First-principles study of high-temperature superconductivity in ScXH8 (X = Y, La, Zr, Mg, Ca, Hf) compounds under high pressure

High-pressure hydrogen-rich compounds have attracted great interest because of their theoretical potential for achieving high-temperature superconductivity. In this study, ScH 4 with an I 4/ mmm structure was used as a fundamental model to construct a series of ternary hydrides, ScXH 8 , by introducing a second metal element (X) through substitution. First-principles calculations were performed to systematically examine how different substitutions affect the superconducting properties of these compounds. The results show that introducing Y, La, Zr, Mg, Ca, and Hf leads to the formation of thermodynamically and dynamically stable compounds within specific pressure ranges, all exhibiting superconducting behavior. Among them, ScMgH 8 exhibits the highest predicted superconducting critical temperature, reaching a critical temperature ( T c ) of 150.7 K at 200 GPa, while ScYH 8 achieves a T c of 130.8 K at 190 GPa. Theoretical analysis shows that strong electron-phonon coupling related to mid- to high-frequency hydrogen phonons is the key factor in enhancing T c , and this is the dominant factor governing the superconducting performance. Electronic states near the Fermi level that are mainly contributed by hydrogen and have a relatively large total density of states further strengthen this coupling. In addition, a more complex and connected Fermi surface can provide more effective scattering channels, thereby further promoting T c .