Electrical properties of copper–manganese spinel solutions and their cation valence and cation distribution Original Research Article

The cation valence and distribution in copper manganese spinels containing 1.0–1.6 mol copper per formula unit (CuxMn3−xO4) was resolved from their electrical conductivity and thermoelectric properties. The limit of thermal stability of the cubic spinel phase was also determined for each stoichiometry. A corrected phase diagram for the Cu–Mn–O system in air is proposed accordingly. The electronic defect structure could be described through a chemical approach, involving the competition between the redox of Cu+ and Mn4+ to Cu2+ and Mn3+ and the disproportionation of the Jahn–Teller ion Mn3+ into Mn2+ and Mn4+. Thermodynamic parameters for the redox reaction were determined from experimental data as well as calculated, confirming the validity of the modeled defect equilibria.