First-principles study on stability and superconductivity of ternary hydride LaYH x (x = 2, 3, 6 and 8)

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 LaYH2 stablizes in the C2/m phase at ambient pressure, and transforms to the Pmmn phase at 67 GPa. LaYH3 stablizes in the C2/m phase at ambient pressure, and undergoes a phase transition of C2/m→P21/m→R3m at 12 and 87 GPa, respectively. LaYH6 stablizes in the P43212 phase at ambient pressure, and undergoes a phase transition of P43212→P4/mmm→ Cmcm at 28 GPa and 79 GPa, respectively. LaYH8 stablizes 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-LaYH8 and all phases of LaYH2 and LaYH3 exhibt metallic character. For the metallic phases, we then study their superconducting properties. The calculated superconducting transition temperatures (Tc ) are 0.47 K for C2/m-LaYH2 at 0 GPa, 0 K for C2/m-LaYH3 at 0 GPa, and 55.51 K for P4/mmm-LaYH8 at 50 GPa, respectively.