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Crystals, Volume 9, Issue 5 (May 2019) – 51 articles

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Cover Story (view full-size image) The Al- and Fe-oxide-hydroxides systems share many isostructures. While Al10O14(OH)2(akdalaite) and [...] Read more.
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Open AccessArticle
Multifrequency Driven Nematics
Crystals 2019, 9(5), 275; https://doi.org/10.3390/cryst9050275 - 27 May 2019
Cited by 2 | Viewed by 860
Abstract
Liquid crystals act on the amplitude and the phase of a wave front under applied electric fields. Ordinary LCs are known as field induced birefringence, thus both phase and amplitude modulation strongly depend on the voltage controllable molecular tilt. In this work we [...] Read more.
Liquid crystals act on the amplitude and the phase of a wave front under applied electric fields. Ordinary LCs are known as field induced birefringence, thus both phase and amplitude modulation strongly depend on the voltage controllable molecular tilt. In this work we present electrooptical properties of novel liquid crystal (LC) mixture with frequency tunable capabilities from 100Hz to 10 KHz at constant applied voltage. The frequency tunability of presented mixtures shown here came from composition of three different families of rodlike liquid crystals. Dielectric measurements are reported for the compounds constituting frequency-controlled birefringence liquid crystal. Characterization protocols allowing the optimum classification of different components of this mixture, paying attention to all relevant parameters such as anisotropic polarizability, dielectric anisotropy, and dipole moment are presented. Full article
(This article belongs to the Special Issue Liquid Crystal Optical Device) Printed Edition available
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Open AccessEditorial
Special Issue Editorial: Ionic Liquid Crystals
Crystals 2019, 9(5), 274; https://doi.org/10.3390/cryst9050274 - 27 May 2019
Cited by 4 | Viewed by 711
Abstract
The term “Ionic Liquid Crystals” (ILCs) clearly results from the blending of the well-known “Ionic Liquids” (ILs) and “Liquid Crystals” (LCs) names of the corresponding materials [...] Full article
(This article belongs to the Special Issue Ionic Liquid Crystals) Printed Edition available
Open AccessArticle
Floating Zone Growth of Sr Substituted Han Purple: Ba0.9Sr0.1CuSi2O6
Crystals 2019, 9(5), 273; https://doi.org/10.3390/cryst9050273 - 27 May 2019
Viewed by 1029
Abstract
We present a route to grow single crystals of Ba 0.9 Sr 0.1 CuSi 2 O 6 suitable for inelastic neutron studies via the floating zone technique. Neutron single crystal diffraction was utilized to check their bulk quality and orientation. Finally, the high [...] Read more.
We present a route to grow single crystals of Ba 0.9 Sr 0.1 CuSi 2 O 6 suitable for inelastic neutron studies via the floating zone technique. Neutron single crystal diffraction was utilized to check their bulk quality and orientation. Finally, the high quality of the grown crystals was proven by X-ray diffraction and magnetic susceptibility. Full article
(This article belongs to the Special Issue Optical Floating Zone and Crystals Grown by this Method)
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Open AccessReview
Recent Advances in Adaptive Liquid Crystal Lenses
Crystals 2019, 9(5), 272; https://doi.org/10.3390/cryst9050272 - 25 May 2019
Cited by 24 | Viewed by 1698
Abstract
An adaptive-focus lens is a device that is capable of tuning its focal length by means of an external stimulus. Numerous techniques for the demonstration of such devices have been reported thus far. Moving beyond traditional solutions, several new approaches have been proposed [...] Read more.
An adaptive-focus lens is a device that is capable of tuning its focal length by means of an external stimulus. Numerous techniques for the demonstration of such devices have been reported thus far. Moving beyond traditional solutions, several new approaches have been proposed in recent years based on the use of liquid crystals, which can have a great impact in emerging applications. This work focuses on the recent advances in liquid crystal lenses with diameters larger than 1 mm. Recent demonstrations and their performance characteristics are reviewed, discussing the advantages and disadvantages of the reported technologies and identifying the challenges and future prospects in the active research field of adaptive-focus liquid crystal (LC) lenses. Full article
(This article belongs to the Special Issue Liquid Crystal Optical Device) Printed Edition available
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Open AccessArticle
Simultaneous SAXS-WAXS Experiments on Semi-Crystalline Polymers: Example of PA11 and Its Brill Transition
Crystals 2019, 9(5), 271; https://doi.org/10.3390/cryst9050271 - 24 May 2019
Cited by 2 | Viewed by 1571
Abstract
This manuscript of the special issue “Microstructural Evolution and Mechanical Behavior of Semi-Crystalline Polymers” aims to show that Small Angle X-ray Scattering (SAXS) and Wide Angle X-ray Scattering (WAXS) experiments performed simultaneously constitute a unique tool to obtain valuable information on the hierarchical [...] Read more.
