Crystals

8 pages, 3572 KiB

Open AccessArticle

Design of an Electrically Tunable Micro-Lens Based on Graded Photonic Crystal

by YongLe Qi, XiaoHong Sun, Shuai Wang, WenYang Li and ZhongYong Wang

Crystals 2018, 8(7), 303; https://doi.org/10.3390/cryst8070303 - 23 Jul 2018

Cited by 7 | Viewed by 3399

A micro-lens with an adjustable focal length (FL) is designed by using Graded Photonic Crystal (GPC) structures and a Polymer Dispersed Liquid Crystal (PDLC) material. The GPCs are formed by gradually changing the radius of the polymer rods in the Photonic Crystal (PC) [...] Read more.

A micro-lens with an adjustable focal length (FL) is designed by using Graded Photonic Crystal (GPC) structures and a Polymer Dispersed Liquid Crystal (PDLC) material. The GPCs are formed by gradually changing the radius of the polymer rods in the Photonic Crystal (PC) with square lattices of polymer rods in the background of Liquid Crystals (LCs). The electrically tunable focusing characteristics of the micro-lens are investigated by loading a continuous voltage source to change the LC rotation angle. The sensitivity of the focal shift in terms of LCs tilting angle is 0.152 λ(nm/deg). Moreover, the effect of the defects and deviations on the focusing characteristics are also analyzed. This research is crucial for future applications of the proposed device in the integrated photonics and adaptive optics. Full article

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18 pages, 10706 KiB

Open AccessArticle

Molecular Dynamics Analysis of Synergistic Effects of Ions and Winter Flounder Antifreeze Protein Adjacent to Ice-Solution Surfaces

by Tatsuya Yasui, Tadashi Kaijima, Ken Nishio and Yoshimichi Hagiwara

Crystals 2018, 8(7), 302; https://doi.org/10.3390/cryst8070302 - 22 Jul 2018

Cited by 2 | Viewed by 3285

Abstract

The control of freezing saline water at the micrometer level has become very important in cryosurgery and cryopreservation of stem cells and foods. Adding antifreeze protein to saline water is a promising method for controlling the freezing because the protein produces a gap [...] Read more.

The control of freezing saline water at the micrometer level has become very important in cryosurgery and cryopreservation of stem cells and foods. Adding antifreeze protein to saline water is a promising method for controlling the freezing because the protein produces a gap between the melting point and the freezing point. Furthermore, a synergistic effect of the solutes occurs in which the freezing point depression of a mixed solution is more noticeable than the sum of two freezing point depressions of single-solute solutions. However, the mechanism of this effect has not yet been clarified. Thus, we have carried out a molecular dynamics simulation on aqueous solutions of winter flounder antifreeze protein and sodium chloride or calcium chloride with an ice layer. The results show that the cations inhibit the hydrogen bond among water molecules not only in the salt solutions but also in the mixed solutions. This inhibition depends on the local number of ions and the valence of cations. The space for water molecules to form the hydrogen bonds becomes small in the case of the mixed solution of the protein and calcium chloride. These findings are consistent with the synergistic effect. In addition, it is found that the diffusion of ions near positively-charged residues is attenuated. This attenuation causes an increase in the possibility of water molecules staying near or inside the hydration shells of the ions. Furthermore, the first hydration shells of the cations become weak in the vicinity of the arginine, lysine and glutamic-acid residues. These factors can be considered to be possible mechanisms of the synergistic effect. Full article

(This article belongs to the Special Issue Advances in Computer Simulation Studies on Crystal Growth)

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9 pages, 2767 KiB

Open AccessArticle

Does Thermosalient Effect Have to Concur with a Polymorphic Phase Transition? The Case of Methscopolamine Bromide

by Teodoro Klaser, Jasminka Popović, José A. Fernandes, Serena C. Tarantino, Michele Zema and Željko Skoko

Crystals 2018, 8(7), 301; https://doi.org/10.3390/cryst8070301 - 21 Jul 2018

Cited by 14 | Viewed by 5304

Abstract

In this paper, we report for the first time an observed thermosalient effect that is not accompanied with a phase transition. Our experiments found that methscolopamine bromide—a compound chemically very similar to another thermosalient material, oxitropium bromide—exhibited crystal jumps during heating in the [...] Read more.

In this paper, we report for the first time an observed thermosalient effect that is not accompanied with a phase transition. Our experiments found that methscolopamine bromide—a compound chemically very similar to another thermosalient material, oxitropium bromide—exhibited crystal jumps during heating in the temperature range of 323–340 K. The same behavior was observed during cooling at a slightly lower temperature range of 313–303 K. Unlike other thermosalient solids reported so far, no phase transition was observed in this system. However, similar to other thermosalient materials, methscolopamine showed unusually large and anisotropic thermal expansion coefficients. This indicates that the thermosalient effect in this compound is caused by a different mechanism compared to all other reported materials, where it is governed by sharp and rapid phase transition. By contrast, thermosalient effect seems to be a continuous process in methscolopamine bromide. Full article

(This article belongs to the Special Issue Rietveld Refinement in the Characterization of Crystalline Materials)

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9 pages, 2795 KiB

Open AccessCommunication

Molecular Synchronization Enhances Molecular Interactions: An Explanatory Note of Pressure Effects

by Munenori Numata and Chisako Kanzaki

Crystals 2018, 8(7), 300; https://doi.org/10.3390/cryst8070300 - 20 Jul 2018

Cited by 3 | Viewed by 2741

Abstract

In this study, we investigated a unique aspect of the supramolecular polymerization of tetrakis (4-sulfonatophenyl) porphyrin (TPPS), a self-assembling porphyrin, under non-equilibrium conditions by subtracting the effects of back-pressure on its polymerization. We focused on the enhanced self-assembly abilities of TPPS under a [...] Read more.

