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Crystals, Volume 8, Issue 3 (March 2018)

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Cover Story (view full-size image) Cubic SrF2 (Fm3m) is known as a rather poor ionic conductor. Replacing parts of the Sr ions by [...] Read more.
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Open AccessArticle Synthesis and Characterization of Charge Transfer Salts Based on [M(dcdmp)2] (M = Au, Cu and Ni) with TTF Type Donors
Crystals 2018, 8(3), 141; https://doi.org/10.3390/cryst8030141
Received: 6 March 2018 / Revised: 16 March 2018 / Accepted: 17 March 2018 / Published: 20 March 2018
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Abstract
The charge transfer salts α-DT-TTF[Au(dcdmp)2] (1), BET-TTF[Au(dcdmp)2] (2M and 2T), α-DT-TTF[Cu(dcdmp)2] (3), ET[Cu(dcdmp)2] (4), (BET-TTF)2[Cu(dcdmp)2] (5), (ET)2[Ni(dcdmp)2]
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The charge transfer salts α-DT-TTF[Au(dcdmp)2] (1), BET-TTF[Au(dcdmp)2] (2M and 2T), α-DT-TTF[Cu(dcdmp)2] (3), ET[Cu(dcdmp)2] (4), (BET-TTF)2[Cu(dcdmp)2] (5), (ET)2[Ni(dcdmp)2] (6), and α-mtdt[Cu(dcdmp)2] (7) were obtained by electrocrystallization of different electron donor molecules derived from TTF (α-DT-TTF = alpha-dithiophene-tetrathiafulvalene; BET-TTF = (bis(ethylenethio)tetrathiafulvalene; ET = bis(ethylenedithio)-tetrathiafulvalene; α-mtdt = alpha-methylthiophenetetrathiafulvalene) in the presence of transition metal complex [M(dcdmp)2] (M = Au (III), Cu (III) and Ni (II)) (dcdmp = 2,3-dicyano-5,6-dimercaptopyrazine). Compounds 1 and 2 (2M and 2T) have a similar packing pattern composed of mixed stacks of alternating donor-acceptor molecules. For (BET-TTF)[Au(dcdmp)2] two different crystal structures (2M and 2T) were obtained indicating polymorphism. Compounds 3 and 4 are isostructural being composed of zigzag chains of alternating donor and acceptor molecules. The salts with a 2:1 stoichiometry, (BET-TTF)2[Cu(dcdmp)2] (5), and (ET)2[Ni(dcdmp)2] (6) present the donor molecules fully oxidized and [M(dcdmp)2] (M = Ni and Cu) in a dianionic state. The salt of the dissymmetric donor α-mtdt with [Cu(dcdmp)2], α-mtdt[Cu(dcdmp)2] (7) has a crystal structure composed of segregated donor stacks that are positioned in a head-to-head fashion and alternate with the anion stacks. All charge transfer salts (17) are modest semiconductors with conductivities in the range 10−1–10−5 S/cm, with the highest values obtained in α-DT-TTF salts, compounds 1 and 3. Full article
(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)
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Open AccessArticle The Jahn-Teller Distortion at High Pressure: The Case of Copper Difluoride
Crystals 2018, 8(3), 140; https://doi.org/10.3390/cryst8030140
Received: 14 February 2018 / Revised: 15 March 2018 / Accepted: 16 March 2018 / Published: 19 March 2018
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Abstract
The opposing effects of high pressure (in the GPa range) and the Jahn-Teller distortion led to many intriguing phenomena which are still not well understood. Here we report a combined experimental-theoretical study on the high-pressure behavior of an archetypical Jahn-Teller system, copper difluoride
