Helium Induced Nitrogen Salt at High Pressure

Abstract

The energy landscape of helium-nitrogen mixtures is explored by ab initio evolutionary searches, which predicted several stable helium-nitrogen compounds in the pressure range from 25 to 100 GPa. In particular, the monoclinic structure of HeN${}_{22}$ consists of neutral He atoms, partially ionic dimers N${}_2$${}^{\delta -}$, and lantern-like cages N${}_{20}$${}^{\delta +}$. The presence of helium not only greatly enhances structural diversity of nitrogen solids, but also tremendously lowers the formation pressure of nitrogen salt. The unique nitrogen framework of (HeN${}_{20}$)${}^{\delta +}$N${}_2$${}^{\delta -}$ may be quenchable to ambient pressure even after removing helium. The estimated energy density of N${}_{20}$${}^{\delta +}$N${}_2$${}^{\delta -}$ (10.44 kJ/g) is $\sim$2.4 times larger than that of trinitrotoluene (TNT), indicating a very promising high-energy-density material.

arXiv comment6 pages, 4 figures

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• Helium-bearing superconductor at high pressure