Thermal Dissociation of RMnO₃ (R = Dy, Yb, Lu)

Abstract

The phase equilibria involved in the thermal dissociation of RMnO₃ (R = Dy, Yb, Lu) were studied in the range 973–1173 K by a static method in a vacuum circulation unit and by x-ray diffraction analysis of quenched solid phases. The RMnO₃ manganites were shown to dissociate by the reaction RMnO₃ = 1/2R₂O₃ + MnO + 1/4O₂. The temperature dependences of the equilibrium oxygen pressure and Gibbs energy change in this reaction were determined for the three compounds. The experimental data were used to evaluate the standard thermodynamic functions of formation of RMnO₃ from R₂O₃ and Mn₂O₃: ΔH ⁰(T) = −88.93 kJ/mol, Δ S ⁰(T) = 46.56 J/(mol K) for DyMnO₃; ΔH ⁰(T) = −130.95 kJ/mol, Δ S ⁰(T) = 86.25 J/(mol K) for YbMnO₃; ΔH ⁰(T) = −142.94 kJ/mol, Δ S ⁰(T) = 102.87 J/(mol K) for LuMnO₃.