Glass formation and polyamorphism in rare-earth oxide-aluminum oxide compositions

We report formation of single- and two phase glasses from rare-earth oxide-alumina materials. Liquids with the Y(3)AI(5)O(12) and Er(3)AI(5)O(12) compositions underwent a liquid-liquid phase transition which resulted in glasses with a cloudy appearance due to spheroids of one glass in a matrix of a second glass. The two glasses were isocompositional within the limits of experimental error, Clear, brilliant, single-phase glasses were obtained from La(3)AI(5)O(12), ErLaYAI(5)O(12), and compositions containing greater than or equal to 5 mol% La2O3 substituted for the other rare-earth oxides. Formation of two glasses is attributed to nucleation and growth of the second liquid at a temperature below the equilibrium liquid-liquid transition temperature. Addition of lanthanum depresses the phase transition temperature below the glass transition temperature and the liquid-liquid phase transition is not observed. The results are discussed in the context of first-order liquid-liquid please transitions (polyamorphism) and formation of single-phase glass from liquids that contain a high proportion of 4-coordinate aluminum ions.