A systematic study on the phase diagram and superconductivity of ternary clathrate Y–Mg–H under high pressures

This study investigates promising candidates for high T${}_c$ superconductors within hydrogen-dominated compounds. Through integration of swarm-intelligence structural searches with DFT simulations, we systematically examined phase stability and superconducting properties in the Y–Mg–H ternary system across high-pressure regimes (100–250 GPa). For the predicted candidate structures of Y–Mg–H systems, to investigate the bonding behavior of stable phases, we examined the pressure-induced phase diagrams and thermodynamic convex hulls across a broad range of compositions, and also conducting a detailed analysis of the electronic structure of all predicted phases. To evaluate the superconductivity, we conducted systematic phonon spectrum calculations on the predicted stable structures to assess their T${}_c$. Our analysis reveals that hydrogen-derived states predominantly govern the E${}_F$ electronic structure, serving as a critical determinant for elevated T${}_c$. Electron–phonon interaction analysis further demonstrates hydrogen-dominated lattice vibrations significantly boost the coupling strength, thereby establishing fundamental phonon-mediated mechanisms for high-T${}_c$ realization. Combined with the obtained $\lambda$, we calculated the T${}_c$ of these compounds using the Allen–Dynes modified McMillan equation. The results indicate that $P\bar{3}m1$-Y${}_2$MgH${}_{18}$ has the highest estimated T${}_c$ of 235 K at 140 GPa (with $\mu$ = 0.1), followed by $R\bar{3}m$-YMg${}_3$H${}_{24}$ (224 K at 140 GPa), $P\bar{3}m1$-YMg${}_2$H${}_{18}$ (213 K at 140 GPa), and $Fd\bar{3}m$-YMgH${}_{12}$ at a higher pressure of 190 GPa (220 K). These findings demonstrate that by optimizing the structure of the Y–Mg–H system, it is possible to achieve higher T${}_c$ at relatively lower pressures (e.g., below 200 GPa), providing new directions and ideas for the research of high-temperature superconducting materials.