Phase equilibria in the oxide system Nd2O3–K2O–P2O5

A phase equilibria diagram of the partial system NdPO4–K3PO4–KPO3 has been developed as part of the research aimed at determining the phase equilibrium relationships in the oxide system Nd2O3–K2O–P2O5. The investigations were conducted using thermoanalytical techniques, X-ray powder diffraction analysis and reflected-light microscopy. Three isopleths existing between: K3Nd(PO4)2–K4P2O7, NdPO4–K5P3O10 and NdPO4–K4P2O7 have been identified in the partial NdPO4–K3PO4–KPO3 system. Previously unknown potassium-neodymium phosphate “K4Nd2P4O15” has been discovered in the latter isopleth section. This phosphate exists in the solid phase up to a temperature of 890 °C at which it decomposes into the parent phosphates NdPO4 and K4P2O7. Four invariant points: two quasi-ternary eutectics, E1 (1057 °C) and E2 (580 °C) and two quasi-ternary peritectics, P1 (1078 °C) and P2 (610 °C), occur in the NdPO4–K3PO4–KPO3 region.

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