High-pressure structures of yttrium hydrides

Abstract

In this work, the crystal structures of YH and YH at high pressure (100-250 GPa) have been explored using a genetic algorithm combined with first-principles calculations. New structures of YH with space group symmetries of P21/m and I4/mmm were predicted. The electronic structures and the phonon dispersion properties of various YH and YH structures at different temperatures and pressures were investigated. Among YH phases, the P21/m structure of YH was found to have a relatively high superconducting transformation temperature T of 19 K at 120 GPa, which is reduced to 9 K at 200 GPa. Other YH structures have much lower T s. Compared with YH, the T of the YH compound is much higher, i.e. 94 K at 120 GPa and 55 K at 200 GPa.

Superconductivity up to 243 K in the yttrium-hydrogen system under high pressure

“…2a ) and the c / a ratios of bct- YH 4 and hcp -YH 9 (Fig. 2b ) agree well with the theoretical predictions 22 – 24 , 26 , 31 , 32 , which justifies the assignment of compositions for the hydrides with H/Y > 3.…”

“…In addition, we did not observe superconductivity in fcc -YH 3 upon cooling down to 5 K in the pressure range of 15–180 GPa or in bct- YH 4 upon cooling down to 78 K at 250 GPa (Supplementary Fig. 4 ), while both phases were predicted to be superconductors with T c s of 40 K 51 and 84–95 K 24 , 32 , respectively.…”

“…The data for the corresponding yttrium deuterides are outlined in black. Open black circles, stars, squares and triangles correspond to the theoretically predicted structures for YH 9 22 , YH 6 22 – 24 , 26 , YH 4 22 – 24 , 26 and YH 3 31 , 32 , respectively. Experimental data for pure Y 33 , 63 , YH 3 59 , YH 4 26 and YH 6 26 taken from the literature are depicted by the red symbols.…”

“…The hydrogen network with short H-H distances in the clathrate-like structures is even closer to metallic atomic hydrogen in comparison to H3S, and can be considered as doped atomic hydrogen. The rapidly growing literature on this topic indicates that various transition metal, lanthanide or actinide elements are prone to form such superhydrides and some of them exhibits superconductivity with much higher calculated critical temperatures [4][5][6][12][13][14][15] . The experimental evidence for the record Tc of 250 K in the fcc-LaH10 at 150 GPa 2,3 has confirmed the theoretical predictions and inspired experimentalists to synthesize new members of the clathrate-like family of hydrides with promising high Tcs.…”

Novel superconducting structures of BH2 under high pressure

“…The unbiased global structural search based on GA method combined with first-principles structural relaxation is very effective to search a large structural phase space, which has been extensively applied to the structural prediction of crystals and clusters. [39][40][41] In this work, the GA search to obtain low-enthalpy structures was proceeded as follows: (i) structural search started from 40 initial random structures and these structures are relaxed by DFT calculations; (ii) using the cut-and-pasted operation, 10 offspring structures were generated based on the 40 parent structures at each GA generation; (iii) after the 10 offspring structures were fully relaxed by DFT calculations, 40 low-enthalpy structures are selected from the total 50 structures to evolve into next generation of GA. Candidate structures obtained from the GA search were further refined using the DFT calculations.…”