This manuscript of the special issue “Microstructural Evolution and Mechanical Behavior of Semi-Crystalline Polymers” aims to show that Small Angle X-ray Scattering (SAXS) and Wide Angle X-ray Scattering (WAXS) experiments performed simultaneously constitute a unique tool to obtain valuable information on the hierarchical structure of semi-crystalline polymers. These structural quantitative data are needed to model macroscopic properties of polymeric materials, for example their mechanical properties. To illustrate our point, we focus our study on the structure and morphology of polyamide 11. Through a simultaneous SAXS-WAXS experiment, we show that the absence of enthalpic signal in Differential Scanning Calorimetry (DSC) is not synonymous with the absence of structural and morphological evolution with temperature. The case of a thermally activated crystal–crystal transition, the Brill transition, is particularly detailed. Through this SAXS-WAXS study, we show, among other points, and for the first time, that the periodicity of crystalline lamellae (LP) changes at the transition, probably due to a modification of the amorphous phase’s free volume at the Brill transition. We also explain the crucial role of annealing to stabilize polymeric materials that may experience temperature changes over their lifetime. The influence of the annealing on the perfection of crystalline structure, morphology and mechanical behavior is more particularly studied. Full article
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Open AccessPerspective
New Directions in Metal Phosphonate and Phosphinate Chemistry
Crystals 2019, 9(5), 270; https://doi.org/10.3390/cryst9050270 - 24 May 2019
Cited by 29 | Viewed by 4391
Abstract
In September 2018, the First European Workshop on Metal Phosphonates Chemistry brought together some prominent researchers in the field of metal phosphonates and phosphinates with the aim of discussing past and current research efforts and identifying future directions. The scope of this perspective [...] Read more.
In September 2018, the First European Workshop on Metal Phosphonates Chemistry brought together some prominent researchers in the field of metal phosphonates and phosphinates with the aim of discussing past and current research efforts and identifying future directions. The scope of this perspective article is to provide a critical overview of the topics discussed during the workshop, which are divided into two main areas: synthesis and characterisation, and applications. In terms of synthetic methods, there has been a push towards cleaner and more efficient approaches. This has led to the introduction of high-throughput synthesis and mechanochemical synthesis. The recent success of metal–organic frameworks has also promoted renewed interest in the synthesis of porous metal phosphonates and phosphinates. Regarding characterisation, the main advances are the development of electron diffraction as a tool for crystal structure determination and the deployment of in situ characterisation techniques, which have allowed for a better understanding of reaction pathways. In terms of applications, metal phosphonates have been found to be suitable materials for several purposes: they have been employed as heterogeneous catalysts for the synthesis of fine chemicals, as solid sorbents for gas separation, notably CO2 capture, as materials for electrochemical devices, such as fuel cells and rechargeable batteries, and as matrices for drug delivery. Full article
(This article belongs to the Special Issue Metal Phosphonates and Phosphinates) Printed Edition available
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Open AccessReview
Reading and Misreading 8-oxoguanine, a Paradigmatic Ambiguous Nucleobase
Crystals 2019, 9(5), 269; https://doi.org/10.3390/cryst9050269 - 23 May 2019
Cited by 3 | Viewed by 1236
Abstract
7,8-Dihydro-8-oxoguanine (oxoG) is the most abundant oxidative DNA lesion with dual coding properties. It forms both Watson–Crick (anti)oxoG:(anti)C and Hoogsteen (syn)oxoG:(anti)A base pairs without a significant distortion of a B-DNA helix. DNA polymerases bypass oxoG [...] Read more.
7,8-Dihydro-8-oxoguanine (oxoG) is the most abundant oxidative DNA lesion with dual coding properties. It forms both Watson–Crick (anti)oxoG:(anti)C and Hoogsteen (syn)oxoG:(anti)A base pairs without a significant distortion of a B-DNA helix. DNA polymerases bypass oxoG but the accuracy of nucleotide incorporation opposite the lesion varies depending on the polymerase-specific interactions with the templating oxoG and incoming nucleotides. High-fidelity replicative DNA polymerases read oxoG as a cognate base for A while treating oxoG:C as a mismatch. The mutagenic effects of oxoG in the cell are alleviated by specific systems for DNA repair and nucleotide pool sanitization, preventing mutagenesis from both direct DNA oxidation and oxodGMP incorporation. DNA translesion synthesis could provide an additional protective mechanism against oxoG mutagenesis in cells. Several human DNA polymerases of the X- and Y-families efficiently and accurately incorporate nucleotides opposite oxoG. In this review, we address the mutagenic potential of oxoG in cells and discuss the structural basis for oxoG bypass by different DNA polymerases and the mechanisms of the recognition of oxoG by DNA glycosylases and dNTP hydrolases. Full article
(This article belongs to the Special Issue Noncanonical Nucleobases)
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Open AccessArticle
Effect of Sectional Polymerization Process on Tunable Twist Structure Liquid Crystal Filters
Crystals 2019, 9(5), 268; https://doi.org/10.3390/cryst9050268 - 23 May 2019
Viewed by 763
Abstract
The effect of sectional polymerization process on tunable filters with cholesteric liquid crystal (CLC) and blue phase liquid crystal (BPLC) is demonstrated. The bandwidths of the polymer-stabilized cholesteric liquid crystal (PSCLC) and polymer-stabilized blue phase liquid crystal (PSBPLC) filters can be broadened by [...] Read more.
