Powder x-ray diffraction data of yttria (Y2O3) were obtained from room temp
erature to melting point with the thin wire resistance heating technique. A
solid-state phase transition was observed at 2512 +/- 25 K and melting of
the high-temperature phase at 2705 +/- 25 K. Thermal expansion data for alp
ha-Y2O3 (C-type) are given for the range 298-2540 K. The unit cell paramete
r increases nonlinearly, especially just before the solid-state transition.
The x-ray diffraction spectrum of the high-temperature phase is consistent
with the fluorite-type structure (space group Fm3) with a refined unit cel
l parameter a = 5.3903(6) Angstrom at 2530 K. The sample recrystallized rap
idly above 2540 K, and above 2730 K, all the diffraction lines and spots di
sappeared from the x-ray diffraction spectrum that suggests complete meltin
g.