Modeling Superionic Behavior of Plutonium Dioxide

Abstract

The Bredig transition to the superionic phase indicated with the λ$$\lambda $$-peak in Cp$${C_p}$$ was highly expected for plutonium dioxide (PuO2$${\rm{Pu}}{{\rm{O}}_2}$$) as other actinide dioxides. However, least-square fit and local smoothing techniques applied to the experimental enthalpy data of PuO2 in 1980s could not detect a λ$$\lambda $$-peak in specific heat that might be due to too scattered and insufficient experimental data. Therefore, this issue has not been yet put beyond the doubts. In the current article, a superionic model of PuO2$${\rm{Pu}}{{\rm{O}}_2}$$ is developed with partially ionic model of a rigid ion potential. Thermophysical properties were calculated in constant pressure–temperature ensemble using molecular dynamics simulation. The Bredig transition with vicinity of a λ$$\lambda $$-peak in specific heat was successfully observed for the model system at about 2,100 K. Moreover, the experimental enthalpy change was well reproduced before and after the estimated transition temperature.

Keywords

• superionic
• diffusion
• thermal properties
• mechanical properties
• plutonium dioxide