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.
@article{arxiv.1506.08362,
title = {Nitrogen oxides under pressure stability, ionization, polymerization, and superconductivity},
author = {Dongxu Li and Artem R. Oganov and Xiao Dong and Xiang-Feng Zhou and Qiang Zhu and Guangrui Qian and Huafeng Dong},
journal= {arXiv preprint arXiv:1506.08362},
year = {2015}
}