On the stabilities of the lower oxides of the rare earths

Abstract

The stabilities of the lower oxides of samarium, europium and ytterbium are discussed. An extensive review of the methods of preparing the lower oxides and their degree of success is presented. Thermodynamic calculations are performed which indicate the great stability of EuO. SmO and YbO are not stable phases at high temperatures and all high-temperature attempts to prepare them have failed. Thermodynamic considerations indicate that YbO may be stable at low temperatures and recent results indicate that it may be able to be prepared under such conditions. Crystal chemical stabilization offers the greatest hope of preparing Yb 2+ and Sm 2+ in oxides. Recent thermodynamic data on the europium oxides are utilized to calculate stability among these oxides as a function of fo 2 and T. Based on these calculations and recent literature, a not-impossible T—X phase diagram for EuEu 2O 3 is constructed. Suggestions for further work are given throughout.