Heat capacity of (Hf1−yAly)O0.17 at high temperature

Heat capacities of (Hf1−yAly)O0.17 (y=0–0.03) were measured from 325 to 905 K by using an adiabatic scanning calorimeter. A heat capacity anomaly was observed around 700 K for all (Hf1−yAly)O0.17 samples and assigned to an order–disorder rearrangement of oxygen atoms. The experimental transition temperatures, the enthalpy change and entropy changes due to the order–disorder transition decreased with increasing aluminium contents. The experimental entropy changes of the order–disorder transition are compared with the theoretical values from the view point of statistical thermodynamics and are discussed.