A Metastable CaSH${}_3$ Phase Composed of HS Honeycomb Sheets that is Superconducting Under Pressure

Abstract

Evolutionary searches predicted a number of ternary phases that could be synthesized at pressures of 100-300~GPa. $P{6}_3/mmc$ CaSH${}_2$, $Pnma$ CaSH${}_2$, $Cmc{2}_1$ CaSH${}_6$, and $I\bar{4}$ CaSH${}_{20}$ were composed of a Ca-S lattice along with H${}_2$ molecules coordinated in a ``side-on'' fashion to Ca. The H-H bond lengths in these semiconducting phases were elongated because of H${}_2$ $\sigma \to$ Ca d donation, and Ca d$\to$ H${}_2$ ${\sigma }^{\ast }$ back-donation, via a Kubas-like mechanism. $P\bar{6}m2$ CaSH${}_3$, consisting of two-dimensional HS and CaH${}_2$ sheets, was metastable and metallic above \edit{128~GPa}. The presence of van Hove singularities increased its density of states at the Fermi level, and concomitantly the superconducting critical temperature, which was estimated to be as high as \edit{$\sim$100~K at 128~GPa}. This work will inspire the search for superconductivity in materials based upon \edit{honeycomb HX (X=S, Se, Te), and MH${}_2$ (M=Mg, Ca, Sr, Ba) layers} under pressure.

References in corpus (2)

• Superconductive "sodalite"-like clathrate calcium hydride at high pressures
• Superconducting hydrides under pressure

Cited by in corpus (2)

• Structural Diversity and Superconductivity in S-P-H Ternary Hydrides Under Pressure
• The Li-F-H Ternary System at High Pressures