On the phase diagram of the binary system Sc2O3-ScF3 in the temperature range 1400-1840 K

The phase diagram of the binary system Sc2O3-ScF3 was investigated in the temperature range 1400-1840 K by quantitative differential thermal analysis (DTA). X-ray powder diffraction analysis revealed that at room temperature only the well-known compounds Sc2O3, ScOF and ScF3 exist. At 1419+/-3 K, the slightly non-stoichiometric compound of composition Sc(O,F)(1.88+/-delta) is probably formed by eutectoid reaction from Sc2O3 and ScOF. ScOF decomposes into Sc(O,F)(1.88+/-delta)(s) and ScF3(s) at 1460 +/- 3 K. Eutectic melting occurs at 1627 +/- 3 K for a mixture of 67 mol% ScF3 and 33 mol% ScO1.5. Pure ScF3 melts at 1822 +/- 3 K and does not display any solid state phase transition. The compound Sc(O,F)(1.88+/-delta) could not be quenched to room temperature, and therefore structural details of this presumably fluorite-related phase could not be investigated.