In this study, we investigated a unique aspect of the supramolecular polymerization of tetrakis (4-sulfonatophenyl) porphyrin (TPPS), a self-assembling porphyrin, under non-equilibrium conditions by subtracting the effects of back-pressure on its polymerization. We focused on the enhanced self-assembly abilities of TPPS under a process of rapid proton diffusion in a microflow channel. Rapid protonation caused synchronization of many sets of protonation/deprotonation equilibria on the molecular scale, leading to the production of many sets of growing suparmolecular spices. Pressure effects in the microflow channel, which could potentially promote self-assembly of TPPS, were negligible, becoming predominant only when the system was in the synchronized state. Full article

(This article belongs to the Special Issue Microfluidic Platforms for Crystallography)

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13 pages, 5560 KiB

Open AccessArticle

Structural Transformations in Crystals Induced by Radiation and Pressure. Part 7. Molecular and Crystal Geometries as Factors Deciding about Photochemical Reactivity under Ambient and High Pressures

by Krzysztof Konieczny, Arkadiusz Ciesielski, Julia Bąkowicz, Tomasz Galica and Ilona Turowska-Tyrk

Crystals 2018, 8(7), 299; https://doi.org/10.3390/cryst8070299 - 20 Jul 2018

Cited by 5 | Viewed by 2927

Abstract

We studied the photochemical reactivity of salts of 4-(2,4,6-triisopropylbenzoyl)benzoic acid with propane-1,2-diamine (1), methanamine (2), cyclohexanamine (3), and morpholine (4), for compounds (1), (3), and (4) at 0.1 MPa [...] Read more.

We studied the photochemical reactivity of salts of 4-(2,4,6-triisopropylbenzoyl)benzoic acid with propane-1,2-diamine (1), methanamine (2), cyclohexanamine (3), and morpholine (4), for compounds (1), (3), and (4) at 0.1 MPa and for compounds (1) and (2) at 1.3 GPa and 1.0 GPa, respectively. The changes in the values of the unit cell parameters after UV irradiation and the values of the intramolecular geometrical parameters indicated the possibility of the occurrence of the Norrish–Yang reaction in the case of all the compounds. The analysis of the intramolecular geometry and free spaces revealed which o-isopropyl group takes part in the reaction. For (1), the same o-isopropyl group should be reactive at ambient and high pressures. In the case of (2), high pressure caused the phase transition from the space group I2/a with one molecule in the asymmetric unit cell to the space group P

\bar{1}

with two asymmetric molecules. The analysis of voids indicated that the Norrish–Yang reaction is less probable for one of the two molecules. For the other molecule, the intramolecular geometrical parameters showed that except for the Norrish–Yang reaction, the concurrent reaction leading to the formation of a five-membered ring can also proceed. In (3), both o-isopropyl groups are able to react; however, the bigger volume of a void near 2-isopropyl may be the factor determining the reactivity. For (4), only one o-isopropyl should be reactive. Full article

(This article belongs to the Special Issue Photocrystallography and Solid-State Structural Dynamics)

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15 pages, 4014 KiB

Open AccessArticle

Cryochemically Obtained Nanoforms of Antimicrobial Drug Substance Dioxidine and Their Physico-chemical and Structural Properties

by Tatyana I. Shabatina, Olga I. Vernaya, Vladimir P. Shabatin, Iuliia V. Evseeva, Michail Ya Melnikov, Andrew N. Fitch and Vladimir V. Chernyshev

Crystals 2018, 8(7), 298; https://doi.org/10.3390/cryst8070298 - 19 Jul 2018

Cited by 17 | Viewed by 4371

Abstract

Nanoforms of the antimicrobial drug substance 2,3-bis-(hydroxymethyl) quinoxaline-N,N′-dioxide with particles sizes between 50 and 300 nm were obtained by cryochemical modification of the initial pharmaceutical substance using a freeze-drying technique and were characterized by different physicochemical methods (FTIR, UV-Vis, ¹H-NMR, DSC, TG [...] Read more.

Nanoforms of the antimicrobial drug substance 2,3-bis-(hydroxymethyl) quinoxaline-N,N′-dioxide with particles sizes between 50 and 300 nm were obtained by cryochemical modification of the initial pharmaceutical substance using a freeze-drying technique and were characterized by different physicochemical methods (FTIR, UV-Vis, ¹H-NMR, DSC, TG and X-ray diffraction) and transmission electron microscopy (TEM). The data obtained from FTIR- and UV–Vis-spectroscopy confirmed the unaltered chemical structure of dioxidine molecules due to the cryochemical modification method. At the same time, X-ray diffraction and thermal analysis data show the change of the crystal structure compared to the parameters of the initial pharmaceutical dioxidine substance. A higher dissolution rate was revealed for cryomodified dioxidine nanoforms. The existence of three polymorphic crystal phases was established for cryomodified dioxidine samples possessed by some thermal activation processes: two anhydrous polymorphic phases, triclinic (T) and monoclinic (M), and one hydrated form (H). Full article

(This article belongs to the Section Crystal Engineering)

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7 pages, 2046 KiB

Open AccessArticle

Heavily Boron Doped Diamond Powder: Synthesis and Rietveld Refinement

by Igor P. Zibrov and Vladimir P. Filonenko

Crystals 2018, 8(7), 297; https://doi.org/10.3390/cryst8070297 - 19 Jul 2018

Cited by 12 | Viewed by 4436

Abstract

Boron-doped diamonds were synthesized by the reaction of an amorphous globular carbon powder (80%) with a powder of 1,7-di (oxymethyl)-M-carborane (20%) in a ‘toroid’-type high-pressure chamber at a pressure of 8.0 GPa and temperature of 1700 °C. The structure was refined by the [...] Read more.

Boron-doped diamonds were synthesized by the reaction of an amorphous globular carbon powder (80%) with a powder of 1,7-di (oxymethyl)-M-carborane (20%) in a ‘toroid’-type high-pressure chamber at a pressure of 8.0 GPa and temperature of 1700 °C. The structure was refined by the Rietveld method according to the X-ray powder diffraction data. It was shown that the unit cell parameters of these diamonds have two discrete quantities: around 3.570 Å for small concentrations of B (~1–1.5%) and around 3.578 Å for large concentrations of B (~2–3%). The concentration of the vacancies in the diamonds exceeds the concentration of boron atoms by 2–3 fold. This fact can play an important role in the formation of the structure and in determining the physical properties of diamonds. Full article

(This article belongs to the Special Issue Rietveld Refinement in the Characterization of Crystalline Materials)

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17 pages, 9307 KiB

Open AccessArticle

Deposition Technologies of High-Efficiency CIGS Solar Cells: Development of Two-Step and Co-Evaporation Processes

by Chia-Hua Huang, Wen-Jie Chuang, Chun-Ping Lin, Yueh-Lin Jan and Yu-Chiu Shih

Crystals 2018, 8(7), 296; https://doi.org/10.3390/cryst8070296 - 18 Jul 2018

Cited by 32 | Viewed by 6610

Abstract

The two-step process including the deposition of the metal precursors followed by heating the metal precursors in a vacuum environment of Se overpressure was employed for the preparation of Cu(In,Ga)Se₂ (CIGS) films. The CIGS films selenized at the relatively high Se flow [...] Read more.

