Crystal structure and thermodynamic properties of cesium tantalum tungsten oxide

In the present work temperature dependence of heat capacity of cesium tantalum tungsten oxide has been measured first in the range from 7 to 350 K and then between 330 and 630 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity Cp°Cp° (T), enthalpy H°(T) − H°(0), entropy S°(T) − S°(0) and Gibbs function G°(T) − H°(0), for the range from T → 0 to 630 K. The structure of CsTaWO6 is refined by the Rietveld method: space group Fd3m, Z = 8, a = 10.3793(2) Å, V = 1118.14(4) Å3. The high-temperature X-ray diffraction was used for the determination of temperature of phase transition and coefficient of thermal expansion.