Synthesis and Superconductivity of Ternary A15-(Lu, Y)4H23 at High Pressures

Ternary hydrides, formed by introducing new elements into binary hydrides, are a crucial pathway for enhancing superconducting transition temperatures (Tc) or reducing the stable pressures. In this work, we have acquired the ternary hydride formed by Lu and Y atoms, inspired by the low stabilization pressure of the Lu–H system with its fully filled 4f electrons, as well as the higher Tc of the Y–H system. By effectively controlling the high-pressure and high-temperature conditions, we have successfully synthesized Pm-3n (Lu, Y)4H23 (A15-type). The synthesized Pm-3n (Lu, Y)4H23 reveals the highest Tc of 112 K at 215 GPa, which is the record Tc among A15-type superconductors. Compared to the binary Pm-3n Lu4H23, the Pm-3n (Lu, Y)4H23 exhibits a 60% increase in Tc and a 61% enhancement in the upper critical field μ0Hc2(0). Interestingly, Pm-3n (Lu, Y)4H23 displays minimal volume expansion and a slight increase in the H–H bond distance relative to Pm-3n Lu4H23 due to the introduction of Y atoms. Combined theoretical and experimental analyses indicate that the substitution of Lu atoms with Y atoms enhances electron–phonon coupling (EPC) through modified electronic bands and phonon softening caused by the expansion of H–H bonds, collectively driving the significant enhancement of Tc in Pm-3n (Lu, Y)4H23. Our work demonstrates a crucial strategy for adjusting and enhancing the superconducting performance of hydrides and offers valuable practical experience for developing ternary hydrides.