X-ray Debye temperature and Grueneisen constant of NpO2

The Debye temperature, ΘD, and the Grueneisen constant, γ, are useful parameters to estimate thermal properties of ceramics. In the present study, those for NpO2 were determined through a high-temperature X-ray diffraction analysis. The measurements were carried out in the temperature range from room temperature up to 1174 K. The temperature factor of Np at each measured temperature was refined by Rietveld analysis to obtain ΘD, assuming that the factor of O is the same as in UO2. The calculated ΘD values tended to decrease with increasing temperature, which was attributed to the anharmonicity of lattice vibration. From the decrease, we determined γ using Paskin's temperature calibration which corrects the effect of anharmonicity. The values of ΘD and γ obtained in this study were 435±2 K and 1.93±0.03, respectively. (orig.)