Phase Equilibria in Systems Involving the Rare - Earth Oxides . Part II . Solid State Reactions in Trivalent Rare - Earth Oxide Systems

Selected mixtures in 2 l binary and 9 ternary rare-earth oxide syste ms were studied by X-ray diffraction after heat treatment aL 1,650° C and above. Two graphs were drawn to show specific r egions of stability for t he various strucLure types. Each givcs t he a verage ionic rad ius of constiLuent cations versus the mole percent of the smaller cation. One diagram is es~e ntiall :-' divided inLo areas of solid solution of t he A, B, and C rare-eart h oxide struct ure types. The other indicaLes a field of perovskite-type compou nds bordered by regions of A, B , or C so lid soluLions. These diagrams were used to predict Lhe subsolidus phase diagrams of a number of syste ms. A total of forty-one subsolidu s binar y and one temar.v rare-earth oxide sy Lems were given. A tolerance fac tor equal to 0.77 was assigned as the minimum value for the form aLion of a perovskite-type compound.