Eulytite-type solid solution in the LaPO4 – Ba3(PO4)2 system

Abstract Studies of phase equilibria in the LaPO4–Ba3(PO4)2 system were carried out in the whole concentration range in temperature scope up to 1950 °C using TGA/DSC, XRD and reflected light microscopy. Analysis of the results allowed to determine the phase relationships in the system. In the LaPO4–Ba3(PO4)2 system, there is an intermediate compound Ba3La(PO4)3 that divides the studied concentration range into two partial systems: LaPO4–Ba3La(PO4)3 and Ba3La(PO4)3–Ba3(PO4)2. They both have a eutectic character. Ba3La(PO4)3 is a thermodynamically stable phosphate at room temperature. At high temperature it forms a limited solid solution with Ba3(PO4)2. At 1450 °C, the maximum solubility of Ba3(PO4)2 in Ba3La(PO4)3 corresponds to phase of the Ba3.66La0.34(PO4)2.78 composition.