Prediction and characterization of the marcasite phase of iron pernitride under high pressure

Abstract

Using the unbiased structure searching CALYPSO techniques and the first-principles calculations, we predicted a phase transition in iron pernitride (FeN 2) 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 FeN 2 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 FeN 6 octahedrons are found. Based on the quantum-chemical analysis, the dinitrogen unit was formulated as a quasi-molecular double-bonded N 2 2and 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 FeN 2 compound and provide a perspective toward the understanding of the synthesis and chemical bonding of N-rich FeN 2 under high pressure.

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

“…In the FeN 2 compound, the low pressure crystalline phase is a trigonal R -3 m structure at approximately 22 GPa, above which an orthorhombic Pnnm structure becomes more favorable, consistent with the previous reports 11 , 12 . These two structures both contain a dinitrogen unit and N-sharing six-fold FeN 6 octahedrons (Figs S11 , 12 ).…”

“…However, in contrast to the Fe-rich compounds, there is little work on the N-rich iron nitrides, both from the experimental and theoretical sides. Only few theoretical investigations are available to report that an N-rich iron pernitride (FeN 2 ) crystallizes in the space group R -3 m at 17 GPa (1000 K) 11 and transforms an orthorhombic Pnnm structure up to 22 GPa 12 obtained by assuming the parent metal under pressure. All these known Fe–N compounds adapt single N atom or molecule N 2 configuration and keep iron 6-coordination.…”

The Structure of Ferroselite, FeSe2, at Pressures up to 46 GPa and Temperatures down to 50 K: A Single-Crystal Micro-Diffraction Analysis

“…Upon attempting to maintain a constant pressure in the sample chamber during further cooling by increasing the gas membrane pressure, the experiment failed abruptly when the load on the DAC applied with the gas membrane was rapidly transferred to the diamond anvils upon overcoming the DAC friction. (6) 0.3695 (7) We expected the effect on structural parameters of lowering temperature from 300 to 50 K to be small, close to the resolution of our experiment. Hence we loaded three crystals with different orientations for this experiment in order to obtain a more complete sampling of the reciprocal space and increase data redundancy.…”

“…Compounds with the marcasite crystal structure display a variety of intriguing physical properties intimately related to their structural arrangements [4]. Furthermore, the marcasite structure type is adopted by several interesting high-pressure phases such as Fe, Rh and Os pernitrides [5][6][7].…”

The Structure of Ferroselite, FeSe₂, at Pressures Upto 46 GPa and Temperatures Down to 50 K: ASingle-Crystal Micro-Diffraction Analysis

“…Compounds with the marcasite crystal structure display a variety of intriguing physical properties intimately related to their structural arrangements [4]. Furthermore, the marcasite structure type is adopted by a number of interesting high-pressure phases such as Fe, Rh and Os pernitrides [5], [6], [7].…”