Prediction of High-Temperature Superconductivity in Cubic Ternary Hydride <i>M</i>₃<i>X</i>H₈ at Ambient Pressure

We present a systematic first-principles study of cubic M3XH8 compounds, where M = Li, Na, Mg, Al, K, Ca, Ga, Rb, Sr, and In and X represents 3d, 4d, and 5d transition metals. Our high-throughput computational screening at ambient pressure, we identify 29 dynamically stable compounds out of the 390 possible combinations. Among these, Mg3OsH8, Ca3FeH8, Al3NbH8, and Al3ScH8 attract our attention. Particularly, Mg3OsH8 is predicted to have remarkably high superconducting transition temperatures (Tc) of ∼73 K at ambient pressure. Our analysis reveals intricate relationships between crystal symmetry, electronic band structure, and superconductivity in this hydrogen-based system. We explore the role of hydrogen in mediating strong electron–phonon coupling and its impact on the superconducting properties. Furthermore, we investigate the potential Fermi surface features in the electronic structure and their correlation with superconductivity. The possible experimental synthesizability of the compounds is demonstrated by comparing their decomposition enthalpies. This work raises the prediction of ternary superconducting hydride templates, highlighting promising high-Tc compounds of the M3XH8 architecture at ambient pressure.