Ternary inorganic compounds containing carbon, nitrogen, and oxygen at high pressures

TL;DR

This study uses first principles calculations to explore high-pressure chemistry of ternary C_{x}N_{y}O_{z} compounds, discovering new stable and metastable materials with potential high energy density and ultrahard properties.

Contribution

It systematically constructs the ternary phase diagram of C_{x}N_{y}O_{z} compounds from 0 to 100 GPa, revealing novel stable and metastable structures including C_{2}N_{2}O and polymorphs of C_{2}NO_{2} and C_{3}N_{2}O_{3}.

Findings

C_{2}N_{2}O is stable above 10 GPa.

Several metastable compounds are energetically favorable.

Predicted compounds have characteristic Raman spectra and equations of state.

Abstract

Ternary C_{x}N_{y}O_{z} compounds are actively researched as novel high energy density and ultrahard materials. Although some synthesis work has been performed at ambient conditions, very little is known about the high pressure chemistry of of C_{x}N_{y}O_{z} compounds. In this work, first principles variable-composition evolutionary structure prediction calculations are performed with the goal of discovering novel mixed C_{x}N_{y}O_{z} materials at ambient and high pressure conditions. By systematically searching ternary variable composition crystalline materials, the full ternary phase diagram is constructed in the range of pressures from 0 to 100 GPa. The search finds the C_{2}N_{2}O crystal containing extended covalent network of C, N, and O atoms, having space group symmetry Cmc2_{1}, and stable above just 10 GPa. Several other novel metastable (CO)_{x}-(N)_{y} crystalline compounds discovered during the search, including two polymorphs of C_{2}NO_{2} and two polymorphs of C_{3}N_{2}O_{3} crystals are found to be energetically favorable compared to polymeric carbon monoxide (CO) and nitrogen. Predicted new compounds are characterized by their Raman spectra and equations of state.