Modeling Superionic Behavior of Plutonium Dioxide

TL;DR

This paper develops a molecular dynamics model to simulate the superionic transition in plutonium dioxide, successfully reproducing the Bredig transition and associated thermophysical properties around 2100K, addressing previous experimental uncertainties.

Contribution

A new molecular dynamics model for PuO2 that accurately predicts the superionic transition and thermophysical behavior, resolving past experimental ambiguities.

Findings

Successful observation of the Bredig transition at ~2100K in simulations.

Reproduction of experimental enthalpy changes across the transition.

Validation of the model's thermophysical property predictions.

Abstract

The Bredig transition to the superionic phase indicated with the lambda-peak in Cp was highly expected for PuO2 as other actinide dioxides. However, least-square fit and local smoothing techniques applied to the experimental enthalpy data of plutonium dioxide in 80's could not detect a 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 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 lambda-peak in specific heat was a successfully observed for the model system at about 2100K. Moreover, the experimental enthalpy change was well reproduced before and after the estimated transition temperature.