The effect of sectional polymerization process on tunable filters with cholesteric liquid crystal (CLC) and blue phase liquid crystal (BPLC) is demonstrated. The bandwidths of the polymer-stabilized cholesteric liquid crystal (PSCLC) and polymer-stabilized blue phase liquid crystal (PSBPLC) filters can be broadened by the holding treatment without distortion. The reflection bandwidth of the CLC filter can be broadened from 120 nm to 220 nm, and that of the BPLC filter can be broadened from 45 nm to 140 nm. Meanwhile, the intensity of reflection can be retained very well. The central wavelength of polymer-stabilized CLC filter can be thermally tuned from 1614 nm to 1460 nm with a stable wide bandwidth. The tunable C-band CLC filter and BPLC filter show great potential application in multi- and hyper-spectral systems and wide-band color filters. Full article
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Open AccessEditorial
Compounds with Polar Metallic Bonding
Crystals 2019, 9(5), 267; https://doi.org/10.3390/cryst9050267 - 22 May 2019
Viewed by 670
Abstract
Recently, I witnessed a discussion amongst solid state chemists whether the term polar intermetallic bonding was necessary or dispensable, whether a conceptual discernation of this special class of intermetallic compounds was indicated or spurious [...] Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding) Printed Edition available
Open AccessArticle
Transformation of the Topological Phase and the Edge Modes of Double-Bilayer Bismuthene with Inter-Bilayer Spacing
Crystals 2019, 9(5), 266; https://doi.org/10.3390/cryst9050266 - 22 May 2019
Cited by 1 | Viewed by 854
Abstract
The transformations of the topological phase and the edge modes of a double-bilayer bismuthene were investigated with first-principles calculations and Green’s function as the inter-bilayer spacing increased from 0 Å to 10 Å. At a critical spacing of 2 Å, a topological phase [...] Read more.
The transformations of the topological phase and the edge modes of a double-bilayer bismuthene were investigated with first-principles calculations and Green’s function as the inter-bilayer spacing increased from 0 Å to 10 Å. At a critical spacing of 2 Å, a topological phase transition from a topological insulator to a band insulator resulting from a band inversion between the highest valence band and the second lowest conduction band, was observed, and this was understood based on the particular orbital characters of the band inversion involved states. The edge modes of double-bilayer bismuthene survived the phase transition. When d was 2 Å < d < 4 Å, the interaction between the edge modes of two separated bismuthene bilayers induced an anti-crossing gap and resulted in a trivial band connection. At and beyond 4 Å, the two bilayers behavior decoupled entirely. The results demonstrate the transformability of the topological phase and the edge modes with the inter-bilayer spacing in double-bilayer bismuthene, which may be useful for spintronic applications. Full article
(This article belongs to the Special Issue Recent Advances in Novel Topological Materials)
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Open AccessArticle
Ordering of Rods near Surfaces: Concentration Effects
Crystals 2019, 9(5), 265; https://doi.org/10.3390/cryst9050265 - 21 May 2019
Viewed by 788
Abstract
We study the orientation of rods in the neighborhood of a surface. A semi-infinite region in two different situations is considered: (i) the rods are located close to a flat wall and (ii) the rods occupy the space that surrounds a sphere. In [...] Read more.
We study the orientation of rods in the neighborhood of a surface. A semi-infinite region in two different situations is considered: (i) the rods are located close to a flat wall and (ii) the rods occupy the space that surrounds a sphere. In a recent paper we investigated a similar problem: the interior of a sphere, with a fixed concentration of rods. Here, we allow for varying concentration, the rods are driven from a reservoir to the neighborhood of the surface by means of a tunable chemical potential. In the planar case, the particle dimensions are irrelevant. In the curved case, we consider cylinders with dimensions comparable to the radius of curvature of the sphere; as they come close to the surface, they have to accommodate to fill the available space, leading to a rich orientational profile. These systems are studied by a mapping onto a three-state Potts model with annealed disorder on a semi-infinite lattice; two order parameters describe the system: the occupancy and the orientation. The Hamiltonian is solved using a mean-field approach producing recurrence relations that are iterated numerically and we obtain various interesting results: the system undergoes a first order transition just as in the bulk case; the profiles do not have a smooth decay but may present a step and we search for the factors that determine their shape. The prediction of such steps may be relevant in the field of self-assembly of colloids and nanotechnology. Full article
(This article belongs to the Special Issue New Trends in Lyotropic Liquid Crystals)
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Open AccessArticle
Semiperiodic Ultra-Broadband Double-Grating to Improve c-Si Thin-Film Solar Cell’s Optical Absorption, through Numerical Structural Optimization
Crystals 2019, 9(5), 264; https://doi.org/10.3390/cryst9050264 - 21 May 2019
Cited by 1 | Viewed by 961
Abstract
Plasmonic gratings provide effective photon management techniques in thin-film solar cells, capable of extending the optical thickness of the solar cell’s active layer. However, the ultra-broadband nature of such application makes an optimal design of the grating structure quite challenging, since a fully [...] Read more.
Plasmonic gratings provide effective photon management techniques in thin-film solar cells, capable of extending the optical thickness of the solar cell’s active layer. However, the ultra-broadband nature of such application makes an optimal design of the grating structure quite challenging, since a fully periodic grating operates only in specific spectral ranges. To achieve a more broadband design, semiperiodicity is introduced, which, due to having controllable disorder, is an apt solution in broadband optical applications. In this work, semiperiodic double gratings as a broadband photon management technique are introduced in order to improve the optical absorption of c-Si thin-film solar cells, and optimized through numerical structural optimization. Physical parameters of both front and back gratings are determined taking the spectrally integrated optical absorption as the figure of merit and subsequently a semiperiodic double grating is established through adding defects to the fully periodic structure. It is shown that such semiperiodic structure is capable of enhancing the spectrally integrated optical absorption 88.6 % compared to a reference structure without gratings. Full article
(This article belongs to the Special Issue Advances in Thin Film Solar Cells)
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Open AccessReview
Magnetron Sputtering for ZnO:Ga Scintillation Film Production and Its Application Research Status in Nuclear Detection
Crystals 2019, 9(5), 263; https://doi.org/10.3390/cryst9050263 - 20 May 2019
Cited by 3 | Viewed by 1093
Abstract
As a wide band-gap and direct transition semiconductor material, ZnO has good scintillation performance and strong radiation resistance, but it also has a serious self-absorption phenomenon that affects its light output. After being doped with Ga, it can be used for the scintillator [...] Read more.
