Origin of the intriguing physical properties in A-site-ordered LaCu3Fe4O12 double perovskite

Our density functional theory calculations show that the origin of the stability of the Cu3+ oxide, LaCu3Fe4O12, is the strong hybridization interaction between La-O-Cu, which also suppresses structural symmetry change with changing temperature. From low-temperature antiferromagnetism to high-temperature paramagnetism, each Fe ion loses 0.34 electron and each Cu ion gets 0.45 electron, while the charges of La and O ions do not change. Additionally, each type of ion has the same total charge. The Coulomb attractive force between Fe-O-Fe at high temperature is stronger than that at low temperature, driving a large negative thermal expansion.