Chen Yuanzheng, Cai Xinyong, Wang Hongyan, Wang Hongbo, Wang Hui
School of Physical Science and Technology, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu, 610031, China.
State Key Lab of Superhard Materials, Jilin University, Changchun, 130012, China.
Sci Rep. 2018 Jul 13;8(1):10670. doi: 10.1038/s41598-018-29038-w.
Various nitrogen species in nitrides are fascinating since they often appear with these nitride as superconductors, hard materials, and high-energy density. As a typical complex, though iron nitride has been intensively studied, nitrogen species in the iron-nitrogen (Fe-N) compounds only have been confined to single atom (N) or molecule nitrogen (N). Using a structure search method based on the CALYPSO methodology, unexpectedly, we here revealed two new stable high pressure (HP) states at 1:2 and 1:4 compositions with striking nitrogen species. The results show that the proposed FeN stabilizes by a break up of molecule N into a novel planar N unit (P6/mcm, >228 GPa) while FeN stabilizes by a infinite 1D linear nitrogen chains N∞ (P-1, >50 GPa; Cmmm, >250 GPa). In the intriguing N specie of P6/mcm-FeN, we find that it possesses three equal N = N covalent bonds and forms a perfect triadius-like configuration being never reported before. This uniqueness gives rise to a set of remarkable properties for the crystal phase: it is identified to have a good mechanical property and a potential for phonon-mediated superconductivity with a T of 4-8 K. This discovery puts the Fe-N system into a new class of desirable materials combining advanced mechanical properties and superconductivity.
氮化物中的各种氮物种很吸引人，因为它们常作为超导体、硬质材料和高能量密度材料与这些氮化物一起出现。作为一种典型的复合物，尽管氮化铁已得到深入研究，但铁氮（Fe-N）化合物中的氮物种仅局限于单个原子（N）或分子氮（N₂）。使用基于CALYPSO方法的结构搜索方法，出乎意料的是，我们在此揭示了在1:2和1:4组成下具有显著氮物种的两种新的稳定高压（HP）状态。结果表明，所提出的FeN₂通过将分子氮分解为一种新型平面N单元（P6/mcm，>228 GPa）而稳定，而FeN₄通过无限的一维线性氮链N∞（P-1，>50 GPa；Cmmm，>250 GPa）而稳定。在引人入胜的P6/mcm-FeN₂的氮物种中，我们发现它具有三个相等的N=N共价键，并形成了一种前所未有的完美三半径状构型。这种独特性赋予了该晶相一系列显著特性：它被确定具有良好的机械性能以及在4 - 8 K的温度下具有声子介导超导性的潜力。这一发现将Fe-N体系带入了一类兼具先进机械性能和超导性的理想材料中。