As a wide band-gap and direct transition semiconductor material, ZnO has good scintillation performance and strong radiation resistance, but it also has a serious self-absorption phenomenon that affects its light output. After being doped with Ga, it can be used for the scintillator of ultra-fast scintillating detectors to detect X-ray, gamma, neutron, and charged particles with extremely fast response and high light output. Firstly, the basic properties, defects, and scintillation mechanism of ZnO crystals are introduced. Thereafter, magnetron sputtering, one of the most attractive production methods for producing ZnO:Ga film, is introduced including the principle of magnetron sputtering and its technical parameters’ influence on the performance of ZnO:Ga. Finally, ZnO:Ga film’s application research status is presented as a scintillation material in the field of radiation detection, and it is concluded that some problems need to be urgently solved for its wider application. Full article
(This article belongs to the Special Issue Crystals, Films and Nanocomposite Scintillators)
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Open AccessReview
Peculiarities in the Director Reorientation and the NMR Spectra Evolution in a Nematic Liquid Crystals under the Effect of Crossed Electric and Magnetic Fields
Crystals 2019, 9(5), 262; https://doi.org/10.3390/cryst9050262 - 20 May 2019
Cited by 1 | Viewed by 694
Abstract
The illustrative description of the field-induced peculiarities of the director reorientation in the microsized nematic volumes under the effect of crossed magnetic B and electric E fields have been proposed. The most interesting feature of such configuration is that the nematic phase becomes [...] Read more.
The illustrative description of the field-induced peculiarities of the director reorientation in the microsized nematic volumes under the effect of crossed magnetic B and electric E fields have been proposed. The most interesting feature of such configuration is that the nematic phase becomes unstable after applying the strong E . The theoretical analysis of the reorientational dynamics of the director field provides an evidence for the appearance of the spatially periodic patterns in response to applied large E directed at an angle α to B . The feature of this approach is that the periodic distortions arise spontaneously from a homogeneously aligned nematic sample that ultimately induces a faster response than in the uniform mode. The nonuniform rotational modes involve additional internal elastic distortions of the conservative nematic system and, as a result, these deformations decrease of the viscous contribution U vis to the total energy U of the nematic phase. In turn, that decreasing of U vis leads to decrease of the effective rotational viscosity coefficient γ eff ( α ) . That is, a lower value of γ eff ( α ) , which is less than one in the bulk nematic phase, gives the less relaxation time τ on ( α ) γ eff ( α ) , when α is bigger than the threshold value α th . The results obtained by Deuterium NMR spectroscopy confirm theoretically obtained dependencies of τ on ( α ) on α . Full article
(This article belongs to the Special Issue Nuclear Magnetic Resonance of Liquid Crystals)
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Open AccessArticle
A Magnetic-Dependent Vibration Energy Harvester Based on the Tunable Point Defect in 2D Magneto-Elastic Phononic Crystals
Crystals 2019, 9(5), 261; https://doi.org/10.3390/cryst9050261 - 19 May 2019
Cited by 3 | Viewed by 987
Abstract
In this work, an innovative vibration energy harvester is designed by using the point defect effect of two-dimensional (2D) magneto-elastic phononic crystals (PCs) and the piezoelectric effect of piezoelectric material. A point defect is formed by removing the central Tenfenol-D rod to confine [...] Read more.
In this work, an innovative vibration energy harvester is designed by using the point defect effect of two-dimensional (2D) magneto-elastic phononic crystals (PCs) and the piezoelectric effect of piezoelectric material. A point defect is formed by removing the central Tenfenol-D rod to confine and enhance vibration energy into a spot, after which the vibration energy is electromechanically converted into electrical energy by attaching a piezoelectric patch into the area of the point defect. Numerical analysis of the point defect can be carried out by the finite element method in combination with the supercell technique. A 3D Zheng-Liu (Z-L) model which accurately describes the magneto-mechanical coupling constitutive behavior of magnetostrictive material is adopted to obtain variable band structures by applied magnetic field and pre-stress along the z direction. The piezoelectric material is utilized to predict the output voltage and power based on the capacity to convert vibration energy into electrical energy. For the proposed tunable vibration energy harvesting system, numerical results illuminate that band gaps (BGs) and defect bands of the in-plane mixed wave modes (XY modes) can be adjusted to a great extent by applied magnetic field and pre-stress, and thus a much larger range of vibration frequency and more broad-distributed energy can be obtained. The defect bands in the anti-plane wave mode (Z mode), however, have a slight change with applied magnetic field, which leads to a certain frequency range of energy harvesting. These results can provide guidance for the intelligent control of vibration insulation and the active design of continuous power supply for low power devices in engineering. Full article
(This article belongs to the Special Issue Sonic and Photonic Crystals) Printed Edition available
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Open AccessArticle
Theoretical Model and Experimental Investigations on Solution-Mediated Polymorphic Transformation of Theophylline: From Polymorph I to Polymorph II
Crystals 2019, 9(5), 260; https://doi.org/10.3390/cryst9050260 - 19 May 2019
Cited by 3 | Viewed by 1023
Abstract
In this work, theophylline was selected as the model compound to study and simulate the solution-mediated polymorphic transformation. The polymorph I and polymorph II of theophylline were prepared and fully characterized. Raman and UV spectra methods were carried out to observe the phase [...] Read more.
