| 1. |
- Champagne, A., et al.
(författare)
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First-order Raman scattering of rare-earth containing i-MAX single crystals (Mo2/3RE1/3)(2)AlC (RE = Nd, Gd, Dy, Ho, Er)
- 2019
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Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 3:5
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we report on the growth of single crystals of various (Mo2/3RE1/3)(2)AlC (RE = Nd, Gd, Dy, Ho, Er) i-MAX phases and their Raman characterization. Using first principles, the wave numbers of the various phonon modes and their relative atomic displacements are calculated and compared to experimental results. Twelve high-intensity Raman peaks are identified as the fingerprint of this new family of rare-earth containing i-MAX phases, thus being a useful tool to investigate their corresponding composition and structural properties. Indeed, while a redshift is observed in the low-wave-number range due to an increase of the rare-earth atomic mass when moving from left to right on the lanthanide row, a blueshift is observed for most of the high-wave-number modes due to a strengthening of the bonds. A complete classification of bond stiffnesses is achieved based on the direct dependence of a phonon mode wave number with respect to the bond stiffness. Finally, STEM images are used to confirm the crystal structure.
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| 2. |
- Dahlqvist, Martin, et al.
(författare)
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Out-Of-Plane Ordered Laminate Borides and Their 2D Ti-Based Derivative from Chemical Exfoliation
- 2021
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Ingår i: Advanced Materials. - : Wiley-VCH Verlagsgesellschaft. - 0935-9648 .- 1521-4095. ; 33:38
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Tidskriftsartikel (refereegranskat)abstract
- Exploratory theoretical predictions in uncharted structural and compositional space are integral to materials discoveries. Inspired by M5SiB2 (T2) phases, the finding of a family of laminated quaternary metal borides, M M-4 SiB2, with out-of-plane chemical order is reported here. 11 chemically ordered phases as well as 40 solid solutions, introducing four elements previously not observed in these borides are predicted. The predictions are experimentally verified for Ti4MoSiB2, establishing Ti as part of the T2 boride compositional space. Chemical exfoliation of Ti4MoSiB2 and select removal of Si and MoB2 sub-layers is validated by derivation of a 2D material, TiOxCly, of high yield and in the form of delaminated sheets. These sheets have an experimentally determined direct band gap of approximate to 4.1 eV, and display characteristics suitable for supercapacitor applications. The results take the concept of chemical exfoliation beyond currently available 2D materials, and expands the envelope of 3D and 2D candidates, and their applications.
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| 3. |
- Dahlqvist, Martin, et al.
(författare)
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Prediction and synthesis of a family of atomic laminate phases with Kagome-like and in-plane chemical ordering
- 2017
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Ingår i: Science Advances. - : AMER ASSOC ADVANCEMENT SCIENCE. - 2375-2548. ; 3:7
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Tidskriftsartikel (refereegranskat)abstract
- The enigma of MAX phases and their hybrids prevails. We probe transition metal (M) alloying in MAX phases for metal size, electronegativity, and electron configuration, and discover ordering in these MAX hybrids, namely, (V2/3Zr1/3)(2)AlC and (Mo2/3Y1/3)(2)AlC. Predictive theory and verifying materials synthesis, including a judicious choice of alloying M from groups III to VI and periods 4 and 5, indicate a potentially large family of thermodynamically stable phases, with Kagome-like and in-plane chemical ordering, and with incorporation of elements previously not known for MAX phases, including the common Y. We propose the structure to be monoclinic C2/c. As an extension of the work, we suggest a matching set of novel MXenes, from selective etching of the A-element. The demonstrated structural design on simultaneous two-dimensional (2D) and 3D atomic levels expands the property tuning potential of functional materials.
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| 4. |
- 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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| 5. |
- Ding, Haoming, et al.
(författare)
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Progress in Structural Tailoring and Properties of Ternary Layered Ceramics
- 2023
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Ingår i: Journal of Inorganic Materials. - : SCIENCE PRESS. - 1000-324X. ; 38:8, s. 845-884
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Forskningsöversikt (refereegranskat)abstract
- MAX/MAB phases are a series of non-van der Waals ternary layered ceramic materials with a hexagonal structure, rich in elemental composition and crystal structure, and embody physical properties of both ceramics and metals. They exhibit great potential for applications in extreme environments such as high temperature, strong corrosion, and irradiation. In recent years, two-dimensional (2D) materials derived from the MAX/MAB phase (MXene and MBene) have attracted enormous interest in the fields of materials physics and materials chemistry and become a new 2D van der Waals material after graphene and transition metal dichalcogenides. Therefore, structural modulation of MAX/MAB phase materials is essential for understanding the intrinsic properties of this broad class of layered ceramics and for investigating the functional properties of their derived structures. In this paper, we summarize new developments in MAX/MAB phases in recent years in terms of structural modulation, theoretical calculation, and fundamental application research and provide an outlook on the key challenges and prospects for the future development of these layered materials.
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| 6. |
- Hu, C., et al.
(författare)
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Mo2Ga2C: a new ternary nanolaminated carbide
- 2015
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Ingår i: Chemical Communications. - : Royal Society of Chemistry. - 1359-7345 .- 1364-548X. ; 51:30, s. 6560-6563
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Tidskriftsartikel (refereegranskat)abstract
- We report the discovery of a new hexagonal Mo2Ga2C phase, wherein two Ga layers - instead of one - are stacked in a simple hexagonal arrangement in between Mo2C layers. It is reasonable to assume this compound is the first of a larger family.
