Enthalpy and heat capacity of the actinide oxides

The estimation of the heat capacity of NpO2

“…In case of UO 2 , the anomalous increase in C p,m at temperatures higher than T = 1400 K due to the enthalpy of defect formation has been identified by several researchers. (19)(20)(21)(22)(23)(24)(25) The development of anion defect in UO 2 has been confirmed above T = 2000 K by neutron diffraction and coherent diffuse scattering study. (21) A similar process of defect formation might occur in NpO 2 .…”

Thermophysical properties and oxygen transport in the (U ,Pu1−)O2 lattice

“…For UO 2 there is a deviation from linear thermal expansion and a classical Debye description of the constant pressure specific heat above 1300 K [11][12][13][14][15][16][17][18][19][20]. At 2670 K (0.85T m ) there is a peak in the specific heat due to a premelting transition or superionic transition as seen in other fluorite structures [11].…”

Modeling Superionic Behavior of Plutonium Dioxide

“…Further increase in temperature results with the additional increase in calculated Cp and a λ shape peak is clearly produced at the critical temperature Tc=2055 K which is close to the expected value of the phase transition temperature in fluorite type of ionic crystals [7]. In order to make sure that it is a  -peak transition in specific heat, we have increased the number of data by varying the temperature at 50K intervals in NPT-ensemble Figure 7 as inset.…”

“…At about 2100 K, there is a sign of a change in trend of the evaluation of the data with temperature. As recommended by Fink [7] transition to the superionic phase may be expected at temperature between 2160-2370 K. is presented in Figure 6 and compared with the experimental data taken from Fink [7] and MD simulation with shell model potential by Chu.…”