Structural and electronic properties of NiMn2O4

A theoretical study, based on computer simulation techniques, of the spinel-structured oxide, NiMn2O4, is presented. The precise nature of the cation distribution and valencies in NiMn2O4 is uncertain and is of importance in interpreting the electrical properties of this material. An examination of the relative energetics of the normal and inverse structures of NiMn2O4 and other manganese and nickel spinels is carried out. The simulations are successful in predicting the observed structures, when our potential model is modified to include the effects of change in cation coordination. We proceed with an investigation of the possible valence states in NiMn2O4 by examining several important electronic processes. Our results suggest that the observed semiconducting behaviour is due to hopping of charge-carriers between Mn2+ and Mn3+ ions at octahedral sites.