Correction for '2,5-Furandicarboxylic acid as a linker for lanthanide coordination polymers: the role of heteroaromatic π-π stacking and hydrogen bonding' by Manesh Kumar
et al.
,
New J. Chem.
, ...2019, DOI:
10.1039/c8nj05701j
.
The plastic deformation in hcp metals is complex, with the associated dislocation core structures and properties not well understood on many slip planes in most hcp metals. A first step in ...establishing the dislocation properties is to examine the stable stacking fault energy and its structure on relevant slip planes. However, this has been perplexing in the hcp structure due to additional in-plane displacements on both sides of the slip plane. Here, density functional theory guided by crystal symmetry analysis is used to study all relevant stable stacking faults in 6 hcp metals (Mg, Ti, Zr, Re, Zn, Cd). Specially, the stable stacking fault energy, position, and structure on the Basal, Prism I and II, Pyramidal I and II planes are determined using all-periodic supercells with full atomic relaxation. All metals show similar stacking fault position and structure as dictated by crystal symmetry, but the associated stacking fault energy, being governed by the atomic bonding, differs significantly among them. Stacking faults on all the slip planes except the Basal plane show substantial out-of-plane displacements while stacking faults on the Prism II, Pyramidal I and II planes show additional in-plane displacements, all extending to multiple atom layers. The in-plane displacements are not captured in the standard computational approach for stacking faults, and significant differences are shown in the energies of such stacking faults between the standard approach and fully-relaxed case. The existence of well-defined stable stacking fault on the Pyramidal planes suggests zonal dislocations are unlikely. Calculations on the equilibrium partial separation further suggests 〈c + a〉 dissociation into three partials on the Pyramidal I plane is unlikely and 〈c〉 dissociation on Prism planes is unlikely to be stable against climb-dissociation onto the Basal planes in these metals.
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Ultrathin NiMn-LDH nanosheets in situ grown on nickel foam are prepared, in which suitable dose of Mn doping can change the electronic configuration, construct special stacking fault disorder to ...alleviate undesired structural change and produce a new impurity band to enhance electronic conductivity. These merits make NiMn-LDH //AC achieve superior cycling performance of at high current density of 10 A g−1.
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•NiMn-LDH/NF possesses high specific capacity, excellent rate capability and superior cycling performance.•Mn-dopant improves electrochemical performance of α-Ni(OH)2 by special stacking fault disorder and changed band gap energy.•EXAFS data, XRD patterns and DFT calculations prove the novel stacking fault disorder between NiO2 slabs.
Mn-doping engineering route has been demonstrated an effective way to enhance the electronic conductivity of α-Ni(OH)2 as a hybrid supercapacitor electrode material. However, the problem of limited cycling lifetime remains unsolved and the structural evolution of Mn-doping at the atomic level is still under debate. Herein, a novel life span improving strategy is proposed to modulate the electronic configuration and the layer stacking mode of Mn doped Ni(OH)2 (NiMn-LDH) in situ grown on nickel foam by controlling the Mn doping level (~6% atomic) and occupied site (3a site only). XRD, EXAFS and DFT calculations have been employed to confirm that the modified electronic configuration due to Mn doping induces local contraction of metal-O/metal bond length and increases curve degree within ab planes, which further introduces special stacking fault disorder between layers to stabilize the structure. Finally, the suitable-dose Mn doped NiMn-LDH exhibits high capacity (1498 C g−1 at 2 A g−1), excellent rate capability and superior cycling performance (almost 100% capacity retention after 30,000 cycles at 50 A g−1). This work demonstrates modulating local environment by suitable dose of metal doping can boost the cycling performance of nickel-based electrode materials for applications in energy storage and conversion.
Three compounds with phenyl and pentafluorophenyl rings bridged by (CH2)3 and (CH2)2SiMe2 units were synthesized by hydrosilylation and C−C coupling reactions. Their solid‐state structures are ...dominated by intermolecular π stacking interactions, primarily leading to dimeric or chain‐type aggregates. Analysis of free molecules in the gas phase by electron diffraction revealed the most abundant conformer to be significantly stabilized by intramolecular π–π interactions. For the silicon compounds, structures characterized by σ–π interactions between methyl and pentafluorophenyl groups are second lowest in energy and cannot be excluded completely by the gas electron diffraction experiments. C6H5(CH2)3C6F5, in contrast, is present as a single conformer. The gas‐phase structures served as a reference for the evaluation of a series of (dispersion‐corrected) quantum‐chemical calculations.