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The opposing effects of high pressure (in the GPa range) and the Jahn-Teller distortion led to many intriguing phenomena which are still not well understood. Here we report a combined experimental-theoretical study on the high-pressure behavior of an archetypical Jahn-Teller system, copper difluoride (CuF2). At ambient conditions this compound adopts a distorted rutile structure of P21/c symmetry. Raman scattering measurements performed up to 29 GPa indicate that CuF2 undergoes a phase transition at 9 GPa. We assign the novel high-pressure phase to a distorted fluorite structure of Pbca symmetry, iso-structural with the ambient-pressure structure of AgF2. Density functional theory calculations indicate that the Pbca structure should transform to a non-centrosymmetric Pca21 polymorph above 30 GPa, which, in turn, should be replaced by a cotunnite phase (Pnma symmetry) at 72 GPa. The elongated octahedral coordination of the Cu2+ cation persists up to the Pca21Pnma transition upon which it is replaced by a capped trigonal prism geometry, still bearing signs of a Jahn-Teller distortion. The high-pressure phase transitions of CuF2 resembles those found for difluorides of transition metals of similar radius (MgF2, ZnF2, CoF2), although with a much wider stability range of the fluorite-type structures, and lower dimensionality of the high-pressure polymorphs. Our calculations indicate no region of stability of a nanotubular polymorph observed for the related AgF2 system. Full article
(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)
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Open AccessArticle Structurally Characterized Solvent-Induced Homotrinuclear Cobalt(II) N2O2-Donor Bisoxime-Type Complexes
Crystals 2018, 8(3), 139; https://doi.org/10.3390/cryst8030139
Received: 22 February 2018 / Revised: 13 March 2018 / Accepted: 15 March 2018 / Published: 19 March 2018
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Abstract
Four new solvent-induced Co(II) complexes with chemical formulae [{CoL(μ2-OAc)(MeOH)}2Co] (1), [{CoL(μ2-OAc)(EtOH)}2Co] (2), [{CoL(μ2-OAc)(Py)}2Co] (3) and [{CoL(μ2-OAc)(DMF)}2Co] (
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Four new solvent-induced Co(II) complexes with chemical formulae [{CoL(μ2-OAc)(MeOH)}2Co] (1), [{CoL(μ2-OAc)(EtOH)}2Co] (2), [{CoL(μ2-OAc)(Py)}2Co] (3) and [{CoL(μ2-OAc)(DMF)}2Co] (4) (H2L = 4-nitro-4′-chloro-2,2′-[(1,3-propylene)dioxybis(nitrilomethylidyne)]diphenol) have been synthesized and characterized by elemental analyses, FT–IR, UV–Vis spectra and single-crystal X-ray diffraction. Each of the prepared complexes, crystallizing in the space groups P–1 (1 and 4), P21/n (2) and P21/c (3), consists of three Co(II) atoms, two completely deprotonated (L)2− units, two μ2-acetato ligands and two coordinated solvent molecules. Although the four complexes 14 were synthesized in different solvents, it is worthwhile that the Co(II) atoms in the four complexes 14 adopt hexa–coordinated with slightly distorted octahedral coordination geometries, and the ratio of the ligand H2L to Co(II) atoms is 2:3. The complexes 24 possess a self-assembled infinite 1D, 2D and 1D supramolecular structures via the intermolecular hydrogen bonds, respectively. Magnetic measurement was performed in the complex 3. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Temperature Dependence of Crystal Structures and Band Parameters in Quantum Spin Liquid β′-EtMe3Sb[Pd(dmit)2]2 and Related Materials
Crystals 2018, 8(3), 138; https://doi.org/10.3390/cryst8030138
Received: 27 February 2018 / Revised: 14 March 2018 / Accepted: 15 March 2018 / Published: 17 March 2018
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Abstract
In an isostructural series of anion radical salts β′-(Me4-xEtxZ)[Pd(dmit)2]2 (Z = P, As, Sb; x = 0, 1, 2), [Pd(dmit)2]2 units form a two-dimensional Mott insulator layer with a quasi-isosceles triangular lattice.
