Abstract
The formation and phase stability of the intermediate compounds and solid solutions in binary systems R2O3-other oxides (R=Rare earth) were reviewed and discussed from the ionic point of view: ionic scale parameter of field strength, lattice energy and site self-potentials in every sublattices.
The intermediate compounds and their phase relations were summarized in the series of systems R2O 3-WO3. Equilibrium phase diagrams for La2O3, Nd2O3 and Y2O3 were revised from previously reported ones.
In fluorite-related phases of R3TaO7, the smaller R ions led to the formation of the more disordered and higher symmetric phases.
The phase diagrams of the solid solutions in the systems ZrO2-CeO2, or-Y2O3, were also reviewed from the point of view of stable and metastable equilibria. The metastability seems to be caused by extremely slow diffusion of cation and fast diffusion of anion, and by martensitic phase transformation, in the fluorite-related phases.
The formation and stability of high-valence state of cations in the B-site of the perovskite lattice ABO3 were explained by the contribution of deep site self-potential at the B-site in this perovskite lattice.
