高能量密度的硅氮/硅碳氮化合物结构与性质的理论研究

Energy source is the driving force and source of national economic development. Research and development of high energy density and environmentally friendly new energy source have always been the goal of scientific community. Nitrogen-rich high energy density materials become one of the most important materials. This is because that energy can be released during the transformation from the polymeric nitrogen to the molecular nitrogen. It is shown that the pressure is one of effective ways to achieve this transformation. In comparison with elemental nitrogen solid, the synthesis pressure of polymeric nitrogen was substantially reduced through the introduction of foreign atoms. Therefore, people have been trying to find suitable elements reacting with nitrogen at lower pressures to produce high energy density polymeric nitrogen. In view of the C3N12 having a high energy density of 15.56 kJ/g and the Si having similar properties to C, the Si-N binary or Si-C-N ternary compounds under high pressures are expected to become potential high energy density materials. Using the swarm-intelligence crystal structure prediction combined with the first-principles, we will study the chemical reaction of Si-N or Si-C-N under high pressures, and find the stable compositions, and determine their stable regions. In addition, we will calculate the energy density of stable compositions and compare them with the known high energy density materials, and screen out new materials with high energy density, and provide the theoretical basis for the related experiment investigations. The research results of this project have certain significance for understanding and recognizing the structures and properties of Si-N binary or Si-C-N ternary compounds.

能源是国民经济发展的动力和源泉。研发高能量密度和环境友好的新能源一直是科学界努力的目标。富氮高能密度材料成为备受关注的材料之一，主要是由于聚合氮转化为分子氮过程中释放能量。压力是实现这种转化的有效手段之一；与氮单质相比，引入外来原子极大地降低聚合氮的合成压力。因此，人们一直努力尝试和发现合适的元素与氮在较低的压力下反应得到高能量密度的聚合氮。鉴于C3N12高能量密度（15.56 kJ/g）以及硅与碳具有相似的性质，高压下硅氮二元/硅碳氮三元化合物有望成为潜在的高能密度材料。本项目拟采用基于群智理论的晶体结构预测与第一性原理相结合，研究高压下硅-氮/硅-碳-氮的化学反应，找到稳定的组分，确定其稳定区间。此外，计算稳定组分的能量密度，通过与报道的高能材料对比，筛选出能量密度高的新材料，为相关实验研究提供理论依据。本项目的研究成果对理解和认识硅氮二元/硅碳氮三元化合物的结构和性质有一定意义。

富氮高能密度材料因其能量密度高和环境友好的优势备受人们关注，这主要归因于卸压过程中聚合氮可以转化为分子氮并伴随着释放巨大能量。考虑到使单质氮转化为聚合氮需要在较高的压力下实现，因此人们致力于通过其他元素与氮的混合物在较低压力下合成聚合氮。鉴于高能量密度材料C3N12以及硅具有与碳相同的性质，压缩的硅氮二元/硅碳氮三元化合物有望成为潜在的高能密度材料，我们基于群智结构预测同第一性原理计算方法相结合系统探索了高压下系列化学计量比硅氮/硅碳氮化合物，构建了硅-氮体系的压力组分相图。计算研究发现稳定配比Si3N4在202.1 GPa由立方Fd-3m结构相变成新的单斜P21/m结构，其结构由SiN6和SiN7两种多面体结构单元堆积而成。在较低压力(17.7 GPa)下，计算重现了更富氮的Pa-3 SiN2化合物，其结构由SiN6八面体构成，并且在常压下是亚稳相。化学成键分析表明其结构稳定性主要来自Si-N与N-N共价键的贡献。电子性质研究表明P21/m Si3N4和Pa-3 SiN2在其稳定的压力区间均展现出非金属特征。进一步的研究表明，SiN2的较高的能量密度(1.81 kJ/g)，较低的合成压力(17.7 GPa)，使其成为潜在的高能量密度材料。该研究拓宽了人们对碳族氮化物的结构和性质的认识，为后续相关研究提供了一定的理论基础。在本项目的支持下共发表SCI论文15篇。