Phase equilibrium in binary La2O3-Dy2O3 and ternary CeO2-La2O3-Dy2O3 systems.

Cerium oxide doped with oxides of rare earth elements is a multifunctional material, a wide range of uses which is associated with its unique physicochemical properties. Phase diagrams of multicomponent systems are the physicochemical basis for the creation of new materials with improved characteristics. In this work, phase equilibria in ternary CeO 2 –La 2 O 3 –Dy 2 O 3 and binary La 2 O 3 –Dy 2 O 3 systems in the whole concentration range were studied. No new phases have been identified in these systems. An isothermal section of the phase diagram of the CeO 2 –La 2 O 3 –Dy 2 O 3 system at a temperature of 1500 °С is constructed. No new phases have been detected in the system. It was found that in the studied ternary system solid solutions are formed on the basis of (F) modification of CeO 2 with structure of fluorite type, monoclinic (B), cubic (C) and hexagonal (A) modifications of Ln 2 O 3. In the La 2 O 3 –Dy 2 O 3 binary system (1500–1100 °С) three types of solid solutions are formed: based on hexagonal modification A-La 2 O 3 , monoclinic modification B-Dy 2 O 3 and cubic modification C-Dy 2 O 3 separated by two-phase fields (A+B) and (B+C), respectively. The boundaries of the regions of homogeneity of solid solutions based on A-La 2 O 3 are determined by compositions containing 35–40, 20–25, 15–20 mol% Dy 2 O 3 at 1500, 1250, 1100 °C, respectively. From the obtained data it follows that the solubility of Dy 2 O 3 in the hexagonal modification of lanthanum oxide is 39 mol% at 1500 °C, 23 mol. % at 1250 °C and 16 mol% at 1100 °C. The limits of existence of solid solutions based on monoclinic B-modification are determined by compositions containing 30–35, 65–60 (1250 °С), 35–40, 55–60 (1100 °С) 40–45, 70–75 (1500 °C) mol% Dy 2 O 3. In the studied system, with a decrease in temperature from 1500° to 1100°C, there is a decrease in the solubility of La 2 O 3 in the crystal lattice of cubic solid solutions of C-type from 16 to 10 mol%. [ABSTRACT FROM AUTHOR]