Thermal expansion and athermal phase transition of Y4Al2O9 ceramics

Thermal Expansion of Y4Al2O9 ceramics prepared at 1,600 and 1,800 C was measured from room temperature to 1,500 C in air. Volume changes at the phase transition of Y4Al2O9, along with thermal hysteresis, were observed around 1,400 C. The volume of the high-temperature phase was about 0.5% lower than that of the low-temperature phase. The hysteresis width for the sample prepared at 1,600 C was 56 C, wider than that (14 C) for the sample prepared at 1,800 C. The averages of phase transition start temperatures on heating and on cooling for these samples were, however, almost the same at 1,377 C. The phase transitions did not occur at fixed temperatures, and the proportions of the high-temperature phase and the low-temperature phase did not change with time as long as the temperature remained constant (athermal character). The sample prepared at 1,800 C also showed another thermal hysteresis behavior from room temperature to about 1,000 C