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

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

doi:10.1038/s41598-018-29038-w

Yuanzheng Chen, Hongyan Wang + Show 3 more

Open Access

https://doi.org/10.1038/s41598-018-29038-w

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Journal: Scientific Reports	Publication Date: Jul 13, 2018
Citations: 38	License type: open-access

Affiliation: Southwest Jiaotong University, Jilin University

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 Tc of 4–8 K. This discovery puts the Fe-N system into a new class of desirable materials combining advanced mechanical properties and superconductivity.

Highlights

Nitrogen (N) is the most abundant element in the earth’s atmosphere and is one of the least studied elements regarding the composition of the Earth[1]
In order to systematically explore the possibility of obtaining new stable N-rich iron nitrides, and especially to examine the possibility of attaining new nitrogen species at high pressure (HP), we here present extensive structure searches of stoichiometric Fe-N compounds under various pressures ranging from 0 to 300 GPa, using an unbiased particle swarm optimization (PSO) algorithms for crystal structure predictions[18]
We focused our structure search on the phase stabilities of Fe-N systems in N-rich stoichiometry by calculating the formation enthalpy of various Fe1-i Ni (0 < i < 1) compounds in a pressure range of 0 to 300 GPa

Summary

Introduction

Nitrogen (N) is the most abundant element in the earth’s atmosphere and is one of the least studied elements regarding the composition of the Earth[1]. In order to systematically explore the possibility of obtaining new stable N-rich iron nitrides, and especially to examine the possibility of attaining new nitrogen species at HP, we here present extensive structure searches of stoichiometric Fe-N compounds under various pressures ranging from 0 to 300 GPa, using an unbiased particle swarm optimization (PSO) algorithms for crystal structure predictions[18]. This swarm-intelligence high-throughput searching has proven effective in revealing new compositions favorable to form in large sets of multicomponent Ca-H, Li-B, Xe-N, Cs-N systems[16,17,19,20]. Its structural uniqueness gives rise to a set of remarkable properties for the crystal P63/mcm phase with an unexpectedly Tc of 4~8 K and a good mechanical property

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Results

Conclusion