| 1. |
- Dahlqvist, Martin, et al.
(författare)
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Complex magnetism in nanolaminated Mn2GaC
- 2014
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We have used first-principles calculations and Heisenberg Monte Carlo simulations to search for the magnetic ground state of Mn2GaC, a recently synthesized magnetic nanolaminate. We have, independent on method, identified a range of low energy collinear as well as non-collinear magnetic configurations, indicating a highly frustrated magnetic material with several nearly degenerate magnetic states. An experimentally obtained magnetization of only 0.29 per Mn atom in Mn2GaC may be explained by canted spins in an antiferromagnetic configuration of ferromagnetically ordered sub-layers with alternating spin orientation, denoted AFM[0001]. Furthermore, low temperature X-ray diffraction show a new basal plane peak appearing upon a magnetic transition, which is consistent with the here predicted change in inter-layer spacing for the AFM[0001] configuration.
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| 2. |
- Dahlqvist, Martin, et al.
(författare)
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Theoretical Prediction and Synthesis of a Family of Atomic Laminate Metal Borides with In-Plane Chemical Ordering
- 2020
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Ingår i: Journal of the American Chemical Society. - : AMER CHEMICAL SOC. - 0002-7863 .- 1520-5126. ; 142:43, s. 18583-18591
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Tidskriftsartikel (refereegranskat)abstract
- All atomically laminated MAB phases (M = transition metal, A = A-group element, and B = boron) exhibit orthorhombic or tetragonal symmetry, with the only exception being hexagonal Ti2InB2. Inspired by the recent discovery of chemically ordered hexagonal carbides, i-MAX phases, we perform an extensive first-principles study to explore chemical ordering upon metal alloying of M2AlB2 (M from groups 3 to 9) in orthorhombic and hexagonal symmetry. Fifteen stable novel phases with in-plane chemical ordering are identified, coined i-MAB, along with 16 disordered stable alloys. The predictions are verified through the powder synthesis of Mo4/3Y2/3 AlB2 and Mo4/3Sc2/3AlB2 of space group R (3) over barm (no. 166), displaying the characteristic in-plane chemical order of Mo and Y/Sc and Kagome ordering of the Al atoms, as evident from X-ray diffraction and electron microscopy. The discovery of i-MAB phases expands the elemental space of these borides with M = Sc, Y, Zr, Hf, and Nb, realizing an increased property tuning potential of these phases as well as their suggested potential twodimensional derivatives.
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| 3. |
- Griseri, Matteo, et al.
(författare)
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Ta-based 413 and 211 MAX phase solid solutions with Hf and Nb
- 2020
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Ingår i: Journal of the European Ceramic Society. - : ELSEVIER SCI LTD. - 0955-2219 .- 1873-619X. ; 40:54, s. 1829-1838
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Tidskriftsartikel (refereegranskat)abstract
- New bulk MAX phase-based ceramics were synthesized in the Ta-Hf-Al-C and Ta-Nb-Al-C systems. Specifically, (Ta1-x,Hf-x)(4)AlC3 and (Ta1-x,Nb-x)(4)AlC3 stoichiometries with x = 0.05, 0.1, 0.15, 0.2, 0.25 were targeted by reactive hot pressing of Ta2H, HfH2, NbH0.89, Al and C powder mixtures at 1550 degrees C in vacuum. The produced ceramics were characterized in terms of phase composition and microstructure by X-ray diffraction, scanning electron microscopy, electron probe microanalysis and scanning transmission electron microscopy. The investigation confirmed the existence of such M-site solid solutions with low solute concentrations, as predicted by first-principles calculations. These calculations also predicted a linear trend in lattice parameter evolution with increasing Hf concentration, in agreement with the experimental results. In order to increase the low phase purity of the produced ceramics, Sn was added to form (Ta1-x,Hf-x)(4)(Al-0.5,Sn-0.5)C-3 and (Ta1-x,Nb-x)(4)(Al-0.5,Sn-0.5)C-3 double solid solutions, thus resulting in a higher content of the 413 MAX phase compounds in the produced ceramics.
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| 4. |
- Halim, Joseph, et al.
(författare)
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Experimental and Theoretical Investigations of Out-of-Plane Ordered Nanolaminate Transition Metal Borides: M4CrSiB2 (M = Mo, W, Nb)
- 2023
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 62:14, s. 5341-5347
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Tidskriftsartikel (refereegranskat)abstract
- We report the synthesis of three out-of-plane chemically ordered quaternary transition metal borides (o-MAB phases) of the chemical formula M4CrSiB2 (M = Mo, W, Nb). The addition of these phases to the recently discovered o-MAB phase Ti4MoSiB2 shows that this is indeed a new family of chemically ordered atomic laminates. Furthermore, our results expand the attainable chemistry of the traditional M5SiB2 MAB phases to also include Cr. The crystal structure and chemical ordering of the produced materials were investigated using high-resolution scanning transmission electron microscopy and X-ray diffraction by applying Rietveld refinement. Additionally, calculations based on density functional theory were performed to investigate the Cr preference for occupying the minority 4c Wyckoff site, thereby inducing chemical order.
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| 5. |
- Ingason, Arni Sigurdur, et al.
(författare)
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Magnetic Self-Organized Atomic Laminate from First Principles and Thin Film Synthesis
- 2013
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 110
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Tidskriftsartikel (refereegranskat)abstract
- he first experimental realization of a magnetic Mn+1AXn (MAX) phase, (Cr0.75Mn0.25)2GeC, is presented, synthesized as a heteroepitaxial single crystal thin film, exhibiting excellent structural quality. This self-organized atomic laminate is based on the well-known Cr2GeC, with Mn, a new element in MAX phase research, substituting Cr. The compound was predicted using first-principles calculations, from which a variety of magnetic behavior is envisaged, depending on the Mn concentration and Cr/Mn atomic configuration within the sublattice. The analyzed thin films display a magnetic signal at room temperature.
