Phase diagrams and thermodynamic properties of unary and binary rare-earth sesquioxide (RE2O3) systems (RE = all lanthanides, Y, and Sc)

Abstract

All phase diagram and thermodynamic property data of unary rare-earth sesquioxides (RE₂O₃) in literature have been critically evaluated to obtain a consistent set of thermodynamic data for all six stable and metastable phases (C, B, A, H, X, and L) of RE₂O₃. In the evaluation, systematic energetic trends of RE₂O₃ depending on ionic radius of RE and the extrapolated data from RE₂O₃ containing binary systems were taken into account to obtain more accurate thermodynamic property data and phase transition data. Based on the newly established Gibbs energies of unary RE₂O₃ phases, the CALPHAD-type thermodynamic modeling was carried out for inter RE₂O₃ binary systems to obtain the thermodynamic models with optimized model parameters of all solid and liquid solutions, which can successfully reproduce all available and reliable experimental phase diagram data of the binary RE₂O₃–RE′₂O₃ systems. Using thermodynamic models with established model parameters, a complete phase diagram set of all 136 binary RE₂O₃–RE′₂O₃ systems were predicted for the first time. The models with established parameters can be readily expanded to any ternary and high order rare oxide systems for the phase diagram and thermodynamic property calculations.