High-temperature phase relations in the Sc2O3-Ta2O5 system

The phase relations for the Sc2O3-Ta2O5 system in the composition range of 50-100 mol% Sc2O3 have been studied by using solid-state reactions at 1350 degrees, 1500 degrees, or 1700 degrees C and by using thermal analyses up t o the melting temperatures. The Sc5.5Ta1.5O12 phase, defect-fluorite-type c ubic phase (F-phase, space group Fm3m), ScTaO4, and Sc2O3 were found in the system. The Sc5.5Ta1.5O12 phase formed in 78 mol% Sc2O3 at <1700 degrees C and seemed to melt incongruently. The F-phase formed in similar to 75 mol% Sc2O3 and decomposed to Sc5.5Ta1.5O12 and ScTaO4 at <1700 degrees C. The F -phase melted congruently at 2344 degrees +/- 2 degrees C in 80 mol% Sc2O3. The eutectic point seemed to exist at similar to 2300 degrees C in 90 mol% Sc2O3. A phase diagram that includes the four above-described phases has b een proposed, instead of the previous diagram in which those phases were no t identified.