Phase diagram of the system Al2O3-Nd2O3 at high temperatures.

The liquidus temperature of the Al2O3-Nd2O3 system was measured from the cooling curve of specimens by the specular reflection method with a heliostat type solar furnace. Quenched specimens from the melt were examined by X-ray diffraction technique, petrographic microscopy and chemical analysis.The single phase of NdAlO3 with the perovskite structure was obtained by heating at 1300 and 1600°C in an electric resistance furnace, and also by cooling the specimen fused in the solar furnace.The reversible phase transition of NdAlO3 between the rhombohedral and cubic forms was also confirmed at about 1100°C by the high temperature X-ray diffractometry. The lattice parameters of the rhombohedral phase were a0=5.351Å, α=60°10' at 1075°C, and that of the cubic phase was a0=3.792Å at 1150°C. The variation of unit cell volume ΔV was therefore only 0.42 percent.The refractive indices of NdAlO3 were obtained as γ=2.040±0.002, α=2.030±0.002.The presence of Nd2O3⋅11Al2O3 (β-Al2O3 type) was also observed. However, in a fused specimen of Nd2O3⋅11Al2O3 composition, Nd2O3⋅11Al2O3 was not formed as a single phase but always coexisted with NdAlO3.The lattice parameters of the Nd2O3⋅11Al2O3 phase were a0=5.55Å, c0=22.03Å, c/a=3.97.A tentative phase diagram for the Al2O3-Nd2O3 system at high a temperature was presented.The phase diagram shows two eutectics points at 1720°C with 23 mole percent Nd2O3, and at 1850°C with 80 mole percent Nd2O3 composition.The cooling curves of Nd2O3 showed exothermic peaks related to solid state phase transformations below the solidification point.