Phase equilibria in the system Nd2O3|P2O5|H2O was studied under a hydrothermal condition at 500°C under 100 MPa by a quenching technique using encapsuled samples. Equilibria among Nd phosphates; NdP5O14, NdP3O9 and NdPO4, and liquid phase could be attained within 24 h. The stability fields for liquid (L), NdP5O14+L, NdP5O14+NdP3O9+L, NdP3O9+L, NdP3O9+NdPO4+L, NdPO4+L and NdPO4+Nd(OH)3+H2O have been determined. The composition of the liquid phase with which NdP5O14 and NdP3O9 or NdP3O9 and NdPO4 could coexist was 3% Nd2O3-80% P2O5-17% H2O or 4% Nd2O3-73% P2O5-23% H2O respectively, at 500°C under 100 MPa. A phase diagram was constructed under this condition. Crystal growth of NdP5O14 were tried under the equilibrium condition. Diamond-shaped crystals 0.3 mm in size were grown at 500°C for 4 days under 100 MPa. Crystals tended to show aggregation and surface roughness at lower growth temperatures. The crystals with polyhedral shape and maximum 0.5 mm in size were grown at 650°C.
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