High-Tc Superconducting Hydrides Formed by LaH_(24) and YH_(24) Cage Structures as Basic Blocks

摘要

Based on recent studies regarding high-temperature (high-Tc) La-Y ternary hydrides (e.g., Pl-La2YH_(12), Pm3m-LaYH_(12), and Pm3m-(La,Y)H_(10) with a maximum Tc ～ 253 K), we examined the phase and structural stabilities of the (LaH6)(YH6) series as high-Tc ternary hydride compositions using a genetic algorithm and ab initio calculations. Our evaluation showed that Pm3m-LaYH_(12) reported in the previous study was unstable during decomposition into R3c-LaH6 + Im3m-YH6. We also discovered new crystal structures, namely, Cmmm-LaYH_(12) (y = 1), R3c-LaYH_(12) (y = 1), Cmmm-LaY3H_(24) (y = 3), and R3-LaY3H_(24) (y = 3), showing stability against such decomposition. While R3c (y = 1) and R3 (y = 3) did not exhibit superconductivity owing to the extremely low density of states at the Fermi level, Cmmm phases exhibited a Tc of approximately 140 K at around 200 GPa owing to the extremely high electron-phonon coupling constant (λ = 1.876 for LaYH_(12)). By the twice longer stacking for Cmmm-LaY3H_(24), the coupling constant increased owing to the chemical pressure of Y, leading to a slightly increased Tc.