Suppression of Sequential Charge Transitions in Ca0.5Bi0.5FeO3 via B-Site Cobalt Substitution

The perovskite Ca0.5Bi0.5FeO3 containing unusually high-valent Fe3.5+ 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 Ca0.5Bi3+0.5(Fe1–xCox)3.5+O3 and destabilizes the CD state. This results in materials exhibiting only intermetallic charge transfer behavior in the region 0.01 < x < 0.67. The CT transitions for these materials only involve Fe3.5+, whereas Co remains in the 3.5+ oxidation state at all temperatures. The doped Co3.5+ ions give Pauli-paramagnetic like conducting behavior. The Co-substitution effect is very different from that observed in CaFe1–xCoxO3.