Modeling of the pressure induced formation of a random network of a mixture of N2 and CO crystals

First principles calculations were performed to understand pressure induced transition to extended solid of substitutional mixtures of N2 and CO in crystalline delta phase. The transition occurs at ∼7-9 GPa and has a hysteresis allowing to stabilize covalently bonded random network down to much lower pressures. Only two atoms of N out of 24 were found to be incorporated in random network formed mainly by C and O atoms in 128 atom unit cell. Here, in search of a new route for the synthesis of poly-nitrogen materials, higher concentrations of N atoms (37.5%, 50%, and 90.625%) in delta molecular crystal phases under compression up to 50 GPa were calculated using density functional theory. Presence of CO is found to facilitate formation of the random network. To understand the importance of initial molecular crystalline structure the calculations were performed for the mixtures of N2 and CO in delta phases and at different sites with spherical and disk shaped disorder. Results calculated in linear response th...