Phase Equilibrium Relations in the Sc(2)O(3)-Ga(2)O(3) System

The phase equilibrium diagram was determined for the Sc(2)O(3)-Ga(2)O(3) 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 Ga(2)O(3) was determined as 1,795 ±15 °C. Experiments at temperatures as high as 2,405 °C failed to melt Sc(2)O(3). Two intermediate binary phases, a compound believed to be 6Sc(2)O(3)·5Ga(2)O(3) 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 Ga(2)O(3) 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.