N$_2$H: A Novel Polymeric Hydronitrogen as a High Energy Density Material

TL;DR

This paper reports the discovery of a new polymeric hydronitrogen phase with high energy density and metallic properties, stable above 33 GPa, promising for high energy applications.

Contribution

It introduces a previously unknown N$_2$H polymeric phase discovered via first-principles structure search, with unique structural, electronic, and stability features.

Findings

High energy density (~4.40 KJ/g)

Stable above ~33 GPa pressure

Lattice dynamical stability down to ambient pressure

Abstract

The polymeric phase of nitrogen connected by the lower (than three) order N-N bonds has been long sought after for the potential application as high energy density materials. Here we report a hitherto unknown polymeric N$_2$H phase discovered in the high-pressure hydronitrogen system by first-principle structure search method based on particle swarm optimization algorithm. This polymeric hydronitrogen consists of quasi-one-dimensional infinite armchair-like polymeric N chains, where H atoms bond with two adjacent N located at one side of armchair edge. It is energetically stable against decomposition above ~33 GPa, and shows novel metallic feature as the result of pressure-enhanced charge transfer and delocalization of {\pi} electrons within the infinite nitrogen chains. The high energy density (~4.40 KJ/g), high nitrogen content (96.6%), as well as relatively low stabilization pressure, make it a possible candidate for high energy density applications. It also has lattice dynamical stability down to the ambient pressure, allowing for the possibility of kinetic stability with respect to variations of external conditions. Experimental synthesis of this novel phase is called for.