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.高温超导体（high-temperature superconductors）的发现仍是材料科学领域的核心挑战。富氢化合物是最具潜力的候选体系之一，其可在较高临界转变温度（critical temperature, Tc）下表现出声子介导超导电性（phonon-mediated superconductivity），但这类材料的稳定合成通常需要极端高压条件。本研究通过对三元A15型氢化物（ternary A15-type hydrides）开展多阶段高通量筛选（high-throughput screening），并结合由瞬时数据衍生势函数（ephemeral data derived potentials）加速的Y-Sb-H体系高通量计算搜索，鉴定出YSbH6为极具潜力的超导体候选材料。具有Pm-3空间群的立方相YSbH6在50GPa下的预测临界转变温度可达118K，为该压力下迄今已报道的A15型氢化物的最高临界转变温度之一。热力学分析结果显示，YSbH6在50GPa下较能量凸包（convex hull）高出约100meV/原子，而在120GPa下仅高出26meV/原子，表明其在类似高压条件下具备亚稳性（metastability）与合成可行性。该相在20~120GPa的宽压力区间内均具备晶格动力学稳定性，在50GPa下展现出反应动力学稳定性，在20与50GPa下具备弹性稳定性——上述特性均是实现中等压力下长寿命亚稳行为的核心要素。本研究结果将YSbH6确立为一款基准体系，用以阐明三元氢化物中高临界转变温度性能与有限热力学稳定性之间的平衡关系，同时凸显了整合晶格动力学、热力学、动力学与弹性稳定性分析对于指导亚稳超导体实验合成的重要意义。