The two-step process including the deposition of the metal precursors followed by heating the metal precursors in a vacuum environment of Se overpressure was employed for the preparation of Cu(In,Ga)Se₂ (CIGS) films. The CIGS films selenized at the relatively high Se flow rate of 25 Å/s exhibited improved surface morphologies. The correlations among the two-step process parameters, film properties, and cell performance were studied. With the given selenization conditions, the efficiency of 12.5% for the fabricated CIGS solar cells was achieved. The features of co-evaporation processes including the single-stage, bi-layer, and three-stage process were discussed. The characteristics of the co-evaporated CIGS solar cells were presented. Not only the surface morphologies but also the grading bandgap structures were crucial to the improvement of the open-circuit voltage of the CIGS solar cells. Efficiencies of over 17% for the co-evaporated CIGS solar cells have been achieved. Furthermore, the critical factors and the mechanisms governing the performance of the CIGS solar cells were addressed. Full article

(This article belongs to the Special Issue Selected Papers from Taiwan Association for Academic Innovation, TAAI 2018)

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11 pages, 2388 KiB

Open AccessArticle

Recrystallization and Production of Spherical Submicron Particles of Sulfasalazine Using a Supercritical Antisolvent Process

by Wei-Yi Wu and Chie-Shaan Su

Crystals 2018, 8(7), 295; https://doi.org/10.3390/cryst8070295 - 18 Jul 2018

Cited by 7 | Viewed by 5480

Abstract

In this study, the recrystallization and production of spherical submicron particles of sulfasalazine, an active pharmaceutical ingredient (API), were performed using the supercritical antisolvent (SAS) process, a nonconventional crystallization technique. Sulfasalazine was dissolved in tetrahydrofuran (THF), and supercritical carbon dioxide (CO₂) [...] Read more.

In this study, the recrystallization and production of spherical submicron particles of sulfasalazine, an active pharmaceutical ingredient (API), were performed using the supercritical antisolvent (SAS) process, a nonconventional crystallization technique. Sulfasalazine was dissolved in tetrahydrofuran (THF), and supercritical carbon dioxide (CO₂) served as the antisolvent. The effects of operating parameters on the SAS process, including the operating pressure, solution concentration, solution flowrate, CO₂ flowrate, and spraying nozzle diameter, at two operating temperatures were examined. The solid-state characteristics of sulfasalazine before and after the SAS process, including particle size, crystal habit, and crystal form, were analyzed using a scanning electron microscope (SEM), powder X-ray diffractometer (PXRD), and differential scanning calorimeter (DSC). A higher operating temperature, intermediate operating pressure, higher CO₂ flowrate, and lower solution flowrate are recommended to obtain spherical particles of sulfasalazine. The effects of the solution concentration and spraying nozzle diameter on the SAS process were negligible. Under optimal conditions, spherical sulfasalazine crystals with a mean size of 0.91 μm were generated, and this study demonstrated the feasibility for tuning the solid-state characteristics of API through the SAS process. Full article

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13 pages, 911 KiB

Open AccessArticle

Small Polaron Hopping in Fe:LiNbO₃ as a Function of Temperature and Composition

by Laura Vittadello, Marco Bazzan, Simon Messerschmidt and Mirco Imlau

Crystals 2018, 8(7), 294; https://doi.org/10.3390/cryst8070294 - 18 Jul 2018

Cited by 19 | Viewed by 4127

Abstract

Small-polaron hopping involved in charge transport in Fe-doped congruent lithium niobate is investigated as a function of temperature and composition by means of light-induced transient absorption spectroscopy. The relaxation dynamics of the light-induced polaron population is characterized by individual activation energies within different [...] Read more.

Small-polaron hopping involved in charge transport in Fe-doped congruent lithium niobate is investigated as a function of temperature and composition by means of light-induced transient absorption spectroscopy. The relaxation dynamics of the light-induced polaron population is characterized by individual activation energies within different temperature ranges. A numerical investigation carried out by Monte Carlo simulations reveals that these findings may be understood in terms of the varying abundance of the different types of hops that the polarons may perform among regular or defective lattice sites. The role of the temperature and of the sample composition on the distribution of the different hop types is thus explored for a wide range of parameters, allowing one to preview the charge transport properties for a given set of experimental conditions. Full article

(This article belongs to the Special Issue Lithium Niobate: Bulk Crystals, Composites, Thin Films and Nanocrystals)

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15 pages, 7225 KiB

Open AccessArticle

The Effect of Martensitic Phase Transformation Dilation on Microstructure, Strain–Stress and Mechanical Properties for Welding of High-Strength Steel

by Xizhang Chen, Pengfei Wang, Qiuhong Pan and Sanbao Lin

Crystals 2018, 8(7), 293; https://doi.org/10.3390/cryst8070293 - 15 Jul 2018

Cited by 10 | Viewed by 4192

Abstract

The application of low transformation temperature (LTT) wire can effectively reduce residual stress, without the need for preheating before welding and heat treatment after welding. The mechanism reduces the martensitic transformation temperature, allowing the martensite volume expansion to offset some or all of [...] Read more.

The application of low transformation temperature (LTT) wire can effectively reduce residual stress, without the need for preheating before welding and heat treatment after welding. The mechanism reduces the martensitic transformation temperature, allowing the martensite volume expansion to offset some or all of the heat-shrinking, resulting in reduced residual stress during the welding process. In this paper, commercial ER110S-G welding wire and LTT wire with chemical composition Cr10Ni8MnMoCuTiVB were developed to solve the problem of stress concentration. The microstructure of the LTT joint is mainly composed of martensite and a small amount of residual austenite, while the microstructure of the ER110S-G joint is mainly composed of ferrite and a small amount of granular bainite. The micro-hardness and tensile strength of the LTT joint is higher than that of ER110S-G joint; however, the impact toughness of the LTT joint is not as good as that of the ER110S-G joint. The martensitic phase transformation of LTT starts at 212 °C and finishes at around 50 °C, and the expansion caused by phase transition is about 0.48%, which is much higher than that of the base metal (0.15%) and ER110S-G (0.18%). The residual tensile stress at the weld zone of the ER110S-G joint is 175.5 MPa, while the residual compressive stress at the weld zone of LTT joint is −257.6 MPa. Full article

(This article belongs to the Special Issue Microstructures and Properties of Martensitic Materials)

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32 pages, 7120 KiB

Open AccessReview

Exploring the Topological Landscape Exhibited by Binary Zinc-triad 1,1-dithiolates

by Edward R.T. Tiekink

Crystals 2018, 8(7), 292; https://doi.org/10.3390/cryst8070292 - 14 Jul 2018

Cited by 41 | Viewed by 3843

Abstract

The crystal chemistry of the zinc-triad binary 1,1-dithiolates, that is, compounds of xanthate [⁻S₂COR], dithiophosphate [⁻S₂P(OR)₂], and dithiocarbamate [⁻S₂CNR₂] ligands, is reviewed. Owing to a wide range [...] Read more.

