Thermodynamic properties of rubidium niobium tungsten oxide

Abstract

In the present work temperature dependence of heat capacity of rubidium niobium tungsten oxide has been measured first in the range from 7 to 395 K and then between 390 and 650 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity $C_{\text{p}}^{\text{o}} (T),$ enthalpy $H^{\text{o}} ({\rm T}) - H^{\text{o}} (0)$, entropy $S^{\text{o}} (T) - S^{\text{o}} \left( 0 \right)$, and Gibbs function $G^{{^{\text{o}} }} ({\rm T}) - H^{{^{\text{o}} }} (0)$, for the range from T→0 to 650 K. The high-temperature X-ray diffraction and the differential scanning calorimetry were used for the determination of temperature and decomposition products of RbNbWO₆.