Phase equilibrium relations in the Sc2O3-Ga2O3 system

Abstract

The phase equilibrium diagram was determined for the Sc2O3-Ga2O3 system. A quenching furnace, wound with 60 percent Pt-40 percent Rh wire, was employed for experiments conducted at temperatures up to 1,800 °C. An induction furnace, having an iridium crucible susceptor, was used to obtain higher temperatures. Temperatures in the quenching furnace were measured with both an optical pyrometer and a 95 percent Pt-5 percent Rh versus 80 percent Pt-20 percent Rh thermocouple. The melting point of Ga2O3 was determined as 1,795 ± 15 °C. Experiments at temperatures as high as 2,405 °C failed to melt Sc2O3. Two intermediate binary phases, a compound believed to be 6Sc2O3 · 5Ga2O3 and a solid solution occur in the system. The solid solution phase appears as a single phase in the region roughly defined by the compositional limits of 55 to 73 mole percent Ga2O3 at the solidus. The 6 : 5 compound, stable only at high temperatures, melts incongruently at 1,770 ± 15 °C and decomposes below 1,700 ± 15 °C. The compound appears to have orthorhombic symmetry with a = 13.85 A, b = 9.80 A, and c = 9.58 A. The indicated uncertainties in the melting points are a conservative estimate of the overall inaccuracies.