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| 6. |
- Meshkian, Rahele, et al.
(författare)
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Theoretical Analysis, Synthesis, and Characterization of 2D W1.33C (MXene) with Ordered Vacancies
- 2019
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Ingår i: ACS APPLIED NANO MATERIALS. - : AMER CHEMICAL SOC. - 2574-0970. ; 2:10, s. 6209-6219
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis of delaminated 2D W1.33C (MXene) has been performed by selectively etching Al as well as Sc/Y from the recently discovered nanolaminated i-MAX phases (W2/3Sc1/3)(2)AlC and (W2/3Y1/3)(2)AlC. Both quaternary phases produce MXenes with similar flake morphology and with a skeletal structure due to formation of ordered vacancies. The measured O, OH, and F terminations, however, differ in amount as well as in relative ratios, depending on parent material, evident from X-ray photoelectron spectroscopy. These findings are correlated to theoretical simulations based on first-principles, investigating the W1.33C, and the effect of termination configurations on structure, formation energy, stability, and electronic structure. The theoretical results indicate a favored F-rich surface composition, though with a system going from insulating/semiconducting to metallic for different termination configurations, suggesting a high tuning potential of these materials. Additionally, free-standing W1.33C films of 2-4 mu m thickness and with up to 10 wt % polymer (PEDOT:PSS) were tested as electrodes in supercapacitors, showing capacitances up to 600 F cm(-3) in 1 M H2SO4 and high capacitance retention for at least 10000 cycles at 10 A g(-1). This is highly promising results compared to other W-based materials to date.
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| 7. |
- Meshkian, Rahele, et al.
(författare)
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W-Based Atomic Laminates and Their 2D Derivative W1.33C MXene with Vacancy Ordering
- 2018
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 30:21
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Tidskriftsartikel (refereegranskat)abstract
- Structural design on the atomic level can provide novel chemistries of hybrid MAX phases and their MXenes. Herein, density functional theory is used to predict phase stability of quaternary i-MAX phases with in-plane chemical order and a general chemistry (W 2/3 M 2 1/3 ) 2 AC, where M 2 = Sc, Y (W), and A = Al, Si, Ga, Ge, In, and Sn. Of over 18 compositions probed, only two—with a monoclinic C2/c structure—are predicted to be stable: (W 2/3 Sc 1/3 ) 2 AlC and (W 2/3 Y 1/3 ) 2 AlC and indeed found to exist. Selectively etching the Al and Sc/Y atoms from these 3D laminates results in W 1.33 C-based MXene sheets with ordered metal divacancies. Using electrochemical experiments, this MXene is shown to be a new, promising catalyst for the hydrogen evolution reaction. The addition of yet one more element, W, to the stable of M elements known to form MAX phases, and the synthesis of a pure W-based MXene establishes that the etching of i-MAX phases is a fruitful path for creating new MXene chemistries that has hitherto been not possible, a fact that perforce increases the potential of tuning MXene properties for myriad applications.
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| 8. |
- Mockute, Aurelija, et al.
(författare)
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Nanolaminated (Cr,Mn)2AlC alloys by magnetron sputtering and ab initio calculations
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We present an ab initio theoretical analysis of the temperature-dependent stability of hexagonal inherently nanolaminated (Cr1-xMnx)2AlC. The results indicate energetic stability over the composition range x = 0.0 to 0.5 for temperatures 600 to 900 K. Corresponding alloy thin films were grown by magnetron sputtering from four elemental targets. X-ray diffraction in combination with analytical transmission electron microscopy including electron energy-loss spectroscopy and energy dispersive X-ray spectroscopy analysis revealed that the films were epitaxial (0001)-oriented single crystals with x up to 0.16.
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| 9. |
- Mockuté, Aurelija, et al.
(författare)
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Oxygen incorporation in Ti2AlC thin films studied by electron energy loss spectroscopy and ab initio calculations
- 2013
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Ingår i: Journal of Materials Science. - : Springer Verlag (Germany). - 0022-2461 .- 1573-4803. ; 48:10, s. 3686-3691
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Tidskriftsartikel (refereegranskat)abstract
- Substitution of C with O in hexagonal inherently nanolaminated Ti2AlC has been studied experimentally and theoretically. Ti2Al(C1−x O x ) thin films with x ≤ 0.52 are synthesized by both cathodic arc deposition with the uptake of residual gas O, and solid-state reaction between understoichiometric TiC y and Al2O3(0001) substrates. The compositional analysis is made by analytical transmission electron microscopy, including electron energy loss spectroscopy. Furthermore, predictive ab initio calculations are performed to evaluate the influence of substitutional O on the shear stress at different strains for slip on the (0001) basal plane in the [−1010] and [1−210] directions.
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| 10. |
- Mockuté, Aurelija, et al.
(författare)
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Synthesis and ab initio calculations of nanolaminated (Cr,Mn)2AlC compounds
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 87:9
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Tidskriftsartikel (refereegranskat)abstract
- We present an ab initio theoretical analysis of the temperature-dependent stability of inherently nanolaminated (Cr1−xMnx)2AlC. The results indicate energetic stability over the composition range x = 0.0 to 0.5 for temperatures ≥600 K. Corresponding thin film compounds were grown by magnetron sputtering from four elemental targets. X-ray diffraction in combination with analytical transmission electron microscopy, including electron energy-loss spectroscopy and energy dispersive x-ray spectroscopy analysis, revealed that the films were epitaxial (0001)-oriented single-crystals with x up to 0.16.
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