First-principles study of high-pressure crystal structures and superconductivity of Li_3Be alloy

摘要

Lithium alloys have attracted great interest for various structures and superconductivity under high-pressure. A pressure-induced phase transformation from previously proposed C2/m phase to a newly predicted monoclinic P2_1/c phase is observed at pressures above 92 GPa, by using particle-swarm optimization algorithms for crystal structure prediction. The application of the Allen–Dynes modified McMillan equation reveals very high superconducting temperatures (T_c) of 13–15 K and 15–18 K for the C2/m phase at 82 GPa and 90 GPa, respectively. This superconductivity mainly results from low frequency vibrations and larger electronic density of states at Fermi level. The hardening of phonon frequencies with pressure is responsible for the increased T_c in the C2/m phase. In the high pressure P2_1/c phase, superconductivity is almost vanished with T_c as low as 0.1–0.6 K at 110 GPa, and approximately independent of pressure in the range 110–120 GPa.