Zhu Shuangshuang, Peng Feng, Liu Hanyu, Majumdar Arnab, Gao Tao, Yao Yansun
Institute of Atomic and Molecular Physics, Sichuan University , Chengdu 610065, China.
College of Physics and Electronic Information, Luoyang Normal University , Luoyang 471022, China.
Inorg Chem. 2016 Aug 1;55(15):7550-5. doi: 10.1021/acs.inorgchem.6b00948. Epub 2016 Jul 18.
The knowledge of stoichiometries of alkaline-earth metal nitrides, where nitrogen can exist in polynitrogen forms, is of significant interest for understanding nitrogen bonding and its applications in energy storage. For calcium nitrides, there were three known crystalline forms, CaN2, Ca2N, and Ca3N2, at ambient conditions. In the present study, we demonstrated that there are more stable forms of calcium nitrides than what is already known to exist at ambient and high pressures. Using a global structure searching method, we theoretically explored the phase diagram of CaNx and discovered a series of new compounds in this family. In particular, we found a new CaN phase that is thermodynamically stable at ambient conditions, which may be synthesized using CaN2 and Ca2N. Four other stoichiometries, namely, Ca2N3, CaN3, CaN4, and CaN5, were shown to be stable under high pressure. The predicted CaNx compounds contain a rich variety of polynitrogen forms ranging from small molecules (N2, N4, N5, and N6) to extended chains (N∞). Because of the large energy difference between the single and triple nitrogen bonds, dissociation of the CaNx crystals with polynitrogens is expected to be highly exothermic, making them as potential high-energy-density materials.
了解碱土金属氮化物的化学计量比（其中氮可以以多氮形式存在）对于理解氮键及其在能量存储中的应用具有重要意义。对于氮化钙，在环境条件下已知有三种晶体形式，即CaN₂、Ca₂N和Ca₃N₂。在本研究中，我们证明了氮化钙存在比在环境和高压下已知存在的形式更稳定的形式。使用全局结构搜索方法，我们从理论上探索了CaNₓ的相图，并在这个家族中发现了一系列新化合物。特别是，我们发现了一种在环境条件下热力学稳定的新CaN相，它可以使用CaN₂和Ca₂N合成。另外四种化学计量比，即Ca₂N₃、CaN₃、CaN₄和CaN₅，在高压下被证明是稳定的。预测的CaNₓ化合物包含从小分子（N₂、N₄、N₅和N₆）到延伸链（N∞）的各种多氮形式。由于单氮键和三氮键之间的能量差很大，含有多氮的CaNₓ晶体的解离预计会高度放热，使其成为潜在的高能量密度材料。
