Structural behavior of uranium dioxide under pressure by LSDA+U calculations

TL;DR

This study uses LSDA+U calculations to explore the high-pressure structural transitions of uranium dioxide, predicting phase changes, an isostructural transition, and a metallic state at extreme pressures, aligning well with experimental data.

Contribution

First-principles LSDA+U calculations reveal detailed pressure-induced phase transitions and electronic changes in UO2, including a predicted isostructural transition not yet observed experimentally.

Findings

Structural transition to cotunnite phase at 38 GPa

Predicted isostructural transition between 80 and 130 GPa

Metallic and paramagnetic transition beyond 226 GPa

Abstract

The structural behavior of UO2 under high pressure up to 300GPa has been studied by first-principles calculations with LSDA+U approximation. The results show that a pressure-induced structural transition to the cotunnite-type (orthorhombic Pnma) phase occurs at 38GPa. It agrees well with the experimentally observed ~42 GPa. An isostructural transition following that is also predicted to take place from 80 to 130GPa, which has not yet been observed in experiments. Further high compression beyond 226GPa will result in a metallic and paramagnetic transition. It corresponds to a volume of 90A^3 per cell, in good agreement with a previous theoretical analysis in the reduction of volume required to delocalize 5f states.