Phase relations in the K3Ln(PO4)2-K3Ln(VO4)2 (Ln = La, Gd) systems

Phase relations in the K(3)Ln(PO4)(2)-K(3)Ln(VO4)(2) (Ln = La, Gd) systems at 770 degrees C were studied by x-ray diffraction analysis. Single-phase K(3)Ln(PO4)(x)(VO4)(2-x) (X = 0-2.0) materials were prepared by solid-state reactions between Ln(2)O(3), K2CO3, KH2PO4, and NH4VO3 in the course of steplike heating from 70 to 770 degrees C. Both systems were shown to contain a continuous series of solid solutions with the arcanite structure. The unit-cell parameters and volume of the solid solutions were determined. The materials were found to pick up water vapor and CO2 in amounts dependent on their composition.