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

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)