Thermodynamic and Structural Properties of CuCrO₂ and CuCr₂O₄: Experimental Investigation and Phase Equilibria Modeling of the Cu–Cr–O System

Abstract

This work considers the equilibria between the stable phases of the Cr–Cu–O ternary chemical system at atmospheric pressure and in a large temperature range that includes the high-temperature liquid phase. Based on a thorough evaluation of literature data, we performed complementary experimental investigations of solid-phase properties (especially the mixed oxides) by implementation of spark plasma sintering and microanalysis, high-temperature X-ray diffraction combined with Rietveld analysis, differential thermal analysis, and thermogravimetry. We show that neither the spinel CuCr2O4 nor the delafossite CuCrO2 phases exhibit significant cationic nonstoichiometry. We provide an assessment of the thermodynamic functions of the spinel up to 1200 K, taking into account the α/β phase transition. We propose, for the first time, a consistent thermodynamic description of the Cr–Cu–O system based on the Calphad method, allowing the computation of reactions and phase equilibria, including the high-temperature liquid phase described by the modified quasichemical model.