High-pressure Mg-Sc-H phase diagram and its superconductivity from first-principles calculations

Abstract

In this work, global search for crystal structures of ternary Mg-Sc-H hydrides (Mg${}_x$Sc${}_y$H${}_z$) under high pressure ($100\le P\le 200$ GPa) were performed using the evolutionary algorithm and first-principles calculations. Based on them, we computed the thermodynamic convex hull and pressure-dependent phase diagram of Mg${}_x$Sc${}_y$H${}_z$ for $z/(x+y)<4$. We have identified the stable crystal structures of four thermodynamically stable compounds with the higher hydrogen content, i.e., $R\bar{3}m$-MgScH${}_6$, $C2/m$-Mg${}_2$ScH${}_{10}$, $Immm$-MgSc${}_2$H${}_9$ and $Pm\bar{3}m$-Mg(ScH${}_4$)${}_3$. Their superconducting transition temperatures were computationally predicted by the McMillan-Allen-Dynes formula combined with first-principles phonon calculations. They were found to exhibit superconductivity; among them, $R\bar{3}m$-MgScH${}_6$ was predicted to have the highest $T_c$ (i.e. 23.34 K) at 200 GPa.

arXiv comment7 pages, 5 figures, 1 Supplemental Material

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