2018 Volume 65 Issue 5 Pages 269-273
Sr0.5−xCaxBi0.5FeO3 (0.0 ≤ x ≤ 0.5) perovskite compounds, which are solid solutions between Sr0.5Bi0.5FeO3 (x = 0.0) that shows a single charge disproportionation (CD) transition and Ca0.5Bi0.5FeO3 (x = 0.5) that shows successive CD and intermetallic-charge-transfer (CT) transitions, were obtained by high pressure syntheses. The crystal structure at room temperature changes from rhombohedral (0.0 ≤ x ≤ 0.1) to orthorhombic (0.2 ≤ x ≤ 0.5). Unusual-high-valence Fe3.5+ ion is stabilized in the entire range of the solid solution at room temperature, and undergoes a charge transition to relieve the electronic instability. Fe3.5+ in the range 0.0 ≤ x ≤ 0.4 shows a single 3:1 CD transition (Fe3.5+ → 3/4Fe3+ + 1/4Fe5+), and Bi3+ ion does not act as counter cations accepting charges as in Ca0.5Bi0.5FeO3. The difference in the crystal structure symmetry does not influence the 3:1 CD transition, and the transition temperature decreases monotonously with increasing x in the region 0.0 ≤ x ≤ 0.4.