The crystal chemistry of the zinc-triad binary 1,1-dithiolates, that is, compounds of xanthate [⁻S₂COR], dithiophosphate [⁻S₂P(OR)₂], and dithiocarbamate [⁻S₂CNR₂] ligands, is reviewed. Owing to a wide range of coordination modes that can be adopted by 1,1-dithiolate anions, such as monodentate, chelating, μ₂-bridging, μ₃-bridging, etc., there exists a rich diversity in supramolecular assemblies for these compounds, including examples of zero-, one-, and two-dimensional architectures. While there are similarities in structural motifs across the series of 1,1-dithiolate ligands, specific architectures are sometimes found, depending on the metal centre and/or on the 1,1-dithiolate ligand. Further, an influence of steric bulk upon supramolecular aggregation is apparent. Thus, bulky R groups generally preclude the close approach of molecules in order to reduce steric hindrance and therefore, lead to lower dimensional aggregation patterns. The ligating ability of the 1,1-dithiolate ligands also proves crucial in determining the extent of supramolecular aggregation, in particular for dithiocarbamate species where the relatively greater chelating ability of this ligand reduces the Lewis acidity of the zinc-triad element, which thereby reduces its ability to significantly expand its coordination number. Often, the functionalisation of the organic substituents in the 1,1-dithiolate ligands, for example, by incorporating pyridyl groups, can lead to different supramolecular association patterns. Herein, the diverse assemblies of supramolecular architectures are classified and compared. In all, 27 structurally distinct motifs have been identified. Full article

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10 pages, 2756 KiB

Open AccessArticle

Multiscale Simulation of Surface Defects Influence Nanoindentation by a Quasi-Continuum Method

by Zhongli Zhang, Yushan Ni, Jinming Zhang, Can Wang, Kun Jiang and Xuedi Ren

Crystals 2018, 8(7), 291; https://doi.org/10.3390/cryst8070291 - 14 Jul 2018

Cited by 5 | Viewed by 3451

Abstract

Microscopic properties of nanocrystal aluminum thin film have been investigated using the quasicontinuum method in order to study the influence of surface defects in nanoindentation. Various distances between the surface defect and indenter have been taken into account. The results show that as [...] Read more.

Microscopic properties of nanocrystal aluminum thin film have been investigated using the quasicontinuum method in order to study the influence of surface defects in nanoindentation. Various distances between the surface defect and indenter have been taken into account. The results show that as the distance between the pit and indenter increases, the nanohardness increases in a wave pattern associated with a cycle of three atoms, which is closely related to the crystal structure of periodic atoms arrangement on {1 1 1} atomic close-packed planes of face-centered cubic metal; when the adjacent distance between the pit and indenter is more than 16 atomic spacing, there is almost no effect on nanohardness. In addition, the theoretical formula for the necessary load for elastic-to-plastic transition of Al film has been modified with the initial surface defect size, which may contribute to the investigation of material property with surface defects. Full article

(This article belongs to the Special Issue Selected Papers from "The 1st International Electronic Conference on Crystals")

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9 pages, 2230 KiB

Open AccessConference Report

Smeared Lattice Model as a Framework for Order to Disorder Transitions in 2D Systems

by Nadezhda L. Cherkas and Sergey L. Cherkas

Crystals 2018, 8(7), 290; https://doi.org/10.3390/cryst8070290 - 14 Jul 2018

Cited by 1 | Viewed by 3704

Abstract

Order to disorder transitions are important for two-dimensional (2D) objects such as oxide films with cellular porous structure, honeycomb, graphene, Bénard cells in liquid, and artificial systems consisting of colloid particles on a plane. For instance, solid films of porous alumina represent almost [...] Read more.

Order to disorder transitions are important for two-dimensional (2D) objects such as oxide films with cellular porous structure, honeycomb, graphene, Bénard cells in liquid, and artificial systems consisting of colloid particles on a plane. For instance, solid films of porous alumina represent almost regular crystalline structure. We show that in this case, the radial distribution function is well described by the smeared hexagonal lattice of the two-dimensional ideal crystal by inserting some amount of defects into the lattice.Another example is a system of hard disks in a plane, which illustrates order to disorder transitions. It is shown that the coincidence with the distribution function obtained by the solution of the Percus–Yevick equation is achieved by the smoothing of the square lattice and injecting the defects of the vacancy type into it. However, better approximation is reached when the lattice is a result of a mixture of the smoothed square and hexagonal lattices. Impurity of the hexagonal lattice is considerable at short distances. Dependencies of the lattice constants, smoothing widths, and contributions of the different type of the lattices on the filling parameter are found. The transition to order looks to be an increase of the hexagonal lattice fraction in the superposition of hexagonal and square lattices and a decrease of their smearing. Full article

(This article belongs to the Special Issue Selected Papers from "The 1st International Electronic Conference on Crystals")

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10 pages, 2295 KiB

Open AccessArticle

The Structure of Ferroselite, FeSe₂, at Pressures up to 46 GPa and Temperatures down to 50 K: A Single-Crystal Micro-Diffraction Analysis

by Barbara Lavina, Robert T. Downs and Stanislav Sinogeikin

Crystals 2018, 8(7), 289; https://doi.org/10.3390/cryst8070289 - 13 Jul 2018

Cited by 7 | Viewed by 5466

Abstract

We conducted an in situ crystal structure analysis of ferroselite at non-ambient conditions. The aim is to provide a solid ground to further the understanding of the properties of this material in a broad range of conditions. Ferroselite, marcasite-type FeSe₂, was [...] Read more.

