Solid State Reactions Involving Oxides of Trivalent Cations

Selected mixtures in 69 binary systems involving Al₂O₃, Ga₂O₃, Cr₂O₃, Fe₂O₃, Sc₂O₃, In₂O₃, Y₂O₃, and the rare earth oxides were studied by X-ray diffraction techniques after heat treatment at various temperatures. A plot of the radii of the A⁺³ cations versus the radii of B⁺³ cations shows the regions of stability for the different structure types found for the double oxides of the trivalent cations. The following structure types were encountered: A, B, and C-type rare earth oxide; corundum, beta gallia; kappa alumina; garnet; perovskite; and several types which could not be definitely related to known structures. The majority of A⁺³B⁺³O₃ compounds have the perovskite structure. Several phases, including (1-x)Fe₂O₃·xAl₂O_{3 ss} and (1-x)Fe₂O₃·Ga₂O_{3 ss}, appear to have structures similar to kappa alumina. Solid solution definitely occurs in many of the garnet type compounds which contain gallia. Based on the data collected in this survey, the subsolidus phase equilibria relationships of 79 binary systems were drawn.