The recent discovery of chemical ordering in quaternary borides offers new ways of exploring properties and functionalities of these laminated phases. Here, we have synthesized and investigated ...chemical ordering of the laminated Mo4MnSiB2 (T2) phase, thereby introducing a magnetic element into the family of materials coined o-MAB phases. By X-ray diffraction and scanning transmission electron microscopy, we provide evidence for out-of-plane chemical ordering of Mo and Mn, with Mo occupying the 16l site and Mn preferentially residing in the 4c site. Mn and B constitute quasi-two-dimensional layers in the laminated material. We have therefore also studied the magnetic properties by magnetometry, and no sign of long-range magnetic order is observed. An initial assessment of the magnetic ordering has been further studied by density functional theory (DFT) calculations, and while we find an antiferromagnetic configuration to be the most stable one, ferromagnetic ordering is very close in energy.
Zero and low field nuclear magnetic resonance measurements have been performed on MAX phase samples (Cr1−x Mn x )2AC with A = Ge and Ga in order to obtain local microscopic information on the nature ...of magnetism in this system. Our results unambiguously provide evidence for the existence of long-range magnetic order in (Cr0.96Mn0.04)2GeC and for (Cr0.93Mn0.07)2GaC, but not for (Cr0.97Mn0.03)2GaC. We point to a possible dependence of long range magnetic order in these MAX phase compounds on the A atom.
Recently, we presented a family of in-plane chemically ordered transition metal borides of the general formula (M-2/3M-1/3")(2)AlB2. Here, we investigate incorporation of magnetic rare earth (RE) ...elements into this structure by synthesis and analysis of Mo4/3RE2/3AlB2, where RE = Ho, Tb, and Er. The crystal structure is verified by X-ray diffraction and scanning transmission electron microscopy, while the composition is derived from energy dispersive X-ray analysis. Through magnetization measurements, we also show that Mo4/3Ho2/3AlB2 orders antiferromagnetically below 9 K. We suggest that (M-2/3M-1/3")(2)AlB2 could potentially be a versatile platform for new magnetic materials, in 3D as well as 2D. GARPHICS IMPACT STATEMENT This paper introduces magnetic elements to i-MAB phases family with a formula of Mo4/3RE2/3AlB2 (RE = Ho, Er, and Tb), which opens a venue for further exploration of chemically ordered magnetic materials.
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.
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)2AlC and (W2/3Y1/3)2AlC. ...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 μm 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.
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.
Abstract
MXenes, a young family of 2D transition metal carbides/nitrides, show great potential in electrochemical energy storage applications. Herein, a high performance ultrathin flexible ...solid‐state supercapacitor is demonstrated based on a Mo
1.33
C MXene with vacancy ordering in an aligned layer structure MXene/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) composite film posttreated with concentrated H
2
SO
4
. The flexible solid‐state supercapacitor delivers a maximum capacitance of 568 F cm
−3
, an ultrahigh energy density of 33.2 mWh cm
−3
and a power density of 19 470 mW cm
−3
. The Mo
1.33
C MXene/PEDOT:PSS composite film shows a reduction in resistance upon H
2
SO
4
treatment, a higher capacitance (1310 F cm
−3
) and improved rate capabilities than both pristine Mo
1.33
C MXene and the nontreated Mo
1.33
C/PEDOT:PSS composite films. The enhanced capacitance and stability are attributed to the synergistic effect of increased interlayer spacing between Mo
1.33
C MXene layers due to insertion of conductive PEDOT, and surface redox processes of the PEDOT and the MXene.
We report muon spin rotation (\(\mu\)SR) and neutron diffraction on the rare-earth based magnets (Mo\(_{2/3}\)RE\(_{1/3}\))\(_2\)AlC, also predicted as parent materials for 2D derivatives, where RE = ...Nd, Gd (only (\(\mu\)SR), Tb, Dy, Ho and Er. By crossing information between the two techniques, we determine the magnetic moment (\(m\)), structure, and dynamic properties of all compounds. We find that only for RE = Nd and Gd the moments are frozen on a microsecond time scale. Out of these two, the most promising compound for a potential 2D high (\(m\)) magnet is the Gd variant, since the parent crystals are pristine with \(m = 6.5 \pm 0.5 \mu_B\), Néel temperature of \(29 \pm 1\) K, and the magnetic anisotropy between in and out of plane coupling is smaller than \(10^{-8}\). This result suggests that magnetic ordering in the Gd variant is dominated by in-plane magnetic interactions and should therefore remain stable if exfoliated into 2D sheets.
We report on synthesis and characterization of a new magnetic nanolaminate (V,Mn)(3)GaC2, which is the first magnetic MAX phase of a 312 stoichiometry. Atomically resolved energy dispersive X-ray ...mapping of epitaxial thin films reveals a tendency of alternate chemical ordering between V and Mn, with atomic layers composed of primarily one element only. Magnetometry measurements reveal a ferromagnetic response between 50 K and 300 K, with indication of a magnetic ordering temperature well above room temperature. (C) 2016 Author(s).
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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