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 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→P2 1 /m→R 3 m 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→P4/mmm→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 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.