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In an isostructural series of anion radical salts β′-(Me4-xEtxZ)[Pd(dmit)2]2 (Z = P, As, Sb; x = 0, 1, 2), [Pd(dmit)2]2 units form a two-dimensional Mott insulator layer with a quasi-isosceles triangular lattice. The anisotropy of the triangular lattice is characterized by a ratio of interdimer transfer integrals, t′/t. The crystal structures of EtMe3Sb, Me4Sb, Me4As, and Et2Me2As salts were determined in the range of 5–295 K by the single crystal X-ray diffraction technique. Interdimer transfer integrals, Fermi surface, and band structures at low temperatures were calculated by the tight binding method and the first-principles density-functional theory (DFT) method based on experimentally obtained crystal structures. Interdimer transfer integrals increased with lowering temperature. At 5 K, the ratio t′/t decreased by about 15% from the room temperature value in every salt. The relationship between the transfer integrals and interdimer S⋯S distances indicated that the change of the t′/t value with temperature was due to a thermal contraction, rather than the arch-shaped molecular distortion of the Pd(dmit)2 molecule associated with the cation dependence of t′/t. Full article
(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)
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Open AccessArticle Optical Conductivity in a Two-Dimensional Extended Hubbard Model for an Organic Dirac Electron System α-(BEDT-TTF)2I3
Crystals 2018, 8(3), 137; https://doi.org/10.3390/cryst8030137
Received: 25 February 2018 / Revised: 13 March 2018 / Accepted: 14 March 2018 / Published: 16 March 2018
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Abstract
The optical conductivity in the charge order phase is calculated in the two-dimensional extended Hubbard model describing an organic Dirac electron system α-(BEDT-TTF)2I3 using the mean field theory and the Nakano-Kubo formula. Because the interband excitation is characteristic in
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The optical conductivity in the charge order phase is calculated in the two-dimensional extended Hubbard model describing an organic Dirac electron system α -(BEDT-TTF) 2 I 3 using the mean field theory and the Nakano-Kubo formula. Because the interband excitation is characteristic in a two-dimensional Dirac electron system, a peak structure is found above the charge order gap. It is shown that the peak structure originates from the Van Hove singularities of the conduction and valence bands, where those singularities are located at a saddle point between two Dirac cones in momentum space. The frequency of the peak structure exhibits drastic change in the vicinity of the charge order transition. Full article
(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)
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Open AccessArticle Crystal Structure, Hydration, and Two-Fold/Single-Fold Diffusion Kinetics in Proton-Conducting Ba0.9La0.1Zr0.25Sn0.25In0.5O3−a Oxide
Crystals 2018, 8(3), 136; https://doi.org/10.3390/cryst8030136
Received: 15 February 2018 / Revised: 12 March 2018 / Accepted: 13 March 2018 / Published: 16 March 2018
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Abstract
In this work, hydration kinetics related to the incorporation of water into proton-conducting Ba0.9La0.1Zr0.25Sn0.25In0.5O3−a perovskite-type oxide are presented, with a recorded transition on temperature from a single-fold to a two-fold behavior. This
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In this work, hydration kinetics related to the incorporation of water into proton-conducting Ba0.9La0.1Zr0.25Sn0.25In0.5O3−a perovskite-type oxide are presented, with a recorded transition on temperature from a single-fold to a two-fold behavior. This can be correlated with an appearance of the electronic hole component of the conductivity at high temperatures. The collected electrical conductivity relaxation data allowed to calculate chemical diffusion coefficient D and surface exchange reaction coefficient k, as well as respective activation energies of their changes on temperature. Presented results are supplemented with a systematic characterization of the structural properties of materials synthesized at different temperatures, amount of incorporated water after hydration in different conditions, influence of water content on the crystal structure, as well as electrical conductivity in dry, H2O- and D2O-containing air, which enabled to evaluate proton (deuterium) conductivity. Full article
(This article belongs to the Special Issue Ceramic Conductors)
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Open AccessArticle The Formation Mechanism of Cu(In0.7Ga0.3)Se2 Nanoparticles and the Densification Trajectory of the Se-Rich Quaternary Target by Hot Pressing
Crystals 2018, 8(3), 135; https://doi.org/10.3390/cryst8030135
Received: 1 March 2018 / Revised: 14 March 2018 / Accepted: 14 March 2018 / Published: 15 March 2018
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Abstract
In this paper, a method to obtain the CuInGaSe2 (CIGS) absorber layer with an appropriate selenium content is put forward, in which a Se-rich target is used to deposit a CIGS thin-film and this film is annealed in a Se-free inert atmosphere.
