Thermal expansion measurement and heat capacity evaluation of hypo-stoichiometric PuO2.00

Linear thermal expansion of hypo-stoichiometric plutonium dioxide was measured between 1673 K and 1923 K by dilatometry in a controlled oxygen partial pressure, as a function of temperature and oxygen-to-metal ratio. Coefficients for second-order polynomials expressing the thermal expansion coefficient were obtained. Heat capacity of PuO2−x, with 0 < x < 0.08, was also evaluated using the current thermal expansion coefficient. The measured expansion of PuO2−x was found to slightly increase with the deviation from stoichiometry x. The observed O/M ratio effect on heat capacity was small. Experimental heat capacity data are better explained at high temperatures when a term taking into account Schottky type heat capacity is added to the vibrational and dilatational terms.