Undistorted structures of compounds with C6H5 and C6F5 groups linked by (CH2)3 and (CH2)2SiMe2 moieties show folding by intramolecular dispersion forces in the gas phase whereas in the solid state, extended conformers are adopted that interact intermolecularly. The experimental data served as a reference for the quality of quantum‐chemical calculations.
The powerful independent gradient model (IGM) method has been increasingly popular in visual analysis of intramolecular and intermolecular interactions in recent years. However, we frequently ...observed that there is an evident shortcoming of IGM map in graphically studying weak interactions, that is its isosurfaces are usually too bulgy; in these cases, not only the graphical effect is poor, but also the color on some areas on the isosurfaces is inappropriate and may lead to erroneous analysis conclusions. In addition, the IGM method was originally proposed based on promolecular density, which is quite crude and does not take actual electronic structure into account. In this article, we propose an improvement version of IGM, namely IGM based on Hirshfeld partition of molecular density (IGMH), which replaces the free‐state atomic densities involved in the IGM method with the atomic densities derived by Hirshfeld partition of actual molecular electron density. This change makes IGM have more rigorous physical background. A large number of application examples in this article, including molecular and periodic systems, weak and chemical bond interactions, fully demonstrate the important value of IGMH in intuitively understanding interactions in chemical systems. Comparisons also showed that the IGMH usually has markedly better graphical effect than IGM and overcomes known problems in IGM. Currently IGMH analysis has been supported in our wavefunction analysis code Multiwfn (http://sobereva.com/multiwfn). We hope that IGMH will become a new useful method among chemists for exploring interactions in wide variety of chemical systems.
We introduce a new method for visually studying interactions in chemical systems named independent gradient model based on Hirshfeld partition (IGMH). This method is able to clearly and graphically exhibit occurrence regions and types of interactions in broad range of systems, and it has evident advantages over the popular noncovalent interaction (NCI) and IGM methods. IGMH has been realized in our freely available wavefunction code Multiwfn.
Due to substantial phonon scattering induced by various structural defects, the in‐plane thermal conductivity (K) of graphene films (GFs) is still inferior to the commercial pyrolytic graphite sheet ...(PGS). Here, the problem is solved by engineering the structures of GFs in the aspects of grain size, film alignment, and thickness, and interlayer binding energy. The maximum K of GFs reaches to 3200 W m−1 K−1 and outperforms PGS by 60%. The superior K of GFs is strongly related to its large and intact grains, which are over four times larger than the best PGS. The large smooth features about 11 µm and good layer alignment of GFs also benefit on reducing phonon scattering induced by wrinkles/defects. In addition, the presence of substantial turbostratic‐stacking graphene is found up to 37% in thin GFs. The lacking of order in turbostratic‐stacking graphene leads to very weak interlayer binding energy, which can significantly decrease the phonon interfacial scattering. The GFs also demonstrate excellent flexibility and high tensile strength, which is about three times higher than PGS. Therefore, GFs with optimized structures and properties show great potentials in thermal management of form‐factor‐driven electronics and other high‐power‐driven systems.
Improved thermal and mechanical properties of graphene films can be achieved by structural engineering of the grain size, film alignment and thickness, surface flatness, and interlayer binding energy. The resulting graphene films offer an efficient heat dissipation solution for form‐factor‐driven electronics and other power‐driven systems that is superior to commonly used materials.
Stacking fault energy (SFE) plays an important role in deformation mechanisms and mechanical properties of face-centered cubic (fcc) metals and alloys. In many concentrated fcc alloys, the SFEs ...determined from density functional theory (DFT) calculations and experimental methods are found having opposite signs. Here, we show that the negative SFE by DFT reflects the thermodynamic instability of the fcc phase relative to the hexagonal close-packed one; while the experimentally determined SFEs are restricted to be positive by the models behind the indirect measurements. We argue that the common models underlying the experimental measurements of SFE fail in metastable alloys. In various concentrated solid solutions, we demonstrate that the SFEs obtained by DFT calculations correlate well with the primary deformation mechanisms observed experimentally, showing a better resolution than the experimentally measured SFEs. Furthermore, we believe that the negative SFE is important for understanding the abnormal behaviors of partial dislocations in metastable alloys under deformation. The present work advances the fundamental understanding of SFE and its relation to plastic deformations, and sheds light on future alloy design by physical metallurgy.
