Infrared spectroscopic study of the band-gap closure inYH3at high pressure

Abstract

Infrared vibrational absorption spectra are measured for yttrium trihydride at room temperature and pressures up to 30 GPa. The spectral change that begins near 12 GPa is interpreted in terms of a hcp-fcc structural transition, which agrees with previous x-ray diffraction measurements. For the hydrogen vibrations in the low-pressure hcp phase, the mode Grüneisen parameters are derived from the observed peak frequency shifts with pressure and the reported bulk modulus. The value of 1.91 for the octahedral-site vibration is three times larger than those for the tetrahedral-site vibrations, suggesting hybridization between the hydrogen 1s and yttrium 4d orbitals at the octahedral site. The infrared transmission spectra collapse when the high-pressure fcc phase is compressed beyond 23 GPa. The band gap abruptly closes without a structural change in the fcc metal lattice. The experimental results are in contrast to the previous theoretical calculations predicting the electronic transition either with hcp-fcc structural change or in the hcp low-pressure phase without structural change. The transition mechanism is still inconclusive.

Consecutive Peierls distortions and high-pressure phase transitions inYH3

“…Such a high Debye temperature is promising for enhanced superconductivity behavior; however, the very low DOS at the Fermi level will strongly limit its occurrence. The coexistence of high Debye temperature and low DOS at the Fermi level has been, for example, seen before in high-pressure AlH 3 , and the competition between these features results in a nonsuperconducting phase, at least down to 4 K. 30 In this respect, the question of whether the hcp and Cmcm structures are superconducting can only be answered by the experiments. The present results encourage further experimental study of YH 3 at high pressure.…”

“…1 The electronic properties of YH x hydrides can also be significantly modified by pressurization as well as hydrogenation. The insulating state of YH 3 at ambient pressure will transform to a metallic phase if the pressure is sufficient. Upon compression, the ionicity of YH 3 is decreased and a significant amount of electronic charge is transferred back to Y atoms.…”

“…Upon compression, the ionicity of YH 3 is decreased and a significant amount of electronic charge is transferred back to Y atoms. A series of studies have characterized the highpressure phase transitions for YH 3 up to 40 GPa. [2][3][4][5][6][7][8] At ambient pressure, YH 3 forms a distorted hcp form identified with space group P3c1 by neutron diffraction.…”

“…A series of studies have characterized the highpressure phase transitions for YH 3 up to 40 GPa. [2][3][4][5][6][7][8] At ambient pressure, YH 3 forms a distorted hcp form identified with space group P3c1 by neutron diffraction. [9][10][11] There are two other suggested possible structures 12,13 that are almost energetically degenerate but not in agreement with recent neutron-diffraction data.…”

High-pressure infrared spectroscopy: Tuning of the low-energy excitations in correlated electron systems

“…The pressure-driven collapse of the insulating state has been recently followed by infrared spectroscopy in the colossal magnetoresistance manganite La 1−x Ca x MnO 3 , 3 in Mott insulators such as YNiO 3 ͑Ref. 4͒ and V 3 O 5 , 5 in the band insulator YH 3 , 6 and in the chargedensity-wave rare-earth tritellurides. 3 Besides the phase transition phenomena, strong pressure-induced variation of the electronic structure has been reported for CeSb, 7 ␤-Na 0.33 V 2 O 5 , 8 silane, 9 etc.…”