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 (T_c) 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 T_c 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 T_c of 112 K at 215 GPa, which is the record T_c among A15-type superconductors. Compared to the binary Pm-3n Lu₄H₂₃, the Pm-3n (Lu, Y)₄H₂₃ exhibits a 60% increase in T_c and a 61% enhancement in the upper critical field μ₀H_c2(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 T_c 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.