Phase diagram for the system Nd-Mn-O and thermodynamic properties of NdMnO₃ and NdMn₂O₅

Abstract

Studies on the phase relations in the system Nd-Mn-O at 1223 K showed two stable ternary compounds, NdMnO₃ and NdMn₂O₅. An isothermal section of the ternary phase diagram for the system Nd-Mn-O was constructed based on phase analysis of samples quenched after equilibration using XRPD and EDS. An advanced version of the solid-state cell incorporating a buffer electrode was used to determine the Gibbs energies of decomposition of NdMnO₃ and NdMn₂O₅ in the temperature range from 925 to 1400 K. Pure oxygen gas at 0.1 MPa was used as the reference electrode, and yttria-stabilized zirconia as the solid electrolyte. The buffer electrode was designed to prevent polarization of the three-phase electrode and ensure accurate data. The measured oxygen potential corresponding to the reaction, 2Nd₂O₃+4MnO+O₂→4NdMnO₃ can be represented by the equation, Aμo₂/J.mol^-1 (±580)=-523 960+170.96(T/K) Similarly, for the formation of NdMn₂O₅ according to the reaction, 3NdMnO₃+Mn₃O₄+O₂→3NdMn₂O₅ Aμo₂/J.mol^-1 (±660)=-269 390+181.174 (T/K).