Phase equilibria in the La2O3-Y2O3-Gd2O3 system at 1500°C

Abstract

The phase equilibria in the ternary La2O3-Y2O3-Gd2O3 system at 1500?C were studied by X-ray diffraction, petrography and electron microscopy in the overall concentration range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying and calcination at 1100 and 1500?C. The solid solutions based on various polymorphous forms of constituent phases and ordered phase of LaYO3 were revealed in the system. The isothermal section of the phase diagram for the La2O3-Y2O3-Gd2O3 system has been developed. It was established that in the ternary La2O3-Y2O3-Gd2O3 system fields of solid solutions exist based on hexagonal (A) La2O3 phase, monoclinic (B) modifications of La2O3 and Gd2O3, cubic (C) modification of Y2O3, as well as perovskite-type structure of LaYO3 (R) with rhombic distortions. The systematic study that covered the whole compositional range excluded the formation of new phases. The refined lattice parameters of the unit cell and the boundaries of the homogeneity fields for solid solutions were determined.