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

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 YSbH6 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-3 YSbH6 phase exhibits a predicted critical temperature of 118K at 50GPa, among the highest Tc reported to date for an A15-hydride at this pressure. Thermodynamic analysis shows that YSbH6 lies ~100meV/atom above the convex hull at 50GPa, but only 26meV/atom above the hull at 120GPa, suggesting possible metastability and synthesis at similar high pressure conditions. The phase is dynamically stable over a wide pressure range (20-120GPa), displays kinetic stability at 50GPa and elastic stability at 20 and 50GPa, key ingredients for long-lived metastable behaviour at moderate pressures. These results highlight YSbH6 as a benchmark case illustrating the balance between high-Tc 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.