Structure and Phase Transitions of Metastable Hexagonal Uranium Thin Films

TL;DR

This study presents a straightforward method to synthesize metastable hexagonal uranium thin films and investigates their structural transitions into orthorhombic uranium, revealing transition mechanisms influenced by initial lattice parameters.

Contribution

The paper introduces a simple synthesis technique for metastable hexagonal uranium films and maps their phase transition pathways, highlighting the influence of initial lattice parameters on transition mechanisms.

Findings

Metastable hexagonal uranium films were successfully synthesized.

Transition pathways depend on initial lattice parameters.

Transitions occur on specific timescales influenced by initial structure.

Abstract

We report a simple technique for the synthesis of uniaxially textured, metastable hexagonal close-packed-like uranium thin films with thicknesses between 175-2800 \r{A}. The initial structure and texture of the layers have been studied via X-ray diffraction and reflectivity and the time-dependent transitions of the samples into various orientations of orthorhombic ${\alpha}$-U have been mapped by similar techniques. The final crystallographic orientations of each system and the timescales on which the transitions occur are found to depend on the lattice parameters of the original layer. The absence of the ${\alpha}$-U (001) orientation in the transition products suggests that the transitions in these layers are mediated by mechanisms other than the [110] transverse acoustic phonon mode previously suggested for the cubic ${\gamma}$-U(110) to hcp-U(00.1) to ${\alpha}$-U(001) displacive phase transition. Alternative transition pathways are discussed.