Nitrogen oxides under pressure stability, ionization, polymerization, and superconductivity

TL;DR

This study uses ab initio simulations to explore nitrogen oxides under high pressure, revealing phase transformations, stability limits, and superconductivity in certain nitrogen-oxygen compounds.

Contribution

It provides new insights into the high-pressure phases, stability, and superconducting properties of nitrogen oxides, which were previously not well understood.

Findings

NO2 undergoes phase transformations at 7 and 64 GPa

NO becomes superconducting at 198 GPa with Tc = 2.0 K

N2O5 transforms from P-1 to C2/c structure at 51 GPa

Abstract

Nitrogen oxides are textbook class of molecular compounds, with extensive industrial applications. Nitrogen and oxygen are also among the most abundant elements in the universe. We explore the N-O system at 0 K and up to 500 GPa though ab initio evolutionary simulations. Results show that two phase transformations of stable molecular NO2 exist at 7 and 64 GPa, and followed by decomposition of NO2 at 91 GPa. All of the NO+NO3- structures are found to be metastable at T=0 K, so experimentally reported ionic NO+NO3- is either metastable or stabilized by temperature. Upon increasing pressure, N2O5 transforms from P-1 to C2/c structure at 51 GPa. NO becomes thermodynamically stable at 198 GPa. This polymeric phase is superconducting (Tc = 2.0 K) and contains a -N-N- backbone.