In this work, theophylline was selected as the model compound to study and simulate the solution-mediated polymorphic transformation. The polymorph I and polymorph II of theophylline were prepared and fully characterized. Raman and UV spectra methods were carried out to observe the phase transformation of theophylline from polymorph I to polymorph II at different temperatures. The theoretical models, including dissolution model, nucleation model, and growth model, were established to describe and simulate the transformation processes. By combination of experiments and simulations, the controlling steps of the transformation processes were discussed. The effects of temperature and/or solvent on the transformation processes were evaluated. This work can shed light on the polymorphic transformation processes. Full article
(This article belongs to the Special Issue Anti-Solvent Crystallization)
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Open AccessArticle
Bacterial Effect on the Crystallization of Mineral Phases in a Solution Simulating Human Urine
Crystals 2019, 9(5), 259; https://doi.org/10.3390/cryst9050259 - 18 May 2019
Cited by 3 | Viewed by 1047
Abstract
The effect of bacteria that present in the human urine (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Staphylococcus aureus) was studied under the conditions of biomimetic synthesis. It was shown that the addition of bacteria significantly affects both the phase composition [...] Read more.
The effect of bacteria that present in the human urine (Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Staphylococcus aureus) was studied under the conditions of biomimetic synthesis. It was shown that the addition of bacteria significantly affects both the phase composition of the synthesized material and the position of crystallization boundaries of the resulting phosphate phases, which can shift toward more acidic (struvite, apatite) or toward more alkaline (brushite) conditions. Under conditions of oxalate mineralization, bacteria accelerate the nucleation of calcium oxalates by almost two times and also increase the amount of oxalate precipitates along with phosphates and stabilize the calcium oxalate dihydrate (weddellite). The multidirectional changes in the pH values of the solutions, which are the result of the interaction of all system components and the crystallization process, were analyzed. The obtained results are the scientific basis for understanding the mechanisms of bacterial involvement in stone formation within the human body and the creation of biotechnological methods that inhibit this process. Full article
(This article belongs to the Special Issue Mineralogical Crystallography) Printed Edition available
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Open AccessCommunication
Morphologically Controlled Synthesis of Cs2SnCl6 Perovskite Crystals and Their Photoluminescence Activity
Crystals 2019, 9(5), 258; https://doi.org/10.3390/cryst9050258 - 18 May 2019
Viewed by 1202
Abstract
The Cs2SnX6 perovskites have attracted much attention due to excellent optoelectronic properties and high stability. In the present work, we have focused on the morphology control and photoluminescence characteristics of the Cs2SnCl6 perovskite crystals. The synthesis process [...] Read more.
The Cs2SnX6 perovskites have attracted much attention due to excellent optoelectronic properties and high stability. In the present work, we have focused on the morphology control and photoluminescence characteristics of the Cs2SnCl6 perovskite crystals. The synthesis process of the Cs2SnCl6 crystals includes two stages composed of the formation of initial crystals and the growth of Cs2SnCl6; the later originated from the oxidization of CsSnCl3. This process has been confirmed by Scanning electron microscope (SEM) and X-rays diffraction (XRD). By controlling the concentration of the initial reactants and hydrochloric acid in the solution to change the supersaturation of the solution, different crystal morphologies, such as truncated octahedron, octahedron, hexapod, quasi-sphere, have been obtained. In relatively a low supersaturation solution, the amount of growth units dominates the crystal growth process to obtain the hexapod and self-assembly crystals. In contrast, in relatively high supersaturation solution, nucleation predominates to yield small size truncated octahedrons and near-spherical Cs2SnCl6 crystals. The synthesized Cs2SnCl6 crystals have shown a wide emission band peaking at 450 nm with full width at half maximum (FWHM) 63 nm due to the defects introduced by Sn2+. The photoluminescence intensities of crystals synthesized at various conditions exhibited considerable difference, which was about 60 times between the highest and the lowest. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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Open AccessReview
Historical Perspective on Diffraction Line-Profile Analyses for Crystals Containing Defect Clusters
Crystals 2019, 9(5), 257; https://doi.org/10.3390/cryst9050257 - 17 May 2019
Cited by 1 | Viewed by 935
Abstract
Deviations of crystal diffraction line profiles from those predicted by the dynamical theory of diffraction for perfect crystals provide a window into the microscopic distributions of defects within non-perfect crystals. This overview provides a perspective on key theoretical, computational, and experimental developments associated [...] Read more.
Deviations of crystal diffraction line profiles from those predicted by the dynamical theory of diffraction for perfect crystals provide a window into the microscopic distributions of defects within non-perfect crystals. This overview provides a perspective on key theoretical, computational, and experimental developments associated with the analysis of diffraction line profiles for crystals containing statistical distributions of point defect clusters, e.g., dislocation loops, precipitates, and stacking fault tetrahedra. Pivotal theoretical developments beginning in the 1940s are recalled and discussed in terms of their impact on the direction of theoretical and experimental investigations of lattice defects in the 1960s, the 1970s, and beyond, as both experimental and computational capabilities advanced. The evolution of experimental measurements and analysis techniques, as stimulated by theoretical and computational progress in understanding the distortion fields surrounding defect clusters, is discussed. In particular, consideration is given to determining dislocation loop densities and separate size distributions for vacancy and interstitial type loops, and to the internal strain and size distributions for coherent precipitates. Full article
(This article belongs to the Special Issue X-ray and neutron Line Profile Analysis of Microstructures)
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Open AccessArticle
Crystal Structure Optimization and Gibbs Free Energy Comparison of Five Sulfathiazole Polymorphs by the Embedded Fragment QM Method at the DFT Level
Crystals 2019, 9(5), 256; https://doi.org/10.3390/cryst9050256 - 17 May 2019
Cited by 1 | Viewed by 1118
Abstract
Molecular crystal plays an important role in many fields of science and technology, but it often crystallizes in different polymorphs with different physical properties. To guide the experimental synthesis of candidate materials, the atomic-scale model is frequently used to predict the most stable [...] Read more.
