Superconductivity in Hydrides Doped with Main Group Elements Under Pressure

Abstract

A priori crystal structure prediction techniques have been used to explore the phase diagrams of hydrides of main group elements under pressure. A number of novel phases with the chemical formulas MHn, n > 1 and M = Li, Na, K, Rb, Cs; MHn, n > 2 and M= Mg, Ca, Sr, Ba; HnI with n > 1 and PH, PH 2 , PH 3 have been predicted to be stable at pressures achievable in diamond anvil cells. The hydrogenic lattices within these phases display a number of structural motifs including H δ− 2 , H − , H − 3 , as well as one-dimensional and three-dimensional extended structures. A wide range of superconducting critical temperatures, Tcs, are predicted for these hydrides. The mechanism of metallization and the propensity for superconductivity are dependent upon the structural motifs present in these phases, and in particular on their hydrogenic sublattices. Phases that are thermodynamically unstable, but dynamically stable, are accessible experimentally. The observed trends provide insight on how to design hydrides that are superconducting at high temperatures.

Potential high- T c superconducting lanthanum and yttrium hydrides at high pressure

“…In particular, the superconducting transition temperature T c calculated for LaH 10 is 274-286 K at 210 GPa. Similar calculations for the Y-H system predict stability of the sodalite-like fcc YH 10 and a T c above room temperature, reaching 305-326 K at 250 GPa. The study suggests that dense hydrides consisting of these and related hydrogen polyhedral networks may represent new classes of potential very hightemperature superconductors.…”

“…The T c of YH 10 increased by ∼30 K relative to YH 6 (30) despite the fact that λ decreases (from 2.93 to 2.56). But, this change is offset by the higher average ω log calculated for YH 10 compared with YH 6 (1,282 K versus 1,124 K), as a result of the higher hydrogen content in the former. The information of all predicted structures for La-H and Y-H is summarized in Table S2.…”

“…As Fig. 8 shows, predictably most of the states below the Fermi level are H-H bonding for LaH 10 and YH 10 . The interesting difference is that some H-H antibonding states are occupied in the yttrium hydride.…”

“…1). That result encouraged us to calculate the T c of LaH 10 . Previous theoretical studies also found that sodalite-structured hydrides (e.g., CaH 6 and YH 6 ) were associated with calculated high-T c superconductivity.…”

“…These proposals, which were based on the Bardeen-Cooper-Schrieffer (BCS) (3) phononmediated theory of superconductivity, have motivated many theoretical and experimental efforts in the search for hightemperature superconductivity in hydrides at elevated pressures (4)(5)(6)(7)(8)(9)(10). Theory has predicted the stability of a variety of dense hydride structures for which BCS arguments give superconducting transition temperatures, T c s, that are very high (11)(12)(13)(14)(15)(16)(17)(18).…”