Thermochemistry of binary rare earth oxides

Abstract

7.7. Conclusions: In this chapter we have shown that the thermochemistry of the rare-earth oxides is well established for the majority of the stoichiometric compounds. The thermodynamic properties follow clear trends that can be understood in terms of valence states and electronic configurations of the lanthanide ions and metals. For the sesquioxides, the principal group of rare earth compounds, the data are reliable up to 2000 K, an interval in which the A, B and C phases are stable. However, for the high-temperatures, where the H and X phases are stable, no experimental data exist. Enthalpies of formation remain to be measured for some of the lanthanide sesquioxides, e.g. La 2O3(bcc), Nd2O3(monoclinic) and Gd2O3(monoclinic). The enthalpy of formation of Ce 2O3 remains in doubt because of the discrepancy between solution and combustion calorimetry values (section 4.1). The thermochemical properties of metallic monoxides should be measured, but only when stoichiometric samples that are free of unreacted metal can be synthesized. An area that needs further systematic study is the thermochemistry of gaseous oxides. Utilization of REMPI, MATI, and theoretical computations should lead to a systematic understanding of excitation energies and intrinsic bond energies that will enable better predictions to be made of corresponding trends for the actinide monoxides. © 2005 Springer Science + Business Media, Inc.