Prediction of pressure-induced superconductivity in the ternary systems CaYH2n (n = 3–6) at moderate pressures

Abstract

Hydrogen-rich ternary compounds are regarded as promising candidates for room-temperature superconductivity, primarily due to the synergistic effects of their crystal structures and electronic properties under high-pressure conditions. However, the vast chemical space of these compounds is vast, making its exploration particularly challenging. In this study, we explore the high-pressure structures, electronic characteristics, and superconducting behavior of the ternary calcium–yttrium–hydrogen (Ca–Y–H) system using a predictive approach that combines particle swarm optimization (PSO) with first-principles calculations. Our research identifies four stable structures, each characterized by a unique hydrogen sublattice arrangement: Pmmm-CaYH₆, P4/mmm-CaYH₈, Cmmm-CaYH₁₀, and Fdm-CaYH₁₂. All predicted Ca–Y–H structures exhibit characteristics of high-temperature superconductors. The electron localization function (ELF) analysis reveals no significant interaction between hydrogen atoms in the CaYH₆ compound, while the other stoichiometric compositions show weak H–H covalent interactions. Notably, CaYH₆ maintains dynamic stability even at ambient pressure and exhibits a high superconducting critical temperature (T_c) of 60 K. At an elevated pressure of 100 GPa, the pressure-stabilized CaYH₈ and CaYH₁₀ structures demonstrate high T_c values of 90 K and 108 K, respectively. With further increased hydrogen content, CaYH₁₂ remains dynamically stable up to 150 GPa and exhibits a remarkable T_c of 225 K. Furthermore, this study discusses how phonon softening in the mid-frequency region, primarily induced by Fermi surface nesting, effectively enhances electron–phonon coupling.