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Thermodynamics of Chemical Processes in the System of Nanocrystalline Iron–Ammonia–Hydrogen at 350 °C. Catalysts 2020. [DOI: 10.3390/catal10111242] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Nanocrystalline iron nitriding and the reduction of nanocrystalline iron nitrides in steady states at 350 °C are described using the chemical potential programmed reaction (CPPR), thermogravimetry (TG), 57Fe Mössbauer spectroscopy (MS), and X-ray diffraction (XRD) methods. It was determined that during the process of nitriding of nanocrystalline iron, larger nanocrystallites formed the γ’ phase and the smallest nanocrystallites (about 4%) were transformed into the α” phase. Both phases were in chemical equilibrium, with the gas phase at the temperature of 350 °C. Stable iron nitride α” was also formed in the ε iron nitride reduction process. Taking the α” phase in the system of nanocrystalline Fe-NH3-H2 into account, it was found that at certain nitriding potentials in the chemical equilibrium state, three solid phases in the nitriding process and four solid phases in the reduction process may coexist. It was also found that the nanocrystallites of ε iron nitride in their reduction process were transformed according to two mechanisms, depending on their size. Larger nanocrystallites of iron nitride ε were transformed into the α-iron phase through iron nitride γ’, and smaller nanocrystallites of ε nitride went through iron nitride α”. In the passivation process of nanocrystalline iron and/or nanocrystalline iron nitrides, amorphous phases of iron oxides and/or iron oxynitrides were formed on their surface.
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Huzan MS, Fix M, Aramini M, Bencok P, Mosselmans JFW, Hayama S, Breitner FA, Gee LB, Titus CJ, Arrio MA, Jesche A, Baker ML. Single-ion magnetism in the extended solid-state: insights from X-ray absorption and emission spectroscopy. Chem Sci 2020; 11:11801-11810. [PMID: 34123206 PMCID: PMC8162461 DOI: 10.1039/d0sc03787g] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Large single-ion magnetic anisotropy is observed in lithium nitride doped with iron. The iron sites are two-coordinate, putting iron doped lithium nitride amongst a growing number of two coordinate transition metal single-ion magnets (SIMs). Uniquely, the relaxation times to magnetisation reversal are over two orders of magnitude longer in iron doped lithium nitride than other 3d-metal SIMs, and comparable with high-performance lanthanide-based SIMs. To understand the origin of these enhanced magnetic properties a detailed characterisation of electronic structure is presented. Access to dopant electronic structure calls for atomic specific techniques, hence a combination of detailed single-crystal X-ray absorption and emission spectroscopies are applied. Together K-edge, L2,3-edge and Kβ X-ray spectroscopies probe local geometry and electronic structure, identifying iron doped lithium nitride to be a prototype, solid-state SIM, clean of stoichiometric vacancies where Fe lattice sites are geometrically equivalent. Extended X-ray absorption fine structure and angular dependent single-crystal X-ray absorption near edge spectroscopy measurements determine FeI dopant ions to be linearly coordinated, occupying a D6h symmetry pocket. The dopant engages in strong 3dπ-bonding, resulting in an exceptionally short Fe–N bond length (1.873(7) Å) and rigorous linearity. It is proposed that this structure protects dopant sites from Renner–Teller vibronic coupling and pseudo Jahn–Teller distortions, enhancing magnetic properties with respect to molecular-based linear complexes. The Fe ligand field is quantified by L2,3-edge XAS from which the energy reduction of 3dz2 due to strong 4s mixing is deduced. Quantification of magnetic anisotropy barriers in low concentration dopant sites is inhibited by many established methods, including far-infrared and neutron scattering. We deduce variable temperature L3-edge XAS can be applied to quantify the J = 7/2 magnetic anisotropy barrier, 34.80 meV (∼280 cm−1), that corresponds with Orbach relaxation via the first excited, MJ = ±5/2 doublet. The results demonstrate that dopant sites within solid-state host lattices could offer a viable alternative to rare-earth bulk magnets and high-performance SIMs, where the host matrix can be tailored to impose high symmetry and control lattice induced relaxation effects. Taking advantage of synchrotron light source methods, we present the geometric and electronic structure of iron doped in lithium nitride.![]()
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Affiliation(s)
- Myron S Huzan
- The University of Manchester at Harwell, Diamond Light Source Harwell Campus OX11 0DE UK .,Department of Chemistry, The University of Manchester Manchester M13 9PL UK
| | - Manuel Fix
- EP VI, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg D-86159 Augsburg Germany
| | - Matteo Aramini
- Diamond Light Source, Harwell Science and Innovation Campus Chilton Didcot OX11 0DE UK
| | - Peter Bencok
- Diamond Light Source, Harwell Science and Innovation Campus Chilton Didcot OX11 0DE UK
| | | | - Shusaku Hayama
- Diamond Light Source, Harwell Science and Innovation Campus Chilton Didcot OX11 0DE UK
| | - Franziska A Breitner
- EP VI, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg D-86159 Augsburg Germany
| | - Leland B Gee
- Department of Chemistry, Stanford University Stanford CA 94305 USA
| | - Charles J Titus
- Department of Physics, Stanford University Stanford CA 94305 USA
| | - Marie-Anne Arrio
- Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, CNRS, Sorbonne Université, IRD, MNHN, UMR7590 75252 Paris Cedex 05 France
| | - Anton Jesche
- EP VI, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg D-86159 Augsburg Germany
| | - Michael L Baker
- The University of Manchester at Harwell, Diamond Light Source Harwell Campus OX11 0DE UK .,Department of Chemistry, The University of Manchester Manchester M13 9PL UK
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Clark WP, Steinberg S, Dronskowski R, McCammon C, Kupenko I, Bykov M, Dubrovinsky L, Akselrud LG, Schwarz U, Niewa R. High-Pressure NiAs-Type Modification of FeN. Angew Chem Int Ed Engl 2017; 56:7302-7306. [PMID: 28517174 PMCID: PMC5488211 DOI: 10.1002/anie.201702440] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2017] [Revised: 04/10/2017] [Indexed: 11/22/2022]
Abstract
The combination of laser-heated diamond anvil cells and synchrotron Mössbauer source spectroscopy were used to investigate high-temperature high-pressure chemical reactions of iron and iron nitride Fe2 N with nitrogen. At pressures between 10 and 45 GPa, significant magnetic hyperfine splitting indicated compound formation after annealing at 1300 K. Subsequent in situ X-ray diffraction reveals a new modification of FeN with NiAs-type crystal structure, as also rationalized by first-principles total-energy and chemical-bonding studies.