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•The common models underlying experimental measurements of stacking fault energy fail in metastable alloys.•Theoretical stacking fault energy correlates with the Gibbs free energy difference between the fcc and hcp phases.•Ab initio calculated stacking fault energy correlates nicely with the prevailing deformation mechanism.•Negative stacking fault energy plays critical role in understanding dislocation behaviors in metastable alloys.
Inspired by the popular deep learning architecture, deep stacking network (DSN), a specific deep model for polarimetric synthetic aperture radar (POLSAR) image classification is proposed in this ...paper, which is named Wishart DSN (W-DSN). First of all, a fast implementation of Wishart distance is achieved by a special linear transformation, which speeds up the classification of POLSAR image and makes it possible to use this polarimetric information in the following neural network (NN). Then, a single-hidden-layer NN based on the fast Wishart distance is defined for POLSAR image classification, which is named Wishart network (WN) and improves the classification accuracy. Finally, a multi-layer NN is formed by stacking WNs, which is in fact the proposed deep learning architecture W-DSN for POLSAR image classification and improves the classification accuracy further. In addition, the structure of WN can be expanded in a straightforward way by adding hidden units if necessary, as well as the structure of the W-DSN. As a preliminary exploration on formulating specific deep learning architecture for POLSAR image classification, the proposed methods may establish a simple but clever connection between POLSAR image interpretation and deep learning. The experiment results tested on real POLSAR image show that the fast implementation of Wishart distance is very efficient (a POLSAR image with 768 000 pixels can be classified in 0.53 s), and both the single-hidden-layer architecture WN and the deep learning architecture W-DSN for POLSAR image classification perform well and work efficiently.
A novel on‐line synergistic proconcentration strategy coupling field‐amplified sample stacking and micelle to cyclodextrin stacking for cationic analytes in capillary zone electrophoresis has been ...proposed and applied for the separation and determination of two alkaloids, matrine, and oxymatrine in complicated matrix samples. The approach was performed by the long injection of sample in a low‐conductivity sodium dodecyl benzene sulfonate solution followed by the injection of hydroxypropyl‐β‐cyclodextrin solution in higher conductivity. The stacking mechanism of this method has been expounded and parameters affecting stacking effect have been optimized in our study. Under the optimum experimental conditions, 169‐ and 218‐fold sensitivity improvements were achieved for matrine and oxymatrine when compared with normal injection. Analytical indicators including linearity, limits of detection, and reproducibility (intra‐ and inter‐day relative standard deviations) were evaluated. Moreover, sample matrix effect was studied using compound flavescent sophora and salicylic acid powder and spiked urine samples. The developed method is an attempt for the combination of micelle to cyclodextrin stacking with other stacking methods. It could be a good alternative choice for the determination of alkaloids in a complex sample matrix.
High-entropy alloys (HEAs) are an intriguing new class of metallic materials due to their unique mechanical behavior. Achieving a detailed understanding of structure–property relationships in these ...materials has been challenged by the compositional disorder that underlies their unique mechanical behavior. Accordingly, in this work, we employ first-principles calculations to investigate the nature of local chemical order and establish its relationship to the intrinsic and extrinsic stacking fault energy (SFE) in CrCoNi medium-entropy solid-solution alloys, whose combination of strength, ductility, and toughness properties approaches the best on record. We find that the average intrinsic and extrinsic SFE are both highly tunable, with values ranging from −43 to 30 mJ·m−2 and from −28 to 66 mJ·m−2, respectively, as the degree of local chemical order increases. The state of local ordering also strongly correlates with the energy difference between the face-centered cubic (fcc) and hexagonal close-packed (hcp) phases, which affects the occurrence of transformation-induced plasticity. This theoretical study demonstrates that chemical short-range order is thermodynamically favored in HEAs and can be tuned to affect the mechanical behavior of these alloys. It thus addresses the pressing need to establish robust processing–structure–property relationships to guide the science-based design of new HEAs with targeted mechanical behavior.
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