Local electronic structure rearrangements and strong anharmonicity in YH3 under pressures up to 180 GPa

The discovery of superconductivity above 250 K at high pressure in LaH10 and the prediction of overcoming the room temperature threshold for superconductivity in YH10 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 YH3 under pressure up to 180 GPa. The combination of the experimental methods allowed us to implement a multiscale length study of YH3: 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.

A 92.5 K REBa2Cu3O7-δ SUPERCONDUCTOR STARTING FROM NATURAL MIXTURE OF RARE EARTH ELEMENTS

The processing and characterization of a REBa 2 Cu 3 O 7-δ, sample superconductor is described, where RE corresponds to a natural mixture of rare earth elements extracted from xenotime mineral. This mixture contains no Pr and, contrary to previous studies, can substitute the yttrium atom in YBa 2 Cu 3 O 7-δ, (YBCO) without deleterious effects in structural and superconducting properties, as measured by X-ray diffraction, resistivity and magnetoresistivity. Our sample presented T c =92.5 K and average lattice parameters a=3.821 Å, b=3.896 Å and c=11.686 Å, which are very similar to YBCO properties. Considering that the process of separation of Y (and other pure rare earth elements) from any natural mixture involves high costs, our system represents a practical alternative to YBCO compound.