STRUCTURE OF ISOTHERMAL SECTIONS OF THE DIAGRAM OF THE STATE OF THE SYSTEM ZrO2 – La2O3 – Eu2O3 AT TEMPERATURES 1500 AND 1250 °C

Abstract

Using the methods of X-ray phase and microstructural analyzes, phase equilibria and structural transformations in the ZrO2 – La2O3 – Eu2O3 system at temperatures of 1500 and 1250 ºC in the whole range of concentrations were studied. Based on the obtained data, the corresponding isothermal cross sections are constructed. It is established that the fields of solid solutions are formed in the system on the basis of cubic (F) modification with fluorite type structure, tetragonal (T) modification ZrO2, monoclinic (B) and cubic (C) modifications Eu2O3, hexagonal (A) modification La2O3, as well as ordered phases with a structure of the pyrochlor type Ln2Zr2O7 (Py). The boundaries of the phase fields and the parameters of the unit cells of the formed phases are determined. It was found that in the region with a high content of ZrO2 solid solutions are formed on the basis of tetragonal modification of ZrO2. The solubility of La2O3 in T-ZrO2is small and is ∼ 0.5% (mol.), which is confirmed by X-ray phase analysis and microstructural studies. It is established that at 1500 and 1250°C a continuous series of solid solutions is formed on the basis of an ordered phase of pyrochlor (Py) type Ln2Zr2O7. With decreasing temperature, the region of homogeneity of the specified solid solution narrows. Isothermal cross sections of the state diagram of the ZrO2-La2O3-Eu2O3 system at 1500 and 1250°C have a similar structure, although they are characterized by some differences due to the structure of the limiting binary systems. No new phases in the ternary system ZrO2 – La2O3 – Eu2O3 were detected at the studied temperatures.