We conducted an in situ crystal structure analysis of ferroselite at non-ambient conditions. The aim is to provide a solid ground to further the understanding of the properties of this material in a broad range of conditions. Ferroselite, marcasite-type FeSe₂, was studied under high pressures up to 46 GPa and low temperatures, down to 50 K using single-crystal microdiffraction techniques. High pressures and low temperatures were generated using a diamond anvil cell and a cryostat respectively. We found no evidences of structural instability in the explored P-T space. The deformation of the orthorhombic lattice is slightly anisotropic. As expected, the compressibility of the Se-Se dumbbell, the longer bond in the structure, is larger than that of the Fe-Se bonds. There are two octahedral Fe-Se bonds, the short bond, with multiplicity two, is slightly more compressible than the long bond, with multiplicity four; as a consequence the octahedral tetragonal compression slightly increases under pressure. We also achieved a robust structural analysis of ferroselite at low temperature in the diamond anvil cell. Structural changes upon temperature decrease are small but qualitatively similar to those produced by pressure. Full article

(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)

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12 pages, 2891 KiB

Open AccessArticle

Synthesis, Structure, and Properties of Coordination Polymers Based on 1,4-Bis((2-methyl-1H-imidazol-1-yl)methyl)benzene and Different Carboxylate Ligands

by Kang Liu, Yaowen Zhang, Liming Deng, Shaoshao Jiao, Zhenyu Xiao, Fan Cao and Lei Wang

Crystals 2018, 8(7), 288; https://doi.org/10.3390/cryst8070288 - 13 Jul 2018

Cited by 3 | Viewed by 4124

Abstract

Three novel coordination polymers, formulated as {[Zn(1,4-bmimb)(PhAA)₂]·H₂O}_n (1), [Cu(1,4-bmimb)_0.5(2,6-PyDC)]_n (2), and {[Cu(1,4-bmimb)_0.5(2-PAC)(HCOO)]·2H₂O}_n (3) (1,4-bmimb = 1,4-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene; PhAA = phenylacetic acid; 2,6-PyDC = [...] Read more.

Three novel coordination polymers, formulated as {[Zn(1,4-bmimb)(PhAA)₂]·H₂O}_n (1), [Cu(1,4-bmimb)_0.5(2,6-PyDC)]_n (2), and {[Cu(1,4-bmimb)_0.5(2-PAC)(HCOO)]·2H₂O}_n (3) (1,4-bmimb = 1,4-bis((2-methyl-1H-imidazol-1-yl)methyl)benzene; PhAA = phenylacetic acid; 2,6-PyDC = pyridine-2,6-dicarboxylic acid; 2-PAC = 2-pyrazinecarboxylic acid), were synthesized by the self-assembly of mixed ligands with Zn(II) and Cu(II) under solvothermal conditions and characterized by means of single-crystal X-ray diffraction, X-ray powder diffraction, infrared spectra, thermogravimetric analysis, fluorescence spectra and UV-vis absorption spectra. 1 is shown as a Z-shaped chain, which is formed by Zn²⁺, PhAA ligands, and 1,4-bmimb ligands, and is assembled into a 3D structure by hydrogen bonding and π···π interaction. Similarly, 2 displays a single chain, which is built by Cu²⁺, 2,6-PyDC ligands, and 1,4-bmimb ligands, and is assembled into a 3D structure by hydrogen bonding and π···π interaction. 3 possesses a 1D ladder structure, which is formed by Cu²⁺, 2,6-PyDC ligands, and 1,4-bmimb ligands, and is assembled into a 3D structure by hydrogen bonding. The luminescence properties (for 1) and UV-vis spectrum (for 2 and 3) were also studied and discussed. Full article

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13 pages, 5483 KiB

Open AccessArticle

The Effect of Skelp Thickness on Precipitate Size and Morphology for X70 Microalloyed Steel Using Rietveld Refinement (Quantitative X-ray Diffraction)

by Corentin Chatelier, J. Barry Wiskel, Douglas G. Ivey and Hani Henein

Crystals 2018, 8(7), 287; https://doi.org/10.3390/cryst8070287 - 12 Jul 2018

Cited by 3 | Viewed by 3096

Abstract

Precipitates in thin-walled (11 mm) and thick-walled X70 (17 mm) microalloyed X70 pipe steel are characterized using Rietveld refinement (a.k.a. quantitative X-ray diffraction (QXRD)), inductively coupled plasma mass spectrometry (ICP), and energy-dispersive X-ray spectroscopy (EDX) analyses. Rietveld refinement is done to quantify the [...] Read more.

Precipitates in thin-walled (11 mm) and thick-walled X70 (17 mm) microalloyed X70 pipe steel are characterized using Rietveld refinement (a.k.a. quantitative X-ray diffraction (QXRD)), inductively coupled plasma mass spectrometry (ICP), and energy-dispersive X-ray spectroscopy (EDX) analyses. Rietveld refinement is done to quantify the relative abundance, compositions, and size distribution of the precipitates. EDX and ICP analyses are undertaken to confirm Rietveld refinement analysis. The volume fraction of large precipitates (1 to 4 μm—mainly TiN rich precipitates) is determined to be twice as high in the thick-walled X70 steel (0.07%). Nano-sized precipitates (<20 nm) in the thin-walled steel exhibit a higher volume fraction (0.113%) than in the thick-walled steel (0.064%). The compositions of the nano-sized precipitates are similar for both steels. Full article

(This article belongs to the Special Issue Rietveld Refinement in the Characterization of Crystalline Materials)

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13 pages, 2895 KiB

Open AccessArticle

Development and In Vitro Evaluation of a Zerumbone Loaded Nanosuspension Drug Delivery System

by Shadab Md, Bradon C.M Kit, Sumeet Jagdish, Dexter J.P David, Manisha Pandey and Lipika Alok Chatterjee

Crystals 2018, 8(7), 286; https://doi.org/10.3390/cryst8070286 - 12 Jul 2018

Cited by 23 | Viewed by 4596

Abstract

Zerumbone extracted from the volatile oil of rhizomes available from the Zinigiber zerumbet has promising pharmacological activity. However, it has poor aqueous solubility and dissolution characteristics. To improve this, a nanosuspension formulation of zerumbone was developed. Nanosuspensions were formulated using high-pressure homogenization (HPH) [...] Read more.

