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

以分子氮为原料，在高压缩条件下制备了一种新材料——聚合氮。在这种物质中，每个原子通过单个共价键与最近的三个原子相连。这种向非分子相的转变对于理解分子固体的物理性质和氮的化学性质具有重要意义。聚合氮是一种热力学亚稳的高能量密度材料（HEDM），其能量电容比任何已知的非核材料高约5倍。因此，它是一种有趣的储能材料。实验报道了在180 GPa以上的低温（约80 K）条件下向非分子无定形氮的转变，在110 GPa以上的高温（约2000 K）条件下合成了具有立方间扭结构的晶体，但到目前为止，这些相都不能在大气压下稳定。在这个项目中，我们将系统地研究聚合氮的压力-温度相稳定性，并通过理论和实验相结合的方法探索在较低压力下聚合的可能途径。特别是，我们将尝试将聚合氮恢复到大气压，并寻找可能降低聚合氮形成压力的催化剂。基于密度泛函理论和使用分析势的分子动力学的原子尺度计算机模拟将指导实验研究，并有助于确定相形成和相稳定性的热力学和动力学条件。

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.