Oxidation mechanism and valence states of copper and manganese in tetragonal CuMn2O4

Abstract

With the view of determining the ionic configuration in tetragonal CuMn₂O₄ spinels prepared between 850 and 930 °C, the valence states of copper and manganese and the oxidation mechanism of these compounds have been determined by XPS, FTIR spectroscopy analyses and DTG measurements. For unoxidized samples, XPS spectroscopy analysis shows a predominately monovalent copper located in tetrahedral sites. Divalent copper in octahedral sites is also present, but at a lower level. Similar results are obtained for oxidized samples. FTIR data, upon oxidation of Cu and Mn ions below 500 °C, confirm the formation of a metastable spinel phase Cu_1.5Mn_1.5O₄ with a 1:3 ordering on the octahedral sublattice. A quantitative analysis by DTG mainly based on the difference of reactivity of Cu and Mn ions allows measurement of the content of each cation and determination of the ionic configuration.