Abstract
The cation valence and distribution in copper manganese spinels containing 1.0–1.6 mol copper per formula unit (Cu x Mn 3− x O 4) 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 Mn 4+ to Cu 2+ and Mn 3+ and the disproportionation of the Jahn–Teller ion Mn 3+ into Mn 2+ and Mn 4+. Thermodynamic parameters for the redox reaction were determined from experimental data as well as calculated, confirming the validity of the modeled defect equilibria.
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