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Fe2N is zeta iron carbide-like structured and crystallizes in the orthorhombic Pbcn space group. The structure is three-dimensional. Fe is bonded in a 3-coordinate geometry to three equivalent N atoms. There are a spread of Fe–N bond distances ranging from 1.87–1.96 Å. N is bonded to six equivalent Fe atoms to form a mixture of edge and corner-sharing NFe6 octahedra. The corner-sharing octahedra tilt angles range from 48–49°.
Fe2N is beta Vanadium nitride structured and crystallizes in the trigonal P-31m space group. The structure is three-dimensional. Fe is bonded in a distorted T-shaped geometry to three N atoms. There is one shorter (1.91 Å) and two longer (1.92 Å) Fe–N bond length. There are two inequivalent N sites. In the first N site, N is bonded to six equivalent Fe atoms to form corner-sharing NFe6 octahedra. The corner-sharing octahedral tilt angles are 48°. In the second N site, N is bonded to six equivalent Fe atoms to form a mixture of edge and corner-sharing NFe6 octahedra. The corner-sharing octahedral tilt angles are 48°.
Fe2N is zeta iron carbide-like structured and crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are twelve inequivalent Fe sites. In the first Fe site, Fe is bonded in a distorted trigonal planar geometry to three N atoms. There are a spread of Fe–N bond distances ranging from 1.87–1.92 Å. In the second Fe site, Fe is bonded in a distorted T-shaped geometry to three N atoms. There are a spread of Fe–N bond distances ranging from 1.87–1.92 Å. In the third Fe site, Fe is bonded in a distorted T-shaped geometry to three N atoms. There are a spread of Fe–N bond distances ranging from 1.91–1.96 Å. In the fourth Fe site, Fe is bonded in a distorted trigonal planar geometry to three N atoms. There is one shorter (1.87 Å) and two longer (1.91 Å) Fe–N bond length. In the fifth Fe site, Fe is bonded in a distorted T-shaped geometry to three N atoms. There are a spread of Fe–N bond distances ranging from 1.87–1.96 Å. In the sixth Fe site, Fe is bonded in a distorted T-shaped geometry to three N atoms. There are a spread of Fe–N bond distances ranging from 1.87–1.96 Å. In the seventh Fe site, Fe is bonded in a distorted T-shaped geometry to three N atoms. There are a spread of Fe–N bond distances ranging from 1.87–1.92 Å. In the eighth Fe site, Fe is bonded in a distorted trigonal planar geometry to three N atoms. There are a spread of Fe–N bond distances ranging from 1.90–1.96 Å. In the ninth Fe site, Fe is bonded in a 3-coordinate geometry to three N atoms. There are a spread of Fe–N bond distances ranging from 1.87–1.96 Å. In the tenth Fe site, Fe is bonded in a 3-coordinate geometry to three N atoms. There are a spread of Fe–N bond distances ranging from 1.87–1.96 Å. In the eleventh Fe site, Fe is bonded in a distorted T-shaped geometry to three N atoms. There are a spread of Fe–N bond distances ranging from 1.90–1.95 Å. In the twelfth Fe site, Fe is bonded in a distorted T-shaped geometry to three N atoms. There are a spread of Fe–N bond distances ranging from 1.91–1.96 Å. There are six inequivalent N sites. In the first N site, N is bonded to six Fe atoms to form a mixture of edge and corner-sharing NFe6 octahedra. The corner-sharing octahedra tilt angles range from 47–50°. In the second N site, N is bonded to six Fe atoms to form a mixture of edge and corner-sharing NFe6 octahedra. The corner-sharing octahedra tilt angles range from 48–50°. In the third N site, N is bonded to six Fe atoms to form a mixture of edge and corner-sharing NFe6 octahedra. The corner-sharing octahedra tilt angles range from 49–50°. In the fourth N site, N is bonded to six Fe atoms to form a mixture of edge and corner-sharing NFe6 octahedra. The corner-sharing octahedra tilt angles range from 47–50°. In the fifth N site, N is bonded to six Fe atoms to form a mixture of edge and corner-sharing NFe6 octahedra. The corner-sharing octahedra tilt angles range from 47–50°. In the sixth N site, N is bonded to six Fe atoms to form a mixture of edge and corner-sharing NFe6 octahedra. The corner-sharing octahedra tilt angles range from 47–50°.
Abstract Nitrogen is an essential element for life, one of the most abundant volatiles in the atmosphere, and an important component in the Earth’s interior, where iron nitride is an essential host of deep nitrogen. Here, we investigate the pressure-induced electronic spin-pairing transition of iron in siderazot (Fe3N1.2) at pressures up to 45.8 GPa at room temperature, using diamond-anvil cell techniques coupled with synchrotron X-ray emission spectroscopy. The integrated intensity of the satellite emission peak (K′β) decreases upon compression but remains unchanged at pressures greater than 30.5 GPa. In other words, the high-spin to low-spin transition of iron in Fe3N1.2 starts immediately at very low pressures and completes at ~30.5 GPa. The iron spin transition completion pressures increase with the nitrogen concentration of hexagonal close-packed iron nitrides (i.e., Fe3N1.2, Fe7N3, and Fe2N). Moreover, the identity and concentration of light elements in binary iron-rich compounds such as Fe3N, Fe3C, Fe3P, Fe3S, Fe7C3, and Fe7N3, together with their crystal structure, could affect the iron spin transition pressures. The spin transition of iron-rich alloys could alter the bonding nature and the physical properties, including the thermal and electrical conductivity, thereby influencing the thermal state and evolution of planetary interiors.