First-principles study of high-temperature superconductivity in X₂MH₆ compounds under 20 GPa

Abstract Research on high-temperature superconductors has primarily focused on hydrogen-rich compounds, however, the need for extreme pressures limits their practical applications. The X 2 MH 6 -type structure Mg 2 IrH 6 stands out because it exhibits superconductivity at 160 K under ambient pressure. This study explores ways to enhance the superconducting critical temperature of this structure through atomic substitution and low-pressure treatment. It also evaluates the mechanical, thermodynamic, and dynamic stability of structures formed by replacing Mg and Ir in Mg 2 IrH 6 with elements from the same groups using first-principles calculations. The findings identify eleven stable ternary compounds, four of which exhibit superconducting critical temperatures, with two compounds, Mg 2 RhH 6 and Mg 2 IrH 6 , exceeding 77 K, classifying them as high-temperature superconductors. Their superconducting figures of merit ( S values) are 1.83 and 2.20, respectively, indicating significant potential for practical applications. Theoretical analysis reveals that mid-frequency hydrogen phonons play a crucial role in enhancing superconducting properties through strong electron–phonon coupling interactions. The band structure study highlights the importance of van Hove singularities near the Fermi level. In addition, electron localization function and Fermi surface topology analyses reveal that the Fermi surface shape and density of states are crucial for increasing superconducting critical temperatures.