Phase diagram study and thermodynamic assessment of the Y2O3-YF3 system

The phase diagram of the Y2O3-YF3 system up to 1973 K was investigated using a classical equilibration/quenching experiment and differential thermal analysis (DTA). Equilibrium phases were confirmed by electron probe microanalysis (EPMA) and X-ray diffraction (XRD) phase analysis. For the very first time, the entire range of the phase diagram of yttrium oxy-fluoride system up to 1973 K was experimentally determined. Cubic-Y2O3 phase dissolves more than 5 mol% of YF3 at 1973 K. The melting points of YOF and vernier phases are found to be higher than 1973 K and their steep liquidus in the YF3-rich region are determined. Based on new experimental phase diagram data and thermodynamic property data in the literature, the Y2O3-YF3 system was thermodynamically modeled by the CALculation of PHAse Diagram (CALPHAD) method. As applications of the thermodynamic database, metastable solubilities of YF3 in Y2O3 during plasma etching process were calculated.