A High Pressure Distorted a-Uranium (Pnma) Structure in Plutonium

TL;DR

This paper reinterprets diffraction data to reveal that high-pressure phases of plutonium adopt a distorted orthorhombic structure similar to a-U, explaining volume anomalies and structural transformations.

Contribution

It introduces a new interpretation of plutonium's high-pressure structure as a distorted a-U type in Pnma space group, expanding understanding of actinide phase behavior.

Findings

High-pressure Pu has a distorted a-U (Pnma) structure.

The structure exhibits a distorted hcp topology.

Atomic volume increase at 0.1 MPa is explained by this model.

Abstract

Under pressure many rare earths and actinide metals transform to a-U structure or its lower symmetry distorted forms. We have reinterpreted the diffraction data of Dabos et al for Pu (reference 4) and find that a Am IV type distorted a-U structure in Pnma space group can explain this for its high pressure phase. The structures of this phase and a-Pu are both shown to have a distorted hcp topology. The upturn in the atomic volume of Pu at 0.1 MPa can also be rationalized on the basis of this proposal