Pressure-induced superconductivity in H2-containing hydride PbH4(H2)2

Abstract

High pressure structure, stability, metallization, and superconductivity of PbH4(H2)2, a H2-containing compound combining one of the heaviest elements with the lightest element, are investigated by the first-principles calculations. The metallic character is found over the whole studied pressure range, although PbH4(H2)2 is metastable and easily decompose at low pressure. The decomposition pressure point of 133 GPa is predicted above which PbH4(H2)2 is stable both thermodynamically and dynamically with the C2/m symmetry. Interestedly, all hydrogen atoms pairwise couple into H2 quasi-molecules and remain this style up to 400 GPa in the C2/m structure. At high-pressure, PbH4(H2)2 tends to form the Pb-H2 alloy. The superconductivity of Tc firstly rising and then falling is observed in the C2/m PbH4(H2)2. The maximum of Tc is about 107 K at 230 GPa. The softening of intermediate-frequency phonon induced by more inserted H2 molecules is the main origin of the high Tc. The results obtained represent a significant step toward the understanding of the high pressure behavior of metallic hydrogen and hydrogen-rich materials, which is helpful for obtaining the higher Tc.

Phase stability and superconductivity of lead hydrides at high pressure

“…Full enthalpy curves including possible decomposition reactions for PbH 4 , PbH 6 and PbH 8 as function of pressure are shown in Figure 1. The stable struc-tures of Pb, H 2 , PbH, and PbH 2 were taken from previously reported work 31,44,45 , in addition to the structures predicted in this work, previously reported stable structures of PbH 4 (space groups Imma, P 2 1 /m and Ibam, labelled VII, IIa, and VIII in 25 ) and PbH 8 (C2/m, P1 and P nnm in 31 ) were also taken into consideration. We also constructed the convex hulls (see Figure 2a) by using formation enthalpies for the most favorable structure of each compound relative to elemental Pb and H 2 to determine energic stability.…”

“…The measured Raman and IR spectra for SiH 4 (H 2 ) 2 28 and GeH 4 (H 2 ) 2 30 revealed strong intermolecular interactions between SiH 4 (GeH 4 ) and H 2 at low pressure, which are demonstrated as the main reason for the predicted high-T c superconductivity in Ccca-SiH 4 (H 2 ) 2 26 , while Zhong et al mainly attributed the superconductivity in P 2 1 /c-GeH 4 (H 2 ) 2 27 to the vibrations of H 2 units. In the Pb-H system, Cheng et al 31 combined extensive structural searches and electronphonon coupling (EPC) calculations for PbH 4 (H 2 ) 2 and proposed three thermodynamically stable phases, where the C2/m phase has T c of 107 K at 230 GPa. However, in contrast to all lighter group-IVa elements, lead does not form stable XH 4 molecules, and its hydrides seem to contain H 2 molecules only.…”

The Search for Superconductivity in High Pressure Hydrides

“…CSP techniques have also been employed to investigate the PbH 4 (H 2 ) 2 stoichiometry. 296 Enthalpically stable structures, which contained H 2 molecules that separated the Pb atoms, were predicted above 133 GPa. The C2/m symmetry phase illustrated in Fig.…”

“…Unit cells of superconducting phases predicted for group 14 hydrides with the MH 4 (H 2 ) 2 stoichiometry: (a) Ccca-SiH 4 (H 2 ) 2 phase with T c = 98-107 K at 250 GPa,281 (b) P 2 1 /c-GeH 4 (H 2 ) 2 phase with T c = 76-90 K at 250 GPa,294 (c) I4m2-SnH 8 phase with T c = 63-72 K at 250 GPa 295 and (d) C2/m-PbH 4 (H 2 ) 2 phase with T c ≈ 107 K at 230 GPa 296. …”

Superconductivity of boron-doped graphane under high pressure

“…4 (b) and (c)) induced by pressure. The pressure-induced phonon soening is a common behavior of superconductors at high pressure, [35][36][37] and it plays a crucial role in enhancing the electron-phonon coupling. 1,38,39 Therefore, the l of phase-b increases with the pressure increasing, which counteracts the decrease of u log .…”