Controlled coordination and oxidation states of copper and manganese cations in complex nickel–copper–cobalt–manganese oxide thin films

Thin thermistor films of [formula omitted] [formula omitted] and 1.2) were prepared by the deposition of metalorganic solutions followed by furnace annealing at temperatures between 600 and 800 °C. Annealing temperatures are decisive factors to control the electrical properties and electronic structure. X-ray photoelectron spectroscopy revealed that the specimens contained a mixture of [formula omitted] and [formula omitted] cations, and the annealing caused the change of the oxidation state from [formula omitted] to [formula omitted] which was accompanied by the reduction of manganese cations from [formula omitted] to [formula omitted] The [formula omitted] core level from the [formula omitted] state along with [formula omitted] levels showed unusually large negative binding energy shifts [formula omitted] at 930.8 eV and [formula omitted] at 950.6 eV). Extended x-ray absorption fine structure showed that all manganese ions were located in octahedral sites of the spinel lattice, and both [formula omitted] and [formula omitted] cations occupy the tetrahedral sites regardless of the annealing temperature. X-ray absorption near edge structure spectra of the [formula omitted] edge confirmed the reduction of manganese at high temperature. [formula omitted]-edge spectra confirmed the presence of the cations with anomalous position in the [formula omitted] states, thus the negative shift of the [formula omitted] core was attributed to the tetrahedral coordination of these cations in the spinel structure.