High-Tc Superconducting Hydrides Formed by LaH24 and YH24 Cage Structures as Basic Blocks

Abstract

Based on recent studies regarding high-temperature (high-Tc) La–Y ternary hydrides (e.g., P1̅-La2YH12, Pm3̅m-LaYH12, and Pm3̅m-(La,Y)H10 with a maximum Tc ∼ 253 K), we examined the phase and structural stabilities of the (LaH6)(YH6)y series as high-Tc ternary hydride compositions using a genetic algorithm and ab initio calculations. Our evaluation showed that Pm3̅m-LaYH12 reported in the previous study was unstable during decomposition into R3̅c-LaH6 + Im3̅m-YH6. We also discovered new crystal structures, namely, Cmmm-LaYH12 (y = 1), R3̅c-LaYH12 (y = 1), Cmmm-LaY3H24 (y = 3), and R3̅-LaY3H24 (y = 3), showing stability against such decomposition. While R3̅c (y = 1) and R3̅ (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 LaYH12). By the twice longer stacking for Cmmm-LaY3H24, the coupling constant increased owing to the chemical pressure of Y, leading to a slightly increased Tc