3 3 I H I G H L I G H T S 2 0 2 1
Fig. 20: a) Pressure dependences of pair radial distribution function (PRDF) of the first Y(0)-Y(1) shell at different pressures
up to 176 GPa. b) Pressure evolution of the mean square relative displacement (MSRD) for the three nearest Y-Y shells
around Y(0) atoms. c) Double-well vibrational potential of Y atoms at 176 GPa.
PRINCIPAL PUBLICATION AND AUTHORS
Local electronic structure rearrangements and strong anharmonicity in YH3 under pressures up to 180 GPa, J. Purans (a,b), A.P. Menushenkov (b), S.P. Besedin (c), A.A. Ivanov (b), V.S. Minkov (c), I. Pudza (a), A. Kuzmin (a), K.V. Klementiev (d), S. Pascarelli (e,f), O. Mathon (e), A.D. Rosa (e), T. Irifune (g), M.I. Eremets (c), Nat. Commun. 12, 1765 (2021); https:/doi.org/10.1038/s41467-021-21991-x (a) Institute of Solid State Physics University of Latvia, Riga (Latvia) (b) National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), Moscow (Russia) (c) Max-Planck Institut für Chemie, Mainz (Germany) (d) MAX IV Laboratory, Lund (Sweden) (e) ESRF (f) European X-Ray Free Electron Laser (XFEL) GmbH, Schenefeld (Germany) (g) Geodynamics Research Center, Ehime University, Matsuyama (Japan)
 A.P. Drozdov et al., Nature 525, 73-76 (2015).  A.P. Drozdov et al., Nature 569, S28 (2019).  P. Kong et al., Nat. Commun. 12, 5075 (2021).  H. Liu et al., Proc. Natl. Acad. Sci. U.S.A. 114, 6990 (2017).  Y. Sun et al., Phys. Rev. Lett. 123, 097001 (2019).
The combination of the experimental methods made it possible to implement a multiscale length study of YH3, covering short-, medium- and long-range. X-ray absorption near-edge structure (XANES) data demonstrate 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. The crystal lattice instability arising due to the Jahn- Teller effect was found to manifest itself as local (short- range) lattice distortions, which inhibit superconductivity in YH3 at low pressures. That, in turn, reconciles many controversies observed previously in this compound and provides valuable information concerning the nearly room-temperature superconductivity recently found at high pressures. These results will contribute to a better understanding of the hydrogen interaction mechanism with the heavy atom sublattice and high-temperature superconductivity in metal hydrides.
More recently, yttrium hydrides with the compositions of YH6 and YH9 were synthesised in a diamond anvil cell, and superconductivity in the YH6 and YH9 phases was demonstrated with a maximal Tc of ~220 K at 183 GPa and ~243 K at 201 GPa, respectively. Further work at beamline BM23 has focused on carrying out XRD and XAS measurements on these samples under ultrahigh pressure.