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| 7. |
- Intikhab, Saad, et al.
(författare)
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Stoichiometry and surface structure dependence of hydrogen evolution reaction activity and stability of MoxC MXenes
- 2019
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Ingår i: Journal of Catalysis. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0021-9517 .- 1090-2694. ; 371, s. 325-332
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Tidskriftsartikel (refereegranskat)abstract
- The exploration of non-precious catalysts for the hydrogen evolution reaction (HER) remains critical in the commercialization of electrochemical energy storage and conversion technologies. Two-dimensional transitional metal carbides called MXenes have been found to have great potential as electrocatalysts for HER. In this work, we synthesize two molybdenum-based MXenes: Mo1.33CTz and Mo2CTz, and measure their HER activity and operational durability. The ordered divacancies on the basal planes of Mo1.33CTz cause a marked decrease in HER activity compared to Mo2CTz. The stoichiometry and atomic surface structure of MXenes is found to be critically important for catalytic activity while having less of an impact on operational durability. This work provides insight for the development of active 2D materials, in general and MXenes in particular for HER and other technologically relevant electrochemical reactions. (C) 2019 Elsevier Inc. All rights reserved.
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| 8. |
- Lai, Chung-Chuan, et al.
(författare)
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Magnetic properties and structural characterization of layered (Cr0.5Mn0.5)(2)AuC synthesized by thermally induced substitutional reaction in (Cr0.5Mn0.5)(2)GaC
- 2018
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Ingår i: APL Materials. - : AMER INST PHYSICS. - 2166-532X. ; 6:2
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic properties of the new phase (Cr0.5Mn0.5)(2)AuC are compared to the known MAX-phase (Cr0.5Mn0.5)(2)GaC, where the former was synthesized by thermally induced substitution reaction of Au for Ga in (Cr0.5Mn0.5)(2)GaC. The reaction introduced a lattice expansion of similar to 3% along the c-axis, an enhancement of the coercive field from 30 mT to 140 mT, and a reduction of the Curie temperature and the saturation magnetization. Still, (Cr0.5Mn0.5)(2)AuC displays similar features in the magnetic field-and temperature-dependent magnetization curves as previously reported magnetic MAX phases, e.g., (Cr0.5Mn0.5)(2)GaC and (Mo0.5Mn0.5)(2)GaC. Thework suggests a pathway for tuning the magnetic properties of MAX phases. (c) 2018 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license.
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| 9. |
- Liu, Yanfeng, et al.
(författare)
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Mo1.33C MXene-Assisted PEDOT:PSS Hole Transport Layer for High-Performance Bulk-Heterojunction Polymer Solar Cells
- 2020
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Ingår i: ACS APPLIED ELECTRONIC MATERIALS. - : AMER CHEMICAL SOC. - 2637-6113. ; 2:1, s. 163-169
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Tidskriftsartikel (refereegranskat)abstract
- Here, we report the usage of two-dimensional MXene, Mo1.33C-assisted poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as an efficient hole transport layer (HTL) to construct high-efficiency polymer solar cells. The composite HTLs are prepared by mixing Mo1.33C and PEDOT:PSS aqueous solution. The conventional devices based on Mo1.33C:PEDOT:PSS exhibit an average power conversion efficiency (PCE) of 9.2%, which shows a 13% enhancement compared to the reference devices. According to the results from hole mobilities, charge extraction probabilities, steady-state photoluminescence, and atomic force microscopy, the enhanced PCE can be ascribed to the improved charge transport and extraction properties of the HTL, along with the morphological improvement of the active layer on top. This work clearly demonstrates the feasibility to combine advantages of Mo1.33C MXene and PEDOT:PSS as the promising HTL in organic photovoltaics.
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| 10. |
- Lu, Jun, et al.
(författare)
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Theoretical and Experimental Exploration of a Novel In-Plane Chemically Ordered (Cr2/3M1/3)(2)AIC i-MAX Phase with M = Sc and Y
- 2017
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Ingår i: Crystal Growth & Design. - : AMER CHEMICAL SOC. - 1528-7483 .- 1528-7505. ; 17:11, s. 5704-5711
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Tidskriftsartikel (refereegranskat)abstract
- We have uncovered two inherently laminated transition metal carbides, (Cr2/3Sc1/3)(2)A1C and (Cr2/3Y1/3)(2)A1C, which display in-plane chemical order in the carbide sheet and a Kagome pattern in the Al layer. The phases belong to the most recently discovered family of so-called i-MAX phases. The materials were synthesized and the crystal structures were evaluated by means of analytical high resolution scanning transmission electron microscopy, selected area electron diffraction, and X-ray diffraction Rietveld refinement. An orthorhombic structure of space group Cmcm (#63) and a monoclinic structure of space group C2/c (#15) are solved. The compounds were investigated by first-principles calculations based on density functional theory, suggesting close to degenerate anti-ferro- and ferromagnetic spin states, dynamical and mechanical stability, and a Voigt bulk modulus in the range 134-152 GPa.
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