New Solid Solutions and Phase Equilibria in the Rb3Y(PO4)2–BaRbPO4 System

Abstract

A phase diagram of the Rb3Y(PO4)2–BaRbPO4 system for the whole range of compositions, up to a temperature of 1700°C, has been developed on the basis of the results of thermal and XRD analyses and microscopic examinations. The investigated system has an eutectic character. Limited solid solutions with the high‐temperature (α) and low‐temperature (β) structure of BaRbPO4 form in this system. The maximum solubility of Rb3Y(PO4)2 in the high‐temperature solid solution (αss) occurs at the eutectic temperature (1275°C), amounting to ~80 mass% Rb3Y(PO4)2. At 988°C, the αss decomposes according to eutectoidal reaction: αss ↔ βs + Rb3Y(PO4)2. The maximum content of Rb3Y(PO4)2 in the low‐temperature limited solid solution (βss) does not exceed 10 mass% Rb3Y(PO4)2. The αss phase has a hexagonal glaserite‐like structure with the unit cell parameters a ≈ 5.7 and b ≈ 8.1 Å.