Prediction of Li2B novel phases and superconductivity under varying pressures.

Graphical abstract Highlights • Three novel Li 2 B phases are proposed. • These Li 2 B phases are more energy stable than Cmcm -Li 2 B at ambient pressure. • oC12–Li 2 B may be experimentally synthesized under ambient pressure. • hP6–Li 2 B has potential superconductivity. Abstract Few experimental and theoretical superconductivity works have focused on Li–B systems under the Li-rich regime. Here, we utilized the recently developed particle-swarm optimization method for structural search to propose three novel Li 2 B phases. These phases include the layered sandwich structure hP6–Li 2 B (P-3m1 , 164) and the two chain structures mS12–Li 2 B (C2/m , 12) and oC12–Li 2 B (Cmcm , 63). The structural stability of the three novel Li 2 B phases was confirmed on the basis of elastic constant and phonon dispersion calculations. Under ambient pressure, the three Li 2 B structures are notably more thermodynamically stable than the previously proposed Cmcm -Li 2 B structure and oC12–Li 2 B may be experimentally synthesized by α -LiB and Li. Electronic band structure and partial density of states analyses showed that our three proposed phases were metallic. The quasi-2D character in the band structure of hP6–Li 2 B was consistent with that of MgB 2 and indicated that hP6–Li 2 B has potential superconductive properties. Our electron–phonon coupling calculations illustrated that mS12– and oC12–Li 2 B exhibited superconductivity at 0.03 K under 10 Gpa and 0.14 K under 0 Gpa, respectively. Moreover, we found that hP6–Li 2 B has low superconductivity with a predicted T c of 0.09 K at 20 GPa, and its λ and T c values increased within the pressure range of 20–50 GPa and then decreased under pressures exceeding 60 GPa. The maximum λ and T c values under 60 GPa were 0.33 and 0.65 K, respectively. [ABSTRACT FROM AUTHOR]