Zerumbone extracted from the volatile oil of rhizomes available from the Zinigiber zerumbet has promising pharmacological activity. However, it has poor aqueous solubility and dissolution characteristics. To improve this, a nanosuspension formulation of zerumbone was developed. Nanosuspensions were formulated using high-pressure homogenization (HPH) with sodium dodecyl sulphate (SDS) and hydroxypropylmethylcellulose (HPMC) as stabilizers; the formulation was optimized and freeze dried. The optimized nanosuspension product was evaluated using an optical light microscope, photon correlation spectroscopy (PCS), polydispersity index, zeta potential, SEM, differential scanning calorimetry (DSC) and FT-IR. The physical stability of the nanosuspensions was evaluated for 30 days at 4 °C, 25 °C, and 37 °C. To validate the theoretical benefit of the increased surface area, we determined an in vitro saturation solubility and dissolution profile. The mean particle size, polydispersity index and zeta potential of the zerumbone nanosuspensions stabilized by SDS versus HPMC were found to be 211 ± 27 nm vs. 398 ± 3.5 nm, 0.39 ± 0.06 vs. 0.55 ± 0.004, and −30.86 ± 2.3 mV vs. −3.37 ± 0.002 mV, respectively. The in vitro saturation solubility and dissolution revealed improved solubility for the zerumbone nanosuspension. These results suggested that the nanosuspensionlization improves the saturation solubility and dissolution profile of zerumbone, which may facilitate its use as a therapeutic agent in the future. Full article

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20 pages, 2950 KiB

Open AccessArticle

Inhomogeneous Superconductivity in Organic and Related Superconductors

by Charles C. Agosta

Crystals 2018, 8(7), 285; https://doi.org/10.3390/cryst8070285 - 11 Jul 2018

Cited by 26 | Viewed by 5061

Abstract

Evidence of inhomogeneous superconductivity, in this case superconductivity with a spatially modulated superconducting order parameter, has now been found in many materials and by many measurement methods. Although the evidence is strong, it is circumstantial in the organic superconductors, scant in the pnictides, [...] Read more.

Evidence of inhomogeneous superconductivity, in this case superconductivity with a spatially modulated superconducting order parameter, has now been found in many materials and by many measurement methods. Although the evidence is strong, it is circumstantial in the organic superconductors, scant in the pnictides, and complex in the heavy Fermions. However, it is clear some form of exotic superconductivity exists at high fields and low temperatures in many electronically anisotropic superconductors. The evidence is reviewed in this article, and examples of similar measurements are compared across different families of superconductors. An effort is made to find a consistent way to measure the superconducting energy gap across all materials, and use this value to predict the Clogston–Chandrasakhar paramagnetic limit H_p. Methods for predicting the existence of inhomogeneous superconductivity are shown to work for the organic superconductors, and then used to suggest new materials to study. Full article

(This article belongs to the Special Issue Advances in Organic Conductors and Superconductors)

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8 pages, 1833 KiB

Open AccessCommunication

Over-Expression, Secondary Structure Characterization, and Preliminary X-ray Crystallographic Analysis of Xenopus tropicalis Ependymin

by Jeong Kuk Park, Yeo Won Sim and SangYoun Park

Crystals 2018, 8(7), 284; https://doi.org/10.3390/cryst8070284 - 11 Jul 2018

Cited by 4 | Viewed by 2965

Abstract

The gene encoding frog (Xenopus tropicalis) ependymin without the signaling sequence was gene-synthesized, and the protein successfully over-expressed in ~mg quantities adequate for crystallization using insect cell expression. Circular dichroism (CD) analysis of the protein purified with >95% homogeneity indicated that [...] Read more.

The gene encoding frog (Xenopus tropicalis) ependymin without the signaling sequence was gene-synthesized, and the protein successfully over-expressed in ~mg quantities adequate for crystallization using insect cell expression. Circular dichroism (CD) analysis of the protein purified with >95% homogeneity indicated that ependymin contains both α-helix and β-strand among the secondary structure elements. The protein was further crystallized using polyethylene glycol 8000 as the precipitating reagent, and X-ray diffraction data were collected to 2.7 Å resolution under cryo-condition at a synchrotron facility. The crystal belongs to a hexagonal space group P6₁22 (or P6₅22) having unit cell parameters of a = b = 61.05 Å, c = 234.33 Å. Matthews coefficient analysis indicated a crystal volume per protein mass (V_M) of 2.76 Å³ Da⁻¹ and 55.4% solvent content in the crystal when the calculated molecular mass of the protein only was used. However, the apparent SDS-PAGE molecular mass of ~33 kDa (likely resulting from N-glycosylation) suggested V_M of 1.90 Å³ Da⁻¹ and 35.4% solvent content instead. In both cases, the asymmetric unit of the crystal likely contains only one subunit of the protein. Full article

(This article belongs to the Special Issue Biological Crystallization)

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14 pages, 3589 KiB

Open AccessReview

Structural Reasons for the Nonlinear Optical Properties of KTP Family Single Crystals

by Nataliya E. Novikova, Nataliya I. Sorokina, Igor A. Verin, Olga A. Alekseeva, Ekaterina I. Orlova, Valentina I. Voronkova and Michael Tseitlin

Crystals 2018, 8(7), 283; https://doi.org/10.3390/cryst8070283 - 10 Jul 2018

Cited by 27 | Viewed by 4711

Abstract

A brief review focuses on studies into the structural reasons for the nonlinear optical properties of crystals of the potassium titanyl phosphate family, performed at the Shubnikov Institute of Crystallography. Accurate X-ray diffraction data are discussed, providing evidence that the optical susceptibility of [...] Read more.

A brief review focuses on studies into the structural reasons for the nonlinear optical properties of crystals of the potassium titanyl phosphate family, performed at the Shubnikov Institute of Crystallography. Accurate X-ray diffraction data are discussed, providing evidence that the optical susceptibility of crystals is related not only to the alternation of long and short Ti–O bonds in the chains of TiO₆ octahedra, but to the geometry of tetrahedral anions and the alkaline cation arrangement in the structure channels, as well. The contribution of each of the three structural components depends on the crystal composition. Full article

(This article belongs to the Special Issue KTP Crystal for Nonlinear Optical and Electrooptic Applications)

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11 pages, 2171 KiB

Open AccessArticle

Constitutive Modelling and Hot Workability Analysis by Microstructure Examination of GH4169 Alloy

by Rongchuang Chen, Zhizhen Zheng, Jianjun Li and Fei Feng

Crystals 2018, 8(7), 282; https://doi.org/10.3390/cryst8070282 - 9 Jul 2018

Cited by 15 | Viewed by 3489

Abstract

The relationships between hot deformation parameters and flow behaviour have attracted many researchers’ attention for the past few decades, whilst precise constitutive modelling of GH4169 remained a problem, which seriously affected the process and microstructure control of alloys. In this work, a modified [...] Read more.

