P-V-T measurements of Fe3C to 117 GPa and 2100 K: Implications for stability of Fe3C phase at core c
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McGuire, Chris↗
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Materials Data on Fe3C by Materials Project
Fe3C is Upper Bainite structured and crystallizes in the hexagonal P6_322 space group. The structure is three-dimensional. Fe is bonded in a bent 120 degrees geometry to two equivalent C atoms. Both Fe–C bond lengths are 1.92 Å. C is bonded to six equivalent Fe atoms to form corner-sharing CFe6 octahedra. The corner-sharing octahedral tilt angles are 52°.
36 MATERIALS SCIENCE↗
Materials Data on Fe3C by Materials Project
Fe3C is Upper Bainite-like structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Fe sites. In the first Fe site, Fe is bonded in a distorted bent 120 degrees geometry to two equivalent C atoms. There is one shorter (1.90 Å) and one longer (1.91 Å) Fe–C bond length. In the second Fe site, Fe is bonded in a distorted bent 120 degrees geometry to two equivalent C atoms. Both Fe–C bond lengths are 1.93 Å. C is bonded to six Fe atoms to form corner-sharing CFe6 octahedra. The corner-sharing octahedra tilt angles range from 48–51°.
36 MATERIALS SCIENCE↗
Materials Data on Fe3C by Materials Project
Computed materials data using density functional theory calculations. These calculations determine the electronic structure of bulk materials by solving approximations to the Schrodinger equation. For more information, see https://materialsproject.org/docs/calculations
36 MATERIALS SCIENCE↗
Materials Data on Fe11MoC4 by Materials Project
MoFe5C2(Fe3C)2 crystallizes in the monoclinic Pm space group. The structure is two-dimensional and consists of one Fe3C sheet oriented in the (0, 1, 0) direction and one MoFe5C2 sheet oriented in the (0, 1, 0) direction. In the Fe3C sheet, there are four inequivalent Fe sites. In the first Fe site, Fe is bonded in a single-bond geometry to one C atom. The Fe–C bond length is 1.79 Å. In the second Fe site, Fe is bonded in a single-bond geometry to one C atom. The Fe–C bond length is 1.88 Å. In the third Fe site, Fe is bonded in a square co-planar geometry to four C atoms. There are two shorter (2.01 Å) and two longer (2.04 Å) Fe–C bond lengths. In the fourth Fe site, Fe is bonded in a square co-planar geometry to four C atoms. There are a spread of Fe–C bond distances ranging from 1.99–2.04 Å. There are two inequivalent C sites. In the first C site, C is bonded to six Fe atoms to form a mixture of corner and edge-sharing CFe6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the second C site, C is bonded to six Fe atoms to form a mixture of corner and edge-sharing CFe6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the MoFe5C2 sheet, Mo is bonded in a square co-planar geometry to four C atoms. There are a spread of Mo–C bond distances ranging from 2.10–2.12 Å. There are three inequivalent Fe sites. In the first Fe site, Fe is bonded in a single-bond geometry to one C atom. The Fe–C bond length is 1.89 Å. In the second Fe site, Fe is bonded in a single-bond geometry to one C atom. The Fe–C bond length is 1.90 Å. In the third Fe site, Fe is bonded in a square co-planar geometry to four C atoms. There are a spread of Fe–C bond distances ranging from 1.92–1.95 Å. There are two inequivalent C sites. In the first C site, C is bonded to two equivalent Mo and four Fe atoms to form a mixture of corner and edge-sharing CFe4Mo2 octahedra. The corner-sharing octahedra tilt angles range from 0–1°. In the second C site, C is bonded to two equivalent Mo and four Fe atoms to form a mixture of corner and edge-sharing CFe4Mo2 octahedra. The corner-sharing octahedra tilt angles range from 0–1°.
36 MATERIALS SCIENCE↗
The iron spin transition of deep nitrogen-bearing mineral Fe3N1.2 at high pressure
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.
Geochemistry & Geophysics↗
Electronic Structure and Spin Correlations in Novel Magnetic Structures
The research has advanced understanding of the interrelation between the crystal structure and magnetism in several materials which are or can be of interest for the development of improved, specialized or more cost-effective permanent magnets, as well as in selected materials for biomedical and catalytic applications. Fundamental aspects of ferromagnetism were investigated for Mn-Ge, Co-V and Co-Ge nanoclusters and for melt-spun Co-Sn alloys. New solution-chemistry synthesis methods were designed and tested for Fe-Pt, Fe3C and Fe3O4 nanoparticles. Off-stoichiometric Laves phases in the Fe-Si-Zr, Fe-Nb and Fe-Ta systems, as well as Fe5(Si,Ge)B2 compounds were assessed as new rare-earth-free permanent magnet materials; all except the Fe-Si-Zr Laves phases were found to be promising enough to merit a further exploration. A new method for manufacturing rare-earth-free magnets based on the MnBi compound was developed; by purposely avoiding oxidation-sensitive fine single-crystalline powders, the new method yields magnets with a 50% larger energy storage capacity. Studies of rare-earth-lean permanent-magnet materials (lean compared to the currently predominant Nd-Fe-B materials) were focused on the tetragonal compound of the ThMn12 structure type and included both discovery and characterization of new formulations and exploration of new fabrication/processing techniques. Among the most significant achievements were successful preparation of a vanadium-lean SmFe11V compound, the first observation of thermomechanically induced texture in nanocrystalline Sm(Fe,V)12 alloys, and a breakthrough reduction-diffusion synthesis of Sm1-xZrx(Fe0.8Co0.2)11.2Ti0.8 single-crystal particles with a coercivity as high as 12.6 kOe. Several experiments aimed at improvement of the Nd-Fe-B magnet have also been undertaken including a five-fold increase of the coercivity through a grain-boundary diffusion treatment of a Nd10Fe84B6 nanocrystalline alloy.
36 MATERIALS SCIENCE↗