Heat capacity and thermal expansion coefficient of rare earth uranates RE6UO12 (RE = Nd, Gd and Eu)

Rare earth uranates Nd6UO12, Gd6UO12 and Eu6UO12 were prepared by combustion synthesis and characterized by XRD. Single-phase rhombohedral structure was observed for all the above compounds. Heat capacity measurements were carried out on Nd6UO12 and Gd6UO12 with differential scanning calorimetry in the temperature range 298-800 K. Enthalpy, entropy and Gibbs energy functions were computed. Heat capacity values of Nd6UO12 and Gd6UO12 at 298 K are 436 and 400 J K-1 mol(-1), respectively. Thermal expansion characteristics were studied using high temperature X-ray diffraction (HTXRD) in the temperature range 298-873 K. The coefficients of thermal expansion measured for Eu6UO12 are 10.5 x 10(-6) and 7.3 x 10(-6) K-1 along a- and c-axis, respectively. Similarly, the coefficients of thermal expansion of Gd6UO12 along a-axis are 10.0 x 10(-6) K-1 and along c-axis is 9.7 x 10(-6) K-1.