Journal
JOURNAL OF ALLOYS AND COMPOUNDS
Volume 702, Issue -, Pages 132-137Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.jallcom.2017.01.219
Keywords
Iron-nitrides compounds; Dinitrogen; High pressure; Particle swarm optimization
Categories
Funding
- Southwest jiaotong University [A0920502051509-35]
- China National Science Foundation [11604270, 11174237, 11404268, 21363013]
- Sichuan Province, Applied Science and Technology Project [2013JY0035]
- Fundamental Research Funds for the Central Universities [2682014ZT30, 2682015QM04]
- Computational Physics Key Laboratory of Sichuan Province, Yibin University [2016H01038]
- state key laboratory cultivation base construction, Inner Mongolia University of Science Technology [2015H01424]
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Using the unbiased structure searching CALYPSO techniques and the first-principles calculations, we predicted a phase transition in iron pernitride (FeN2) at 22 GPa from the hexagonal R-3m structure to an orthorhombic Pnnm structure. Although the Pnnm structure is a well-known marcasite phase of transition-metal pernitrides, to our knowledge, this is the first report about the pressure-induced phase transition to the Pnnm structure in the FeN2 compound. The dynamically and mechanically stable for the Pnnm phase are evaluated, further confirming this phase transition. By assessing the elastic property of the Pnnm structure, the result indicates that it displays excellent brittle and hardness characters. Viewing it's structure, a dinitrogen unit and a coordinating iron atom characterized by N-sharing six-fold FeN6 octahedrons are found. Based on the quantum-chemical analysis, the dinitrogen unit was formulated as a quasi-molecular double-bonded NZ and a mixed covalent N N and Fe N bonding nature was identified in the structure. These structural and covalent bonding characters play a crucial role to its excellent mechanical properties. The present results extend the well-known marcasite phase in other transition metal pernitrides to the FeN2 compound and provide a perspective toward the understanding of the synthesis and chemical bonding of N-rich FeN2 under high pressure. (C) 2017 Elsevier B.V. All rights reserved.
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