Reinvestigation of the Phase Equilibria in the La2O3-P2O5 System

The phase equilibria between the solid phases in the La2O3-P2O5 system were reinvestigated with solid state reaction method. The existence of La3PO7, La7P3O18, LaPO4, and LaP3O9 was confirmed. La7P3O18 can form only at similar to 1200 A degrees C or higher possibly due to kinetic reasons, but it is stable at lower temperatures. On the other hand, three intermediate compounds proposed to exist, La5PO10, La-4(P2O7)(3), and La2P4O13 were not obtained in this study. Based on the literature, La-4(P2O7)(3) and La2P4O13 are considered to be metastable phases, although thermodynamic evidence is still required.