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 -3 m YH 6 and Im -3 m CaH 6 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 -3 m (Y, Ca)H 6 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 -3 m (Y, Ca)H 6 remains highly stable (Δ T c ≤ 1 K) during decompression between 148 and 165 GPa, significantly outperforming binary Im -3 m CaH 6 and Im -3 m YH 6 . 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.