>O₃