Heat Capacity and Thermodynamic Functions of the Y2O3·2HfO2 Solid Solution

A single-phase yttrium hafnate sample of the composition Y2O3⋅2HfO2 was synthesized by reverse coprecipitation and identified by scanning electron microscopy and X-ray diffraction. The isobaric heat capacity was measured using adiabatic calorimetry (9–347 K) and differential scanning calorimetry (317–1877 K). The temperature dependences of the thermodynamic functions (entropy, enthalpy increment, and reduced Gibbs energy) were determined from the smoothed heat capacity values. The entropy value predicted by the model for the solid solution was not confirmed, which may be due to an insufficiently correct model description of the ordering in the structure of the Y2O3⋅2HfO2 solid solution.