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In this paper, a method to obtain the CuInGaSe2 (CIGS) absorber layer with an appropriate selenium content is put forward, in which a Se-rich target is used to deposit a CIGS thin-film and this film is annealed in a Se-free inert atmosphere. The key issue of this method is the preparation of a Se-rich target with a homogeneous composition and a high-density. The formation mechanism of CuInSe2 and CuGaSe2 is investigated and the results point to the intermediate phase Cu2−xSe playing a role of a nucleation core. The sintering densification trajectory of the target with the addition of extra selenium is researched. Additionally, an effective way to avoid the sintering defects is proposed. Finally, a conversion efficiency of 11.2% for the CIGS solar cell is reached by sputtering from the obtained Se-rich target. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Application of La-Doped SrTiO3 in Advanced Metal-Supported Solid Oxide Fuel Cells
Crystals 2018, 8(3), 134; https://doi.org/10.3390/cryst8030134
Received: 31 January 2018 / Revised: 9 March 2018 / Accepted: 10 March 2018 / Published: 13 March 2018
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Abstract
Composite materials frequently allow the drawbacks of single components to be overcome thanks to a synergistic combination of material- and structure-specific features, leading to enhanced and also new properties. This is the case of a metallic-ceramic composite, a nickel-chromium-aluminum (NiCrAl) foam impregnated with
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Composite materials frequently allow the drawbacks of single components to be overcome thanks to a synergistic combination of material- and structure-specific features, leading to enhanced and also new properties. This is the case of a metallic-ceramic composite, a nickel-chromium-aluminum (NiCrAl) foam impregnated with La-doped Strontium Titanate (LST). This particular cermet has very interesting properties that can be used in different fields of application, namely: mechanical robustness provided by the metal foam; and chemical stability in harsh conditions of temperature and atmosphere by promotion of a thin protective layer of alumina (Al2O3); high electronic conductivity given by a percolating ceramic conducting phase, i.e., La-doped Strontium Titanate. In this paper, its application as a current collector in a metal-supported Solid Oxide Fuel Cells (SOFC) was studied. Firstly, the electronic properties of different compositions, stoichiometric and under stoichiometric, of LST were analyzed to choose the best one in terms of conductivity and phase purity. Then, LST chemical stability was studied in the presence of Al2O3 at different temperatures, gas compositions and aging times. Finally, stability and conductivity of LST-impregnated NiCrAl foam composite materials were measured, and LST was found to be fully compatible with the NiCrAl foam, as no reactions were detected in oxidizing and reducing atmosphere after up to 300 h operation at 750 °C and 900 °C between the Al2O3 layer and LST. Results showed that the composite is suitable as a current collector in innovative designs of metal-supported SOFC, like the Evolve cell, in which the metallic part is supposed not only to provide the structural stability to the cell, but also to play the role of current collector due to the impregnation of ceramic material. Full article
(This article belongs to the Special Issue Ceramic Conductors)
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Open AccessReview Dislocation Structures in Low-Angle Grain Boundaries of α-Al2O3
Crystals 2018, 8(3), 133; https://doi.org/10.3390/cryst8030133
Received: 14 February 2018 / Revised: 6 March 2018 / Accepted: 7 March 2018 / Published: 12 March 2018
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Abstract
Alumina (α-Al2O3) is one of the representative high-temperature structural materials. Dislocations in alumina play an important role in its plastic deformation, and they have attracted much attention for many years. However, little is known about their core atomic structures,
