511 / 2019-03-19 11:22:21

Electronic structure and superconductivity in hexagonal Li3B2 and Li2B2H phases under pressure

Superconductor; Crystal structure; High-pressure; Electronic band structure; Electron-phonon interaction

全体主题 > High Pressure Physics and Materials Science

Superconductivity in layered Li–B compounds has been investigated due to the discovery of the superconductivity of MgB2 (Tc = 39 K). Hexagonal Li3B2 phase (h-Li3B2) in the Li3Al2 structure has been assumed to possess electronic features that are similar to those in MgB2 under 100 GPa, but no detailed electron–phonon coupling (EPC) analysis has been reported. In this work, layered hexagonal Li3B2 phase under 20 GPa was identified on the basis of ab initio calculations.
Inspired by the high-temperature superconductivity of metallic hydrogen, this study obtained a novel hexagonal Li2B2H (h-Li2B2H) structure by replacing Li2 with H. Contrast to h-Li3B2, h-Li2B2H may be directly synthesized by α-LiB and H2 under P = 20 GPa. The two phases exhibited electronic features similar to those in MgB2 and were expected to be good superconductors. Electron–phonon coupling calculations illustrated that the layered h-Li3B2 structure is superconducting at 2 K with λ = 0.39 under 20 GPa. Moreover, h-Li2B2H was predicted to possess a large electron–phonon coupling parameter λ of approximately 0.81 and a resulting superconducting critical temperature that reaches 28 K at 20 GPa. The introduced H in the h-Li2B2H structure had a strong vibrational energy due to its light atomic mass and could enhance the energy of σ and π bonds by bonding with Li. Thus, the introduced H in the h-Li2B2H structure is important due to its enhanced electron–phonon coupling and superconducting properties.