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Affiliation(s)
- William P. Clark
- Institut für Anorganische ChemieUniversität StuttgartPfaffenwaldring 5570569StuttgartGermany
| | | | | | | | | | - Maxim Bykov
- Bayerisches GeoinstitutUniversität BayreuthGermany
| | | | - Lev G. Akselrud
- Max-Planck-Institut für Chemische Physik fester Stoffe, DresdenGermany
| | - Ulrich Schwarz
- Max-Planck-Institut für Chemische Physik fester Stoffe, DresdenGermany
| | - Rainer Niewa
- Institut für Anorganische ChemieUniversität StuttgartPfaffenwaldring 5570569StuttgartGermany
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Clark WP, Steinberg S, Dronskowski R, McCammon C, Kupenko I, Bykov M, Dubrovinsky L, Akselrud LG, Schwarz U, Niewa R. Eine NiAs-artige Hochdruckmodifikation von FeN. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201702440] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- William P. Clark
- Institut für Anorganische Chemie; Universität Stuttgart; Pfaffenwaldring 55 70569 Stuttgart Deutschland
| | | | | | | | | | - Maxim Bykov
- Bayerisches Geoinstitut; Universität Bayreuth; Deutschland
| | | | - Lev G. Akselrud
- Max-Planck-Institut für Chemische Physik fester Stoffe; Dresden Deutschland
| | - Ulrich Schwarz
- Max-Planck-Institut für Chemische Physik fester Stoffe; Dresden Deutschland
| | - Rainer Niewa
- Institut für Anorganische Chemie; Universität Stuttgart; Pfaffenwaldring 55 70569 Stuttgart Deutschland
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Jesche A, McCallum RW, Thimmaiah S, Jacobs JL, Taufour V, Kreyssig A, Houk RS, Bud'ko SL, Canfield PC. Giant magnetic anisotropy and tunnelling of the magnetization in Li₂(Li(1-x)Fe(x))N. Nat Commun 2014; 5:3333. [PMID: 24566374 DOI: 10.1038/ncomms4333] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2013] [Accepted: 01/28/2014] [Indexed: 11/09/2022] Open
Abstract
Large magnetic anisotropy and coercivity are key properties of functional magnetic materials and are generally associated with rare earth elements. Here we show an extreme, uniaxial magnetic anisotropy and the emergence of magnetic hysteresis in Li₂(Li(1-x)Fe(x))N. An extrapolated, magnetic anisotropy field of 220 T and a coercivity field of over 11 T at 2 K outperform all known hard ferromagnets and single-molecular magnets. Steps in the hysteresis loops and relaxation phenomena in striking similarity to single-molecular magnets are particularly pronounced for x≪1 and indicate the presence of nanoscale magnetic centres. Quantum tunnelling, in the form of temperature-independent relaxation and coercivity, deviation from Arrhenius behaviour and blocking of the relaxation, dominates the magnetic properties up to 10 K. The simple crystal structure, the availability of large single crystals and the ability to vary the Fe concentration make Li₂(Li(1-x)Fe(x))N an ideal model system to study macroscopic quantum effects at elevated temperatures and also a basis for novel functional magnetic materials.
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Affiliation(s)
- A Jesche
- The Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA
| | - R W McCallum
- 1] The Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA [2] Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011, USA
| | - S Thimmaiah
- The Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA
| | - J L Jacobs
- 1] The Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA [2] Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA
| | - V Taufour
- Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - A Kreyssig
- 1] The Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA [2] Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - R S Houk
- 1] The Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA [2] Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA
| | - S L Bud'ko
- 1] The Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA [2] Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
| | - P C Canfield
- 1] The Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA [2] Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA
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Abstract
Mössbauer spectra of the iron nitrides have been measured at room temperature and at 550°C. In the case of the room temperature spectrum of γ′-Fe4N, a fit strategy is reviewed which accounts for two spectroscopically inequivalent iron Fe(1) sites due to the simultaneous presence of magnetic and quadrupolar interactions. In contrast, the high-temperature spectra of γ′-Fe4N allow for the direct determination of the quadrupolar interactions at Fe(1) sites. In the case of ɛ-Fe3N1+x
, the stoichiometry dependent magnetically-split room temperature spectra demonstrate the extensive ordering of nitrogen in the compound. At 550°C, spectra have been measured at various defined thermodynamic conditions of controlled nitrogen activity. The quadrupole-split spectra high-temperature are discussed in relation to structure and disorder of the material. In particular, it is shown that the composition dependent high-temperature spectra of ɛ-Fe3N1+x
can be modelled in the framework of a simple two-site model.
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