Robust superconducting stability of ternary hydride Im-3m (Y, Ca)H₆ upon decompression

Ternary hydrides, with their superior chemical and structural flexibility over binary systems, open up new avenues for advancing high-performance superconductor research. The Y-Ca-H system is a promising candidate for high-temperature superconductors, as both Im-3m YH₆ and Im-3m CaH₆ exhibit similar structure and excellent superconducting properties, while Y and Ca atoms possess close atomic radii and electronegativities. Here, we report the successful synthesis of Im-3m (Y, Ca)H₆ achieving a maximum superconducting transition temperature (Tc) approximately 224 K at 155 GPa through five independent hightemperature and high-pressure experiments. Remarkably, the T_c of Im-3m (Y, Ca)H₆ remains highly stable (ΔT_c ≤ 1 K) during decompression between 148 and 165 GPa, significantly outperforming binary Im-3m CaH₆ and Im-3m YH₆. The enhanced superconducting properties may stem from the cooperative chemical template effect of Y and Ca atoms near the s-d border, which significantly reinforces H lattice stability and thus maintains superior superconductivity. This study highlights the potential of multicomponent cooperative effects in designing hydride superconductors, offering new insights for achieving high-T_c hydrides at lower pressures in the future.