XRD observation of the superionic transition in UH8

This proposal aims to observe the superionic transition in a uranium superhydride, UH8, chosen for its potential superionic transition and as a below-100 GPa synthesized superhydride [3]. The superionic transition is expected to manifest as a crossover with significant thermal expansion near it, leading to a Schottky-like bump in the linear thermal coefficient [4]. This transition is also expected to stabilize UH8 at a very high temperature due to the configurational entropy of the disordered hydride ions. Observing UH8 melting temperature closely matching that of pure U, whereas the melting of UH3 and UH7 would be at a significantly lower temperature than pure U, would also indirectly demonstrate the superionic state.
XRD measurements of UH3, UH7 and UH8 in a laser-heating DAC will be conducted by following isobaric thermal ramps. Ongoing ab initio simulations will support experimental findings.