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 stabilizes in the C2/m phase at ambient pressure, and transforms to the Pmmn phase at 67 GPa. LaYH₃ stabilizes in the C2/m phase at ambient pressure, and undergoes phase transitions of C2/m → P2₁/m → R3m at 12 GPa and 87 GPa, respectively. LaYH₆ stabilizes in the P4₃2₁2 phase at ambient pressure, and undergoes phase transitions of P4₃2₁2 → P4/mmm → Cmcm at 28 GPa and 79 GPa, respectively. LaYH₈ 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-LaYH₈ and all phases of LaYH₂ and LaYH₃ 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-LaYH₂ at 0 GPa, 0 K for C2/m-LaYH₃ at 0 GPa, and 55.51 K for P4/mmm-LaYH₈ at 50 GPa.