Exploration of phase stability and low-pressure synthesis of solid nitrogen by means of atomic scake computer simulations and experiments

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A new material - polymeric nitrogen has been recently created from molecular nitrogen under high compression. In this substance each atom is bonded to three nearest neighbors by single covalent bonds. This transformation to a non-molecular phase is of a fundamental interest for understanding the physics of molecular solids and the chemistry of nitrogen. Polymerized nitrogen is a thermodynamically metastable high energy density material (HEDM) that has an energy capacitance about five times higher than any of the known non-nuclear materials. Therefore it is an interesting candidate for an energy storage material. Experimentally, transitions to a non-molecular amorphous nitrogen were reported at low temperatures (about 80 K) for pressures above 180 GPa and crystals with cubic gauche structure were synthesized at high temperatures (T > 2000 K) and pressure above 110 GPa, but up to now none of these phases could be stabilized at atmospheric pressures. In this project we will systematically investigate the pressure-temperature phase stability of polymeric nitrogen and explore possible routes for the polymerization at significantly lower pressures by a combined theoretical and experimental approach. In particular, we will try to recover polymeric nitrogen to atmospheric pressure and search for catalysts that potentially can reduce the pressure of formation of polymeric nitrogen. Atomic scale computer simulations based on density functional theory and molecular dynamics using analytical potentials will guide the experimental search and help to identify thermodynamic and kinetic conditions for phase formation and phase stability.