Prediction of high- Tc superconductivity in ternary lanthanum borohydrides

Xiaowei Liang,Xudong Wei,Xiaoxu Song,Lin Wang,Hanyu Liu,Yongjun Tian,Guoying Gao,Rongxin Sun,Russell J Hemley,Linyan Wang,Aitor Bergara

doi:10.1103/physrevb.104.134501

Abstract

The study of superconductivity in compressed hydrides is of great interest due to measurements of high critical temperatures (Tc) in the vicinity of room temperature, beginning with the observations of LaH10 at 170-190 GPa. However, the pressures required for synthesis of these high Tc superconducting hydrides currently remain extremely high. Here we show the investigation of crystal structures and superconductivity in the La-B-H system under pressure with particle-swarm intelligence structure searches methods in combination with first-principles calculations. Structures with six stoichiometries, LaBH, LaBH3, LaBH4, LaBH6, LaBH7 and LaBH8, were predicted to become stable under pressure. Remarkably, the hydrogen atoms in LaBH8 were found to bond with B atoms in a manner that is similar to that in H3S. Lattice dynamics calculations indicate that LaBH7 and LaBH8 become dynamically stable at pressures as low as 109.2 and 48.3 GPa, respectively. Moreover, the two phases were predicted to be superconducting with a critical temperature (Tc) of 93 K and 156 K at 110 GPa and 55 GPa, respectively. Our results provide guidance for future experiments targeting new hydride superconductors with both low synthesis pressures and high Tc.

Highlights

Exploration of superconductivity in materials at ever increasing temperatures is a burgeoning research topic in condensed matter physics, chemistry, and materials science
We adopted a kinetic energy cutoff of 60 Ry. 7 × 7 × 5, and 9 × 9 × 9 q-point meshes in the first Brillouin zones (BZ) were used for P3 ̄m1-LaBH7 and Fm3 ̄m-LaBH8, respectively
To understand the origin of relatively low-pressure stability of P3 ̄m1-LaBH7 and Fm3 ̄m-LaBH8, we explored the bonding of these structures by calculating the electron localization function (ELF) [52,53] and Bader charge transfer [54] among atoms

Summary

INTRODUCTION

Exploration of superconductivity in materials at ever increasing temperatures is a burgeoning research topic in condensed matter physics, chemistry, and materials science. Lower level CH4 substitution in the material, either as stoichiometric compounds or doped structures, could enhance low-pressure stability, as well as significantly enhance Tc as recently predicted for the C-S-H superconductor [30]. These results further suggest that ternary hydride systems may be a useful venue for discovering high-Tc superconductors at low pressures. Metal hydrides having clathrate and related structures (e.g., MgH6, CaH6, YH6, LaH10, and H3S) [7,8,9,10,12,13] have been predicted, and in several cases observed, to have high-Tc values that are higher than those with higher H content, such as MgH12 and MgH16 [31] This trend arises from the different forms of H atoms in the structures. Our results indicate that continued exploration of ternary hydrides in these and related chemical systems may be an effective route to realizing a high-temperature superconductivity at lower, or even ambient, pressure

COMPUTATIONAL DETAILS

RESULTS AND DISCUSSION

CONCLUSIONS