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Alumina (α-Al2O3) is one of the representative high-temperature structural materials. Dislocations in alumina play an important role in its plastic deformation, and they have attracted much attention for many years. However, little is known about their core atomic structures, with a few exceptions, because of lack of experimental observations at the atomic level. Low-angle grain boundaries are known to consist of an array of dislocations, and they are useful to compose dislocation structures. So far, we have systematically fabricated several types of alumina bicrystals with a low-angle grain boundary and characterized the dislocation structures by transmission electron microscopy (TEM). Here, we review the dislocation structures in { 11 2 ¯ 0 } / [ 0001 ] , { 11 2 ¯ 0 } / 1 1 ¯ 00 , { 1 1 ¯ 00 } / 11 2 ¯ 0 , ( 0001 ) / 1 1 ¯ 00 , { 1 ¯ 104 } / 11 2 ¯ 0 , and ( 0001 ) / [ 0001 ] low-angle grain boundaries of alumina. Our observations revealed the core atomic structures of b = 1 / 3 11 2 ¯ 0 edge and screw dislocations, 1 1 ¯ 00 edge dislocation, and 1 / 3 1 ¯ 101 edge and mixed dislocations. Moreover, the stacking faults on { 11 2 ¯ 0 } , { 1 1 ¯ 00 } , and ( 0001 ) planes formed due to the dissociation reaction of the dislocations are discussed, focusing on their atomic structure and formation energy. Full article
(This article belongs to the Special Issue Crystal Dislocations: Their Impact on Physical Properties of Crystals)
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Open AccessArticle Experimental Electron Density Distribution in Two Cocrystals of Betaines with p-Hydroxybenzoic Acid
Crystals 2018, 8(3), 132; https://doi.org/10.3390/cryst8030132
Received: 8 February 2018 / Revised: 5 March 2018 / Accepted: 8 March 2018 / Published: 10 March 2018
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Abstract
Experimental determination of electron density distribution in crystals by means of high-resolution X-ray diffraction allows, among others, for studying the details of intra- and inter-molecular interactions. In case of co-crystals, this method may help in finding the conditions of creating such species. The
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Experimental determination of electron density distribution in crystals by means of high-resolution X-ray diffraction allows, among others, for studying the details of intra- and inter-molecular interactions. In case of co-crystals, this method may help in finding the conditions of creating such species. The results of such analysis for two co-crystals containing betaines, namely trigonelline (TRG: nicotinic acid N-methylbetaine, IUPAC name: 1-methylpyridinium-3-carboxylate) and N-methylpiperidine betaine (MPB: 1-methylpiperidinium-1-yl-carboxylate) with p-hydroxybenzoic acid (HBA) are reported. TRG-HBA crystallizes as a hydrate. For both of the co-crystals, high-quality diffraction data were collected up to sinθ/λ = 1.13 Å−1. Hansen-Coppens multipolar model was then applied for modelling the electron density distribution and Atoms-In-Molecules approach was used for detailed analysis of interactions in crystals. A number of intermolecular interactions was identified, ranging from strong O-H···O hydrogen bonds through C-H···O to C-H···π and π···π interactions. Correlations between the geometrical characteristics of the contacts and the features of their critical points were analyzed in detail. Atomic charges show that in zwitterionic species there are regions of opposite charges, rather than charges that are localized on certain atoms. In case of MPB-HBA, a significant charge transfer between the components of co-crystal (0.5 e) was found, as opposed to TRG-HBA, where all of the components are almost neutral. Full article
(This article belongs to the Special Issue Experimental and Theoretical Electron Density Analysis of Crystals)
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Open AccessArticle Direct Rehydrogenation of LiBH4 from H-Deficient Li2B12H12−x
Crystals 2018, 8(3), 131; https://doi.org/10.3390/cryst8030131
Received: 22 January 2018 / Revised: 23 February 2018 / Accepted: 6 March 2018 / Published: 9 March 2018
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Abstract
Li2B12H12 is commonly considered as a boron sink hindering the reversible hydrogen sorption of LiBH4. Recently, in the dehydrogenation process of LiBH4 an amorphous H-deficient Li2B12H12−x phase was observed. In
