Local electronic structure rearrangements and strong anharmonicity in YH under pressures up to 180 GPa.

The discovery of superconductivity above 250 K at high pressure in LaH and the prediction of overcoming the room temperature threshold for superconductivity in YH urge for a better understanding of hydrogen interaction mechanisms with the heavy atom sublattice in metal hydrides under high pressure at the atomic scale. Here we use locally sensitive X-ray absorption fine structure spectroscopy (XAFS) to get insight into the nature of phase transitions and the rearrangements of local electronic and crystal structure in archetypal metal hydride YH under pressure up to 180 GPa. The combination of the experimental methods allowed us to implement a multiscale length study of YH: XAFS (short-range), Raman scattering (medium-range) and XRD (long-range). XANES data evidence a strong effect of hydrogen on the density of 4d yttrium states that increases with pressure and EXAFS data evidence a strong anharmonicity, manifested as yttrium atom vibrations in a double-well potential.