The relationships between hot deformation parameters and flow behaviour have attracted many researchers’ attention for the past few decades, whilst precise constitutive modelling of GH4169 remained a problem, which seriously affected the process and microstructure control of alloys. In this work, a modified Arrhenius type model was introduced to describe the flow stresses of various compression conditions. The model showed high precision in flow stress prediction. In order to facilitate workability evaluation for engineering applications, the hot processing maps were established at the strain of 0.4~0.6. The processing maps revealed an instability domain at 900~950 °C and 0.1~1 s⁻¹, a high dissipation efficiency domain at 1060~1100 °C and 0.001~0.01 s⁻¹, and a stable deformation domain for the rest of processing parameters. Microstructures of each domain were observed via optical microscope (OM) and electron backscattered diffraction (EBSD). The intriguing finding was that the microstructures morphology agreed well with the descriptions in “discontinuous mechanism”, and incompletely recrystallized microstructures were found in the instability domain. Fully recrystallized microstructures were found in the stable deformation domain, and grain coarsen in the high dissipation efficiency domain. Optimal hot working conditions were suggested based on the microstructure analysis. This investigation contributed to a comprehensive understanding of the workability of GH4169. Full article

(This article belongs to the Special Issue Recrystallization of Metallic Materials )

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8 pages, 2350 KiB

Open AccessArticle

The Role of Chirality and Helicity between d- and l-Valine Optical Lattices

by Jingjing Li, Wenqing Wang and Yan Gong

Crystals 2018, 8(7), 281; https://doi.org/10.3390/cryst8070281 - 5 Jul 2018

Viewed by 2901

Abstract

With the aim to investigate the role of chirality and helicity between d- and l-valine crystal lattices under Debye temperature 2–20 K, magnetic field dependence of zero-field and 1, 3 and 5 Tesla on the heat capacity were measured. The heat [...] Read more.

With the aim to investigate the role of chirality and helicity between d- and l-valine crystal lattices under Debye temperature 2–20 K, magnetic field dependence of zero-field and 1, 3 and 5 Tesla on the heat capacity were measured. The heat capacities of d- and l-valine crystals were plotted as C_p vs. T, C_p vs. lnT, C_p/T³ vs. T in the measured temperature. The four C_p/T³ vs. T curves show a split between d- and l-valine from 2 K to 12 K (T <<

Θ_{D}

) which is due to the strength of magnetic fields. It is absent from 12 K to 20 K, which indicates the Schottky anomaly. The Bose–Einstein peak of the (e-p) condensation temperature is 11.20, 11.32, 11.44, 11.46 K for d-valine, and 11.49, 11.59, 11.73, 11.70 K for l-valine, respectively. This finding leads to a zero-field splitting of a broad maximum associated with the Schottky anomaly below the temperature of 12 K which is demonstrated by (e-p) Bose–Einstein condensation through the hydrogen of peptide bond in the alpha helix at zero momentum space onto d- and l-valine optical lattices. Full article

(This article belongs to the Special Issue Crystal Structures of Amino Acids and Peptides)

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20 pages, 13880 KiB

Open AccessReview

The Effects of Ultrasound on Crystals: Sonocrystallization and Sonofragmentation

by Hyo Na Kim and Kenneth S. Suslick

Crystals 2018, 8(7), 280; https://doi.org/10.3390/cryst8070280 - 4 Jul 2018

Cited by 95 | Viewed by 14529

Abstract

When ultrasound is applied to a solution for crystallization, it can affect the properties of the crystalline products significantly. Ultrasonic irradiation decreases the induction time and metastable zone and increases the nucleation rate. Due to these effects, it generally yields smaller crystals with [...] Read more.

When ultrasound is applied to a solution for crystallization, it can affect the properties of the crystalline products significantly. Ultrasonic irradiation decreases the induction time and metastable zone and increases the nucleation rate. Due to these effects, it generally yields smaller crystals with a narrower size distribution when compared with conventional crystallizations. Also, ultrasonic irradiation can cause fragmentation of existing crystals which is caused by crystal collisions or sonofragmentation. The effect of various experimental parameters and empirical products of sonocrystallization have been reported, but the mechanisms of sonocrystallization and sonofragmentation have not been confirmed clearly. In this review, we build upon previous studies and highlight the effects of ultrasound on the crystallization of organic molecules. In addition, recent work on sonofragmentation of molecular and ionic crystals is discussed. Full article

(This article belongs to the Special Issue Advances in Ultrasound Stimulated Crystallization)

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12 pages, 12254 KiB

Open AccessArticle

Effect of Substrate Surface on Deposition of AlGaN: A Molecular Dynamics Simulation

by Libin Zhang, Han Yan, Guo Zhu, Sheng Liu, Zhiyin Gan and Zili Zhang

Crystals 2018, 8(7), 279; https://doi.org/10.3390/cryst8070279 - 3 Jul 2018

Cited by 13 | Viewed by 5366

Abstract

The growth of AlGaN has been extensively studied, but corresponding research related to the effect of AlN substrate surface has rarely been reported in literature. In this article, the effects of AlN substrate surface on deposition of AlGaN films were investigated by molecular [...] Read more.

The growth of AlGaN has been extensively studied, but corresponding research related to the effect of AlN substrate surface has rarely been reported in literature. In this article, the effects of AlN substrate surface on deposition of AlGaN films were investigated by molecular dynamics (MD) simulations. (0001) Al-terminated and

(000 \bar{1})

N-terminated AlN were considered as substrates. The quality of surface morphology and atomic scale structure of deposited AlGaN film are discussed in detail. The results show that the surface morphology and crystal quality of AlGaN film grown on (0001) Al-terminated AlN surface are better than for that grown on

(000 \bar{1})

N-terminated AlN surface under various growing temperatures and Al/Ga injection ratios between Al and Ga. This can be attributed to the higher mobility of Al and Ga adatoms on the (0001) Al-terminated AlN surface. These findings can provide guidance for the preparation of high-quality AlGaN thin films on AlN substrate. Full article

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9 pages, 2165 KiB

Open AccessArticle

Thermal Conductivity of an AZ31 Sheet after Accumulative Roll Bonding

by Zuzanka Trojanová, Kristýna Halmešová, Zdeněk Drozd, Vladimír Šíma, Pavel Lukáč, Ján Džugan and Peter Minárik

Crystals 2018, 8(7), 278; https://doi.org/10.3390/cryst8070278 - 2 Jul 2018

Cited by 11 | Viewed by 3667

Abstract

Accumulative roll bonding (ARB) is one of the methods of severe plastic deformation which is relevant for industrial production of sheets. While mechanical properties of several magnesium alloys subjected to the ARB process have been studied, the physical properties have been reported only [...] Read more.