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Li2B12H12 is commonly considered as a boron sink hindering the reversible hydrogen sorption of LiBH4. Recently, in the dehydrogenation process of LiBH4 an amorphous H-deficient Li2B12H12−x phase was observed. In the present study, we investigate the rehydrogenation properties of Li2B12H12−x to form LiBH4. With addition of nanostructured cobalt boride in a 1:1 mass ratio, the rehydrogenation properties of Li2B12H12−x are improved, where LiBH4 forms under milder conditions (e.g., 400 °C, 100 bar H2) with a yield of 68%. The active catalytic species in the reversible sorption reaction is suggested to be nonmetallic CoxB (x = 1) based on 11B MAS NMR experiments and its role has been discussed. Full article
(This article belongs to the Special Issue Properties and Applications of Novel Light Metal Hydrides)
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Open AccessArticle Mechanochemical Synthesis and Crystal Structure of the Lidocaine-Phloroglucinol Hydrate 1:1:1 Complex
Crystals 2018, 8(3), 130; https://doi.org/10.3390/cryst8030130
Received: 8 February 2018 / Revised: 28 February 2018 / Accepted: 6 March 2018 / Published: 9 March 2018
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Abstract
Molecular complexation is a strategy used to modify the physicochemical or biopharmaceutical properties of an active pharmaceutical ingredient. Solvent assisted grinding is a common method used to obtain solid complexes in the form of cocrystals. Lidocaine is a drug used as an anesthetic
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Molecular complexation is a strategy used to modify the physicochemical or biopharmaceutical properties of an active pharmaceutical ingredient. Solvent assisted grinding is a common method used to obtain solid complexes in the form of cocrystals. Lidocaine is a drug used as an anesthetic and for the treatment of chronic pain, which bears in its chemical structure an amide functional group able to form hydrogen bonds. Polyphenols are used as cocrystal coformers due to their ability to form O–H···X (X = O, N) hydrogen bond interactions. The objective of this study was to exploit the ability of phloroglucinol to form molecular complexes with lidocaine by liquid assisted grinding. The formation of the complex was confirmed by the shift of the O–H and C=O stretching bands in the IR spectra of the polycrystalline ground powders, suggesting the formation of O–H···O=C hydrogen bonds. Hydration of the complexes also was confirmed by IR spectroscopy and by powder X-ray diffraction. The molecular structure was determined by single crystal X-ray diffraction. Full article
(This article belongs to the Special Issue Polymorphism of Mechanochemically Synthesized Cocrystals)
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Open AccessArticle The Influence of Vertical Vibration on Nanoscale Friction: A Molecular Dynamics Simulation Study
Crystals 2018, 8(3), 129; https://doi.org/10.3390/cryst8030129
Received: 15 January 2018 / Revised: 24 February 2018 / Accepted: 7 March 2018 / Published: 9 March 2018
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Abstract
The influence of vibration on friction at the nanoscale was studied via molecular dynamics (MD) simulations. The results show that average friction increases in a high-frequency range. This can be attributed to the vibration of the tip following vibration excitation, which results in
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The influence of vibration on friction at the nanoscale was studied via molecular dynamics (MD) simulations. The results show that average friction increases in a high-frequency range. This can be attributed to the vibration of the tip following vibration excitation, which results in peaks of repulsive interaction between tip and substrate and leads to higher friction. However, when the frequency is lower than a certain value, friction decreases. This is because vibration excitation results not in an obvious vibration of the tip but in a slightly larger interface distance, which leads to a decrease in friction. Full article
