Charge Disproportionation and Charge Transfer in A-site Ordered Perovskites Containing Iron

New A-site ordered perovskite structure oxides, CaCu3Fe4O12 and LaCu3Fe4O12, were synthesized under high-pressure and high-temperature conditions. The compounds contain unusually high valence states of iron: Fe4+ in CaCu3Fe4O12 and Fe3.75+ in LaCu3Fe4O12, Instabilities of the high oxidation states at low temperatures are resolved in CaCu3Fe4O12 by charge disproportionation from Fe4+ to Fe3+ and Fe5+ and in LaCu3Fe4O12 by charge transfer between A-site copper and B-site iron ions. The charge disproportionation and the charge transfer are accompanied by significant changes in structural, transport, and magnetic properties.