Accumulative roll bonding (ARB) is one of the methods of severe plastic deformation which is relevant for industrial production of sheets. While mechanical properties of several magnesium alloys subjected to the ARB process have been studied, the physical properties have been reported only for some magnesium alloys. These properties are influenced by the texture developed during the ARB process and the temperature load. In the presented contribution, we studied thermal conductivity of an AZ31 magnesium alloy after one and two passes through the rolling mill. Thermal diffusivity was measured with the laser-flash method in the temperature range between 20 and 350 °C. Thermal conductivity depends on the number of rolling passes. The microstructure and texture of sheets are significant factors influencing thermal properties. Full article

(This article belongs to the Special Issue Microstructure and Physical Properties of Magnesium Alloys and Composites)

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10 pages, 11479 KiB

Open AccessArticle

An Improved Organic Solar Cell Lumped-Parameter Equivalent Circuit Model

by Chuanzhong Xu, Fei Yu, Wei Lin and Gongyi Huang

Crystals 2018, 8(7), 277; https://doi.org/10.3390/cryst8070277 - 30 Jun 2018

Cited by 8 | Viewed by 3497

Abstract

An improved lumped-parameter equivalent circuit model is proposed to describe S-shaped I–V characteristics of organic solar cells (OSCs). This model originates but differs from Mazhari’s model. As a minor but important modification, a shunt resistance is added to Mazhari’s model to increase the [...] Read more.

An improved lumped-parameter equivalent circuit model is proposed to describe S-shaped I–V characteristics of organic solar cells (OSCs). This model originates but differs from Mazhari’s model. As a minor but important modification, a shunt resistance is added to Mazhari’s model to increase the accuracy of simulating the S-shaped kink in the third quadrant. Subsequently, we present a terminal current-voltage equation set and derive an analytical solution to the improved model. Furthermore, we verify the analytical solution to our model by using the least square method and validate our model by using the experimental I–V curves examined from OSCs. Compared with Mazhari’s model, our model has greater accuracy in interpreting the S-shaped kink with linear-like rise in the third quadrant. As a result, our improved model is suitable to explain the S-shaped I–V characteristics of organic solar cells in the whole operational region, especially for the S-shaped kink in the third quadrant. Full article

(This article belongs to the Special Issue Selected Papers from Taiwan Association for Academic Innovation, TAAI 2018)

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17 pages, 3550 KiB

Open AccessArticle

Ammoniates of Zintl Phases: Similarities and Differences of Binary Phases A₄E₄ and Their Corresponding Solvates

by Corinna Lorenz, Stefanie Gärtner and Nikolaus Korber

Crystals 2018, 8(7), 276; https://doi.org/10.3390/cryst8070276 - 29 Jun 2018

Cited by 14 | Viewed by 4452

Abstract

The combination of electropositive alkali metals A (A = Na-Cs) and group 14 elements E (E = Si-Pb) in a stoichiometric ratio of 1:1 in solid state reactions results in the formation of polyanionic salts, which belong to a class of intermetallics for [...] Read more.

The combination of electropositive alkali metals A (A = Na-Cs) and group 14 elements E (E = Si-Pb) in a stoichiometric ratio of 1:1 in solid state reactions results in the formation of polyanionic salts, which belong to a class of intermetallics for which the term Zintl compounds is used. Crystal structure analysis of these intermetallic phases proved the presence of tetrahedral tetrelide tetraanions [E₄]⁴⁻ precast in solid state, and coulombic interactions account for the formation of a dense, three-dimensional cation-anion network. In addition, it has been shown that [E₄]⁴⁻ polyanions are also present in solutions of liquid ammonia prepared via different synthetic routes. From these solutions crystallize ammoniates of the alkali metal tetrahedranides, which contain ammonia molecules of crystallization, and which can be characterized by X-ray crystallography despite their low thermal stability. The question to be answered is about the structural relations between the analogous compounds in solid state vs. solvate structures, which all include the tetrahedral [E₄]⁴⁻ anions. We here investigate the similarities and differences regarding the coordination spheres of these anions and the resulting cation-anion network. The reported solvates Na₄Sn₄·13NH₃, Rb₄Sn₄·2NH₃, Cs₄Sn₄·2NH₃, Rb₄Pb₄·2NH₃ as well as the up to now unpublished crystal structures of the new compounds Cs₄Si₄·7NH₃, Cs₄Ge₄·9NH₃, [Li(NH₃)₄]₄Sn₄·4NH₃, Na₄Sn₄·11.5NH₃ and Cs₄Pb₄·5NH₃ are considered for comparisons. Additionally, the influence of the presence of another anion on the overall crystal structure is discussed by using the example of a hydroxide co-crystal which was observed in the new compound K_4.5Sn₄(OH)_0.5∙1.75 NH₃. Full article

(This article belongs to the Special Issue Compounds with Polar Metallic Bonding)

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12 pages, 4049 KiB

Open AccessArticle

Quasicrystalline Ordering in Thin Liquid Crystal Films

by Jayasri Dontabhaktuni, Miha Ravnik and Slobodan Zumer

Crystals 2018, 8(7), 275; https://doi.org/10.3390/cryst8070275 - 29 Jun 2018

Cited by 5 | Viewed by 4813

Abstract

Quasicrystalline ordering was first observed in synthetic multi-component metallic alloys. These solid state materials exhibit quasicrystalline atomic ordering at nanometer length scales. Softmatter systems are another class of versatile materials that can exhibit quasicrystalline ordering across supra-nanometer (>10 nm) to supra-micrometer (>10

μ

[...] Read more.

Quasicrystalline ordering was first observed in synthetic multi-component