Molecular crystal plays an important role in many fields of science and technology, but it often crystallizes in different polymorphs with different physical properties. To guide the experimental synthesis of candidate materials, the atomic-scale model is frequently used to predict the most stable polymorph and its structural properties. Here, we show how an ab initio method can be used to achieve a rapid and accurate prediction of sulfathiazole crystal polymorphs (an antibiotic drug), based on the Gibbs free energy calculation and Raman spectra analysis. At the atmospheric pressure and the temperature of 300 K, we demonstrate that form III (FIII) is the most stable structure of sulfathiazole. The agreement between the predicted and experimental crystal structures corresponds to the order of stability for five sulfathiazole polymorphs as FI < FV < FIV < FII < FIII, which is achieved by employing the density functional theory (DFT) calculations. Full article
(This article belongs to the Special Issue Polymorphism in Crystals)
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Open AccessEditor’s ChoiceArticle
The Fabrication of Calcium Alginate Beads as a Green Sorbent for Selective Recovery of Cu(Ⅱ) from Metal Mixtures
Crystals 2019, 9(5), 255; https://doi.org/10.3390/cryst9050255 - 17 May 2019
Cited by 8 | Viewed by 1311
Abstract
Calcium alginate (CA) beads as a green sorbent were easily fabricated in this study using sodium alginate crosslinking with CaCl2, and the crosslinking pathway was the exchange between the sodium ion of α-L-guluronic acid and Ca(II). The experimental study was conducted [...] Read more.
Calcium alginate (CA) beads as a green sorbent were easily fabricated in this study using sodium alginate crosslinking with CaCl2, and the crosslinking pathway was the exchange between the sodium ion of α-L-guluronic acid and Ca(II). The experimental study was conducted on Cu(II), Cd(II), Ni(II) and Zn(II) as the model heavy metals and the concentration was determined by inductively coupled plasma optical emission spectrometry (ICP-OES). The characterization and sorption behavior of the CA beads were analyzed in detail via using scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The adsorption experiments demonstrated that the CA beads exhibited a high removal efficiency for the selective adsorption of Cu(II) from the tetra metallic mixture solution and an excellent adsorption capacity of the heavy metals separately. According to the isotherm studies, the maximum uptake of Cu(II) could reach 107.53 mg/g, which was significantly higher than the other three heavy metal ions in the tetra metallic mixture solution. Additionally, after five cycles of adsorption and desorption, the uptake rate of Cu(II) on CA beads was maintained at 92%. According to the properties mentioned above, this material was assumed to be applied to reduce heavy metal pollution or recover valuable metals from waste water. Full article
(This article belongs to the Special Issue Layered Double Hydroxides)
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Open AccessArticle
Atomistic Modeling of Various Doped Mg2NiH4 as Conversion Electrode Materials for Lithium Storage
Crystals 2019, 9(5), 254; https://doi.org/10.3390/cryst9050254 - 17 May 2019
Cited by 2 | Viewed by 870
Abstract
In this work, we have compared the potential applications of nine different elements doped Mg2NiH4 as conversion-type electrode materials in Li-ion batteries by means of state-of-the-art Density functional theory calculations. The electrochemical properties, such as specific capacity, volume change and [...] Read more.
In this work, we have compared the potential applications of nine different elements doped Mg2NiH4 as conversion-type electrode materials in Li-ion batteries by means of state-of-the-art Density functional theory calculations. The electrochemical properties, such as specific capacity, volume change and average voltage, as well as the atomic and electronic structures of different doped systems have been investigated. The Na doping can improve the electrochemical capacity of the pristine material. Si and Ti doping can reduce the band gap and benefit the electronic conductivity of electrode materials. All of the nine doping elements can help to reduce the average voltage of negative electrodes and lead to reasonable volume changes. According to the computational screening, the Na, Si and Ti doping elements are thought to be promising to enhance the comprehensive properties of pure material. This theoretical study is proposed to encourage and expedite the development of metal-hydrides based lithium-storage materials. Full article
(This article belongs to the Special Issue Ab Initio Study of the Energy Storage Crystalline Materials)
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Open AccessArticle
Protein Crystallization in Ionic-Liquid Hydrogel Composite Membranes
Crystals 2019, 9(5), 253; https://doi.org/10.3390/cryst9050253 - 17 May 2019
Cited by 1 | Viewed by 1081
Abstract
Protein crystallization is a powerful purification tool. It is the first step for crystallographic structural investigations, and can be preparatory for biotechnological applications. However, crystallizing proteins is challenging and methods to control the crystallization process are needed. Ionic-liquid hydrogel composite membranes (IL-HCMs) have [...] Read more.
