The preparation, characterization and electrical properties of copper manganite spinels, Cu_xMn_3−xO₄, 0 ⩽x ⩽ 1

Abstract

Single-phase copper manganite spinels Cu _x Mn_3−x O₄ with 0⩽x⩽1 were prepared by a careful thermal processing of copper-manganese co-precipitated hydroxide precursors. Powder X-ray diffraction (XRD) analysis of these spinels revealed the presence of a tetragonally distorted single spinel phase, with tetragonal distortionc/a > 1 which decreases with copper content. Thermogravimetric analysis (TGA) curves, run in an oxygen atmosphere for all the compositions studied, are characterized by a stability step up to 250 to 300° C, followed by a domain of oxidation between 300 and 900° C and finally a domain of reduction that restores the initial stoichiometry of the samples. The oxidation is observed to occur in two successive steps. The phenomenon appearing at the low temperature is due to the oxidation of Cu⁺ ions, while that at higher temperature corresponds to the oxidation of Mn²⁺ ions in tetrahedral sites. Further, electrical resistivity measurements confirm the presence of Cu⁺ ions on the tetrahedral sublattice of spinel. Correlation of the results obtained by XRD, TGA and electrical resistivity measurements permits one to infer the cation distribution, given by Cu ⁺_x Mn ²⁺_1−x [Mn ³⁺_2−x Mn ⁴⁺_x ] O ²⁻₄ .