Metastability and high-$T_{\rm c}$ superconductivity in A15-type ternary hydride YSbH$_{6}$ at moderate pressure

Abstract

The discovery of high-temperature superconductors remains a central challenge in materials science. Hydrogen-rich compounds are among the most promising candidates, as they can exhibit phonon-mediated superconductivity at elevated critical temperatures, though their stabilization typically requires extreme pressures. % Here, we report the identification of YSbH${6}$ as a promising superconductor by a multi-stage high-throughput screening on ternary A15-type hydrides, followed by a high-throughput computational search of the Y--Sb--H system, accelerated by ephemeral data derived potentials. % The cubic $Pm\Bar{3}$ YSbH${6}$ phase exhibits a predicted critical temperature of 118,K at 50,GPa, among the highest $T_{\rm c}$ reported to date for an A15-hydride at this pressure. Thermodynamic analysis shows that YSbH${6}$ lies $\sim$100,meV/atom above the convex hull at 50,GPa, but only 26,meV/atom above the hull at 120,GPa, suggesting possible metastability and synthesis at similar high pressure conditions. The phase is dynamically stable over a wide pressure range (20--120,GPa), displays kinetic stability at 50,GPa and elastic stability at 20 and 50,GPa, key ingredients for long-lived metastable behaviour at moderate pressures. % These results highlight YSbH${6}$ as a benchmark case illustrating the balance between high-$T_{\rm c}$ performance and limited thermodynamic stability in ternary hydrides, and underscore the importance of combined dynamic, thermodynamic, kinetic and elastic stability analyses for guiding experimental synthesis of metastable superconductors.