(This article belongs to the Special Issue Graphene Mechanics)
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Open AccessReview Thickness-Dependent Strain Rate Sensitivity of Nanolayers via the Nanoindentation Technique
Crystals 2018, 8(3), 128; https://doi.org/10.3390/cryst8030128
Received: 14 January 2018 / Revised: 19 February 2018 / Accepted: 21 February 2018 / Published: 9 March 2018
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Abstract
The strain rate sensitivity (SRS) and dislocation activation volume are two inter-related material properties for understanding thermally-activated plastic deformation, such as creep. For face-centered-cubic metals, SRS normally increases with decreasing grain size, whereas the opposite holds for body-center-cubic metals. However, these findings are
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The strain rate sensitivity (SRS) and dislocation activation volume are two inter-related material properties for understanding thermally-activated plastic deformation, such as creep. For face-centered-cubic metals, SRS normally increases with decreasing grain size, whereas the opposite holds for body-center-cubic metals. However, these findings are applicable to metals with average grain sizes greater than tens of nanometers. Recent studies on mechanical behaviors presented distinct deformation mechanisms in multilayers with individual layer thickness of 20 nanometers or less. It is necessary to estimate the SRS and plastic deformation mechanisms in this regime. Here, we review a new nanoindentation test method that renders reliable hardness measurement insensitive to thermal drift, and its application on SRS of Cu/amorphous-CuNb nanolayers. The new technique is applied to Cu films and returns expected SRS values when compared to conventional tensile test results. The SRS of Cu/amorphous-CuNb nanolayers demonstrates two distinct deformation mechanisms depending on layer thickness: dislocation pileup-dominated and interface-mediated deformation mechanisms. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness) Printed Edition available
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Open AccessArticle Structure of the Basal Edge Dislocation in ZnO
Crystals 2018, 8(3), 127; https://doi.org/10.3390/cryst8030127
Received: 19 January 2018 / Revised: 5 March 2018 / Accepted: 6 March 2018 / Published: 8 March 2018
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Abstract
Basal dislocations having a Burgers vector of 1/3<21¯1¯0> in zinc oxide (ZnO) with the wurtzite structure are known to strongly affect physical properties in bulk. However, the core structure of the basal dislocation remains unclear. In the present
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Basal dislocations having a Burgers vector of 1/3<2 1 ¯ 1 ¯ 0> in zinc oxide (ZnO) with the wurtzite structure are known to strongly affect physical properties in bulk. However, the core structure of the basal dislocation remains unclear. In the present study, ZnO bicrystals with a {2 1 ¯ 1 ¯ 0}/<01 1 ¯ 0> 2° low-angle tilt grain boundary were fabricated by diffusion bonding. The resultant dislocation core structure was observed by using scanning transmission electron microscopy (STEM) at an atomic resolution. It was found that a basal edge dislocation in α-type is dissociated into two partial dislocations on the (0001) plane with a separation distance of 1.5 nm, indicating the glide dissociation. The Burgers vectors of the two partial dislocations were 1/3<1 1 ¯ 00> and 1/3<10 1 ¯ 0>, and the stacking fault between the two partials on the (0001) plane has a formation energy of 0.14 J/m2. Although the bicrystals have a boundary plane of {2 1 ¯ 1 ¯ 0}, the boundary basal dislocations do not exhibit dissociation along the boundary plane, but along the (0001) plane perpendicular to the boundary plane. From DFT calculations, the stacking fault on the (0001) plane was found to be much more stable than that on {2 1 ¯ 1 ¯ 0}. Such an extremely low energy of the (0001) stacking fault can realize transverse dissociation of the basal dislocation of ZnO. Full article
(This article belongs to the Special Issue Crystal Dislocations: Their Impact on Physical Properties of Crystals)
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