High-temperature phase transition of Y4Al2O9

Reversible thermal phase transition was observed for Y4Al2 O9 at 1377°C with a hysteresis width of 78°C using differential scanning calorimetry. The enthalpy of the transition (ΔH) was about 300 cal/mol. Powder X-ray diffraction peaks of the high temperature phase, as well as the peaks of the low-temperature phase, were characterized with a monoclinic unit cell. Thermal hystersis was also confirmed by the temperature dependence of the lattice parameter. The unit cell column of the high-temperature phase was 0.5% smaller than that of the low-temperature phase at 1400°C.