关键词: superconductivity, high pressure, first-principles study, phase transitions

Abstract: Recent studies have shown that the La- and Y-hydrides can exhibit significant superconducting properties under high pressures. In this paper, we investigate the stability, electronic and superconducting properties of LaYH$_{x}$ ($x=2$, 3, 6 and 8) under 0-200 GPa. It is found that LaYH$_{2}$ stabilizes in the $C2/m$ phase at ambient pressure, and transforms to the $Pmmn$ phase at 67 GPa. LaYH$_{3}$ stabilizes in the $C2/m$ phase at ambient pressure, and undergoes phase transitions of $C2/m\to P2_{1}/m\to R3m$ at 12 GPa and 87 GPa, respectively. LaYH$_{6}$ stabilizes in the $P4_{3}2_{1}2$ phase at ambient pressure, and undergoes phase transitions of $P4_{3}2_{1}2\to P4/mmm \to Cmcm$ at 28 GPa and 79 GPa, respectively. LaYH$_{8}$ stabilizes in the $Imma$ phase at 60 GPa and transforms to the $P4/mmm$ phase at 117 GPa. Calculations of the electronic band structures show that the $P4/mmm$-LaYH$_{8}$ and all phases of LaYH$_{2}$ and LaYH$_{3}$ exhibit metallic character. For the metallic phases, we then study their superconducting properties. The calculated superconducting transition temperatures ($T_{\rm c}$) are 0.47 K for $C2/m$-LaYH$_{2}$ at 0 GPa, 0 K for $C2/m$-LaYH$_{3}$ at 0 GPa, and 55.51 K for $P4/mmm$-LaYH$_{8}$ at 50 GPa.

Key words: superconductivity, high pressure, first-principles study, phase transitions