Cation valencies and distribution in the spinels CoxCuyMnzFeuO4+δ (δ≥0) thin films studied by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) has been used to elucidate the valencies and cation distribution of the copper and manganese in the spinels CoxCuyMnzFeuO4+delta (delta greater than or equal to 0) as thin films prepared by r.f. sputtering on glass substrates. The results obtained show that identification of the two Cu (Cu+ and CU2+) and three Mn (Mn2+, Mn3+, Mn4+) species in the stoichiometric (delta = 0) thin film is possible using XPS in the Cu2p(3/2) region and in the Mn2p(3/2), Mn3p and Mn3s regions. By a fitting process yielding the amounts of the Cu and Mn ions in the different oxidation states it is possible to determine the cation distribution among the two sublattices of the spinel structure. Significant changes were noted when the thin film was oxidized in cation deficient spinel. These changes included the total oxidation of Cu+ and Mn2+ ions with a variation in the relative amounts of Mn3+ and Mn4+ ions in the oxide film. A good agreement was obtained with the cation distribution established by thermogravimetry of the oxidation of thick films. (C) 1999 Elsevier Science S.A. All rights reserved.