CATION VALENCIES AND DISTRIBUTION IN THE SPINELS NIMN2O4 AND MZNIMN2-ZO4 (M = LI, CU) STUDIED BY XPS

Photoelectron spectroscopic investigations (XPS) of the spinels NiMn2O4 and MzNiMn2-zO4 (M = Li, Cu) in comparison with Mn2TiO4, ZnMn2O4, and MgNiMnO4, containing Mn in only one oxidation state, show that in the former compounds Mn(II), Mn(III), and Mn(IV) are present. By a fitting process yielding the amounts of the Mn ions in the different oxidation states it is possible to determine the cation distribution of NiMn2O4 which is characterized by a high inversion parameter and a considerable degree of disproportionation. Cation valencies and their distribution in the substituted spinels are discussed. An increasing concentration of Mn(IV) with higher values of z is reflected in the spectra by shift of the Mn p signals and by changes in their shape.