X-ray diffraction investigation of the hexagonal–fcc structural transition in yttrium trihydride under hydrostatic pressure

Consecutive Peierls distortions and high-pressure phase transitions inYH3

“…Once the C2 / m structure completely changes to fcc at 38 GPa, the band gap closes completely and YH 3 becomes metallic. The pressure-dependent insulating properties of the C2 / m structure agree well with the experimental observation [4][5][6][7] for the intermediate phase in this pressure range.…”

“…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.…”

“…14,15 The ambient-pressure structure is shown to transform to the fcc structure over a large pressure span ranging from about 9 to 24 GPa. [4][5][6][7][8] There are experimental evidences showing an intermediate phase in this transition but the precise characterization of this structure is under debate. 4,7 During the phase transition, the band gap in YH 3 starts to narrow in the intermediate phase and closes once the structure completely transforms into fcc.…”

Ammonia as a case study for the spontaneous ionization of a simple hydrogen-bonded compound

“…5), the transition from the molecular to the ionic phases involves a shift of closed packed planes: it thus resembles the well-known reversible hcp-to-fcc phase transition observed in relatively simple (for example, noble gases 28 ) and more complex systems (yttrium and other lanthanide trihydrides 29,30 ). Indeed, the experimentally observed continuous character of the intensity change of the hkl(020) (molecular) and the hkl(210) (ionic) reflections (Fig.…”

Metal Hydrides under High Hydrostatic Pressure

“…Recently the interest to high pressure studies of yttrium and rare earth hydrides resulted in number of publications. [64][65][66][67][68][69][70] 70 . Values of bulk modulus K 0 for hcp YH 3 given in both papers differ markedly (142 GPa from Palasyuk 65 and 72 GPa from Machida 70 ).…”