Stability of xenon-sodium compounds at moderately low pressures

TL;DR

This study predicts and characterizes stable xenon-sodium compounds at pressures below 100 GPa, revealing novel structures and metallic properties, expanding understanding of inert gas reactivity under pressure.

Contribution

First ab initio prediction of stable Xe-Na compounds at moderate pressures, identifying new structures including a cation-vacant CaIrO3-type compound.

Findings

NaXe, NaXe3, and NaXe4 are stable and metallic.

NaXe has a cubic CsCl structure.

NaXe3 has a unique structure similar to post-perovskite.

Abstract

A growing body of theoretical and experimental evidence suggests that inert gases (He, Ne, Ar, Kr, Xe, Rn) become less and less inert under increasing pressure. Here we use the ab initio evolutionary algorithm to predict stable compounds of Xe and Na at pressures below 100 GPa, and find three stable compounds, NaXe, NaXe$_3$ and NaXe$_4$. The NaXe belongs to a well-known cubic CsCl structure type. The NaXe$_4$'s structure is common in amphiboles, whereas the NaXe$_3$ has a unique structure, analogous to the "post-perovskite" orthorhombic CaIrO$_3$-type structure with Ir atoms removed. This is the first time that a cation-vacant version of the CaIrO$_3$ is found in any compound. NaXe, NaXe$_3$ and NaXe$_4$ are found to be metallic.