Phase equilibria in a portion of the system La2O3-BaO-P2O5 rich in P2O5

This paper appears in the sequence of our investigation of the ternary system La2O3-BaO-P2O5 and it concerns the phase diagram of the partial system LaPO4Ba(PO3)(2)-LaP5O14 Phase equilibria in this partial system were not known, so far. Known are only the phase diagrams of the three side-systems LaPO4-P2O5 [1,2], Ba(PO3)(2)-P2O5 [3] and LaPO4-Ba(PO3)(2) [4]. According to [1], in tbe system LaPO4-P2O5 three intermediate compounds occur: La2P4O13, La(PO3)(3) and LaP5O14. The compound La2P4O13 exists only in the solid phase up to 755 degrees C. The existence of the phosphate La2P4O13 was not confirmed [2]. The metaphosphate La(PO3)(3) melts incongruently at 1235 degrees C to give LaPO4 and a liquid. The ultraphosphate LaP5O14 melts congruently at 1095 degrees C and it is thermally unstable. In the side-system LaPO4-Ba(PO3)(2) an eutectic occurs at a composition of 96 wt% of Ba(PO3)(2) and 4 wt% of LaPO4 at 825 degrees C.