Novel triadius-like N4 specie of iron nitride compounds under high pressure

Yuanzheng Chen; Xinyong Cai; Hongyan Wang; Hongbo Wang; Hui Wang

doi:10.1038/s41598-018-29038-w

Novel triadius-like N₄ specie of iron nitride compounds under high pressure

Sci Rep. 2018 Jul 13;8(1):10670. doi: 10.1038/s41598-018-29038-w.

Authors

Yuanzheng Chen¹, Xinyong Cai², Hongyan Wang², Hongbo Wang³, Hui Wang⁴

Affiliations

¹ School of Physical Science and Technology, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu, 610031, China. cyz@calypso.org.cn.
² School of Physical Science and Technology, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Southwest Jiaotong University, Chengdu, 610031, China.
³ State Key Lab of Superhard Materials, Jilin University, Changchun, 130012, China. cyz@home.swjtu.edu.cn.
⁴ State Key Lab of Superhard Materials, Jilin University, Changchun, 130012, China.

Abstract

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 (N₂). 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 FeN₂ stabilizes by a break up of molecule N₂ into a novel planar N₄ unit (P6₃/mcm, >228 GPa) while FeN₄ stabilizes by a infinite 1D linear nitrogen chains N∞ (P-1, >50 GPa; Cmmm, >250 GPa). In the intriguing N₄ specie of P6₃/mcm-FeN₂, 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_c of 4-8 K. This discovery puts the Fe-N system into a new class of desirable materials combining advanced mechanical properties and superconductivity.