Energetics and structure of the B‐type solid solution in the Nd2O3–Y2O3 system

Abstract The system Nd 2 O 3 –Y 2 O 3 contains solid‐solution phases with several different structures. Single‐phase B‐type (Nd 1− x Y x ) 2 O 3 solid solutions in the range of were formed at 1873 K and retained on cooling to ambient temperature. They showed a linear composition dependence of lattice parameters, enabling extrapolation to x = 0 and 1 for comparison with the structures of the stable endmembers. A positive enthalpy of formation from A‐type Nd 2 O 3 and C‐type Y 2 O 3 determined using oxide melt solution calorimetry indicated entropic stabilization of the B‐type phase. A positive interaction parameter for mixing in the B‐type solid solution, Ω 47.46 ± 4.04 kJ/mol, was obtained by fitting the data using a regular solution model. This value is significantly more positive than that obtained by previous phase diagram analysis using the CalPhaD approach. Exsolution into two B‐type phases is predicted to occur below 1427 K, making it unimportant for the equilibrium phase relations that will be dominated by other structures at low temperature.