Protein crystallization is a powerful purification tool. It is the first step for crystallographic structural investigations, and can be preparatory for biotechnological applications. However, crystallizing proteins is challenging and methods to control the crystallization process are needed. Ionic-liquid hydrogel composite membranes (IL-HCMs) have been used here as material capable of supporting protein crystallization and hosting grown crystals. We found that IL-HCMs affect the selection mechanism of glucose isomerase (GI) polymorphs and make GI crystals grow completely immersed into the hydrogel layer. X-ray diffraction studies show that IL ions do not bind to the protein, likely because IL molecules are constrained in the polymeric framework. Our GI crystal structures have been compared with many existing GI crystal structures using multivariate analysis tools, allowing a comprehensive overview of factors determining structural similarities, i.e., temperature variations and external stresses exerted during or after crystal growth, such as dehydration or presence of hydrogel of a different nature. GI crystals grown on IL-HCM fit perfectly in this framework, showing typical features induced by external forces. Overall, protein crystallization by IL-HCMs show potential for biotechnological applications, as it could constitute a natural means for containing crystallized enzymes in working conditions. Full article
(This article belongs to the Special Issue Protein Crystallography)
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Open AccessArticle
The Effect of Internal Free Surfaces on Void Swelling of Irradiated Pure Iron Containing Subsurface Trenches
Crystals 2019, 9(5), 252; https://doi.org/10.3390/cryst9050252 - 15 May 2019
Viewed by 990
Abstract
We studied the effects of internal free surfaces on the evolution of ion-induced void swelling in pure iron. The study was initially driven by the motivation to introduce a planar free-surface defect sink at depths that would remove the injected interstitial effect from [...] Read more.
We studied the effects of internal free surfaces on the evolution of ion-induced void swelling in pure iron. The study was initially driven by the motivation to introduce a planar free-surface defect sink at depths that would remove the injected interstitial effect from ion irradiation, possibly enhancing swelling. Using the focused ion beam technique, deep trenches were created on a cross section of pure iron at various depths, so as to create bridges of thickness ranging from 0.88 μm to 1.70 μm. Samples were then irradiated with 3.5 MeV Fe2+ ions at 475 °C to a fluence corresponding to a peak displacement per atom dose of 150 dpa. The projected range of 3.5 MeV Fe2+ ions is about 1.2 μm so the chosen bridge thicknesses involved fractions of the ion range, thicknesses comparable to the mean ion range (peak of injected interstitial distribution), and thicknesses beyond the full range. It was found that introduction of such surfaces did not enhance swelling but actually decreased it, primarily because there were now two denuded zones with a combined stronger influence than that of the injected interstitial. The study suggests that such strong surface effects must be considered for ion irradiation studies of thin films or bridge-like structures. Full article
(This article belongs to the Special Issue Nanostructured Ferritic Alloys)
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Open AccessArticle
Magnetic Properties of Quasi-One-Dimensional Crystals Formed by Graphene Nanoclusters and Embedded Atoms of the Transition Metals
Crystals 2019, 9(5), 251; https://doi.org/10.3390/cryst9050251 - 15 May 2019
Cited by 2 | Viewed by 793
Abstract
Using the density-matrix renormalization group method and quantum Monte Carlo simulation, we studied numerically the energy spectrum and thermodynamics of the quantum Heisenberg spin model for narrow graphene nanoribbons and their derivatives with periodically embedded heteroatoms. For several nanoribbon structures we found macroscopic [...] Read more.
Using the density-matrix renormalization group method and quantum Monte Carlo simulation, we studied numerically the energy spectrum and thermodynamics of the quantum Heisenberg spin model for narrow graphene nanoribbons and their derivatives with periodically embedded heteroatoms. For several nanoribbon structures we found macroscopic ground state spin, gapless lowest excitation spectra and intermediate magnetization plateaus at low temperatures. We also studied the lowest energy states of frustrated systems formed by triangular graphitic clusters connected by bridged ions of transition metals. On the base of many-body perturbation theory and the exact diagonalization method, we showed the possibility of spin switching for this model due to the change the corresponding coupling parameters. Full article
(This article belongs to the Special Issue Quantum and Molecular Mechanic Analysis of Crystalline Materials)
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Open AccessArticle
Quasi-Liquid Layer on Ice and Its Effect on the Confined Freezing of Porous Materials
Crystals 2019, 9(5), 250; https://doi.org/10.3390/cryst9050250 - 14 May 2019
Cited by 3 | Viewed by 955
Abstract
Freezing of the water confined in thin pores can be destructive to the porous frame, but the effect of the quasi-liquid layer (QLL) between the confined ice and the pore walls remains still far from being fully understood. In the present study, the [...] Read more.
Freezing of the water confined in thin pores can be destructive to the porous frame, but the effect of the quasi-liquid layer (QLL) between the confined ice and the pore walls remains still far from being fully understood. In the present study, the physical origins of the intermediate phase of QLL were discussed by thermodynamic analyses. Different interactions on QLL bring different models to estimate its thickness, which generally decays with temperature decreasing. Four representative models of QLL thickness were selected to unveil its effect on the growing rates and extents of ice in a concrete. The engineering consequences of the confined freezing were then discussed in the aspects of effective pore pressures built from the confined ice growth and deformations framed by a poro-elastic model. Overall, thickening QLL depresses ice growing rates and contents and, consequentially, decreases pore pressures and material deformations during freezing. The QLL corrections also narrow the gaps between the predicted and measured freezing deformations. The findings of this study contribute to profound understandings of confined freezing that may bridge over physical principles and engineering observations. Full article
(This article belongs to the Special Issue Ice Crystals) Printed Edition available
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Open AccessArticle
Nematic and Cholesteric Liquid Crystal Structures in Cells with Tangential-Conical Boundary Conditions
Crystals 2019, 9(5), 249; https://doi.org/10.3390/cryst9050249 - 14 May 2019
Cited by 2 | Viewed by 1125
Abstract
Orientational structures formed in nematic and cholesteric layers with tangential-conical boundary conditions have been investigated. LC cells with one substrate specifying the conical surface anchoring and another substrate specifying the tangential one have been considered. The director configurations and topological defects have been [...] Read more.
