Ultra-fast yttrium hydride chemistry at high pressures via non-equilibrium states induced by x-ray free electron laser

TL;DR

This study demonstrates ultra-fast synthesis of a metastable yttrium hydride with variable hydrogen content at high pressures using x-ray free electron laser pulses, revealing a new approach to controlling material phases via non-equilibrium pathways.

Contribution

It introduces a novel method for synthesizing and tuning yttrium hydrides under high pressure using XFEL-induced non-equilibrium states, enabling access to metastable phases not achievable with conventional methods.

Findings

Synthesized a new yttrium hydride phase at 125 GPa.

Achieved control over hydrogen content via x-ray fluence adjustments.

Discovered a metastable hydride with an A15 structure type.

Abstract

Controlling the formation and stoichiometric content of desired phases of materials has become a central interest for the study of a variety of fields, notably high temperature superconductivity under extreme pressures. The further possibility of accessing metastable states by initiating reactions by x-ray triggered mechanisms over ultra-short timescales is enabled with the development of x-ray free electron lasers (XFEL). Utilizing the exceptionally high brilliance x-ray pulses from the EuXFEL, we report the synthesis of a previously unobserved yttrium hydride under high pressure, along with non-stoichiometric changes in hydrogen content as probed at a repetition rate of 4.5\,MHz using time-resolved x-ray diffraction. Exploiting non-equilibrium pathways we synthesize and characterize a hydride with yttrium cations in an \textit{A}15 structure type at 125\,GPa, predicted using crystal structure searches, with a hydrogen content between 4.0--5.75 hydrogens per cation, that is enthalpically metastable on the convex hull. We demonstrate a tailored approach to changing hydrogen content using changes in x-ray fluence that is not accessible using conventional synthesis methods, and reveals a new paradigm in metastable chemical physics.