Os Doping Suppressed Cu-Fe Charge Transfer and Induced Structural and Magnetic Phase Transitions in LaCuFeOsO ( = 1 and 2).

B-site Os-doped quadruple perovskite oxides LaCuFeOsO ( = 1 and 2) were prepared under high-pressure and high-temperature conditions. Although parent compound LaCuFeO experiences Cu-Fe intermetallic charge transfer that changes the Cu/Fe charge combination to Cu/Fe at 393 K, in the Os-doped samples, the Cu and Fe charge states are found to be constant 2+ and 3+, respectively, indicating the complete suppression of charge transfer. Correspondingly, Os and mixed Os valence states are determined by X-ray absorption spectroscopy for = 1 and = 2 compositions, respectively. The = 1 sample crystallizes in an Fe/Os disordered structure with the 3̅ space group. It experiences a spin-glass transition around 480 K. With further Os substitution up to = 2, the crystal symmetry changes to 3̅, where Fe and Os are orderly distributed in a rocksalt-type fashion at the B site. Moreover, this composition shows a long-range Cu(↑)Fe(↑)Os(↓) ferrimagnetic ordering near 520 K. This work provides a rare example for 5d substitution-suppressed intermetallic charge transfer as well as induced structural and magnetic phase transitions with high spin ordering temperature.