1 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;2 School of Physics, University of Chinese Academy of Sciences, Beijing 100049, China;3 Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201203, China;4 "National" Synchrotron Radiation Research Center, 101 Hsin-Ann Road, Hsinchu 30076, Taiwan, China;5 Institute for Brain Research and Rehabilitation, South China Normal University, Guangzhou 510631, China;6 Department of Physics and Synergetic Innovation Center for Quantum Effects and Applications of Hunan, Hunan Normal University, Changsha 410081, China>
A new oxide CaCr0.5Fe0.5O3 was prepared under high pressure and temperature conditions. It crystallizes in a B-site disordered Pbnm perovskite structure. The charge combination is determined to be Cr5+/Fe3+ with the presence of unusual Cr5+ state in octahedral coordination, although Cr4+ and Fe4+ occur in the related perovskites CaCrO3 and CaFeO3. The randomly distributed Cr5+ and Fe3+ spins lead to short-range ferromagnetic coupling, whereas an antiferromagnetic phase transition takes place near 50 K due to the Fe3+-O-Fe3+ interaction. In spite of the B-site Cr5+/Fe3+ disorder, the compound exhibits electrical insulating behavior. First-principles calculations further demonstrate the formation of CaCr0.55+Fe0.53+O3 charge combination, and the electron correlation effect of Fe3+ plays an important role for the insulting ground state. CaCr0.5Fe0.5O3 provides the first Cr5+ perovskite system with octahedral coordination, opening a new avenue to explore novel transition-metal oxides with exotic charge states.
Project supported by the National Natural Science Foundation of China (Grant Nos. 11574378, 51772324, and 61404052), the National Basic Research Program of China (Grant No. 2014CB921500), and the Chinese Academy of Sciences (Grant Nos. YZ201555, QYZDB-SSW-SLH013, GJHZ1773, and XDB07030300).