Orientational structures formed in nematic and cholesteric layers with tangential-conical boundary conditions have been investigated. LC cells with one substrate specifying the conical surface anchoring and another substrate specifying the tangential one have been considered. The director configurations and topological defects have been identified analyzing the texture patterns obtained by polarizing microscope in comparison with the structures and optical textures calculated by free energy minimization procedure of director field and finite-difference time-domain method, respectively. The domains, periodic structures and two-dimensional defects proper to the LC cells with tangential-conical anchoring have been studied depending on the layer thickness and cholesteric pitch. Full article
(This article belongs to the Special Issue Advances in Cholesteric Liquid Crystals) Printed Edition available
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Open AccessArticle
Negative Thermal Expansivity of Ice: Comparison of the Monatomic mW Model with the All-Atom TIP4P/2005 Water Model
Crystals 2019, 9(5), 248; https://doi.org/10.3390/cryst9050248 - 14 May 2019
Cited by 1 | Viewed by 805
Abstract
We calculate the thermal expansivity of ice I for the monatomic mW model using the quasi-harmonic approximation. It is found that the original mW model is unable to reproduce the negative thermal expansivity experimentally observed at low temperatures. A simple prescription is proposed [...] Read more.
We calculate the thermal expansivity of ice I for the monatomic mW model using the quasi-harmonic approximation. It is found that the original mW model is unable to reproduce the negative thermal expansivity experimentally observed at low temperatures. A simple prescription is proposed to recover the negative thermal expansion by re-adjusting the so-called tetrahedrality parameter, λ. We investigate the relation between the λ value and the Grüneisen parameter to explain the origin of negative thermal expansion in the mW model and compare it with an all-atom water model that allows the examination of the effect of the rotational motions on the volume of ice. Full article
(This article belongs to the Special Issue Ice Crystals) Printed Edition available
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Open AccessArticle
Insight into the Optoelectronic and Thermoelectric Properties of Mn Doped ZnTe from First Principles Calculation
Crystals 2019, 9(5), 247; https://doi.org/10.3390/cryst9050247 - 13 May 2019
Cited by 4 | Viewed by 1049
Abstract
Using DFT band structure simulations together with semi-classical Boltzmann transport kinetics equations, we have explored the optoelectronic and transport features of MnxZn1−xTe (x = 8% and 16%) crystals. Optimization of the doping and related technological processes it is extremely [...] Read more.
Using DFT band structure simulations together with semi-classical Boltzmann transport kinetics equations, we have explored the optoelectronic and transport features of MnxZn1−xTe (x = 8% and 16%) crystals. Optimization of the doping and related technological processes it is extremely important for optimization of the technological parameters. The Generalized Gradient Approximation is applied to compute the corresponding band structure parameters. We have applied the Generalized Gradient Approximation Plus U (GGA+U). We have demonstrated that MnxZn1−xTe (x = 8% and 16%) is a direct type band semiconductor with principal energy gap values equal to 2.20 and 2.0 eV for x = 8% and 16%, respectively. The energy gap demonstrates significant decrease with increasing Mn content. Additionally, the origin of the corresponding bands is explored from the electronic density of states. The optical dispersion functions are calculated from the spectra of dielectric function. The theoretical simulations performed unambiguously showed that the titled materials are simultaneously promising optoelectronic and thermoelectric devices. The theoretical simulations performed showed ways for amendment of their transport properties by replacement of particular ions. Full article
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Open AccessArticle
Structural Chemistry of Akdalaite, Al10O14(OH)2, the Isostructural Aluminum Analogue of Ferrihydrite
Crystals 2019, 9(5), 246; https://doi.org/10.3390/cryst9050246 - 12 May 2019
Cited by 2 | Viewed by 1508
Abstract
As part of an effort to characterize clusters and intermediate phases likely to be encountered along solution reaction pathways that produce iron and aluminum oxide-hydroxides from Fe and Al precursors, the complete structure of Al10O14(OH)2 (akdalaite) was determined [...] Read more.
As part of an effort to characterize clusters and intermediate phases likely to be encountered along solution reaction pathways that produce iron and aluminum oxide-hydroxides from Fe and Al precursors, the complete structure of Al10O14(OH)2 (akdalaite) was determined from a combination of single-crystal X-ray diffraction (SC-XRD) data collected at 100 K to define the Al and O positions, and solid-state nuclear magnetic resonance (NMR) and neutron powder diffraction (NPD) data collected at room temperature (~300 K) to precisely determine the nature of hydrogen in the structure. Two different synthesis routes produced different crystal morphologies. Using an aluminum oxyhydroxide floc made from mixing AlCl3 and 0.48 M NaOH, the product had uniform needle morphology, while using nanocrystalline boehmite (Vista Chemical Company Catapal D alumina) as the starting material produced hexagonal plates. Akdalaite crystallizes in the space group P63mc with lattice parameters of a = 5.6244(3) Å and c = 8.8417(3) Å (SC-XRD) and a = 5.57610(2) Å and c = 8.77247(6) Å (NPD). The crystal structure features Al13O40 Keggin clusters. The structural chemistry of akdalaite is nonideal but broadly conforms to that of ferrihydrite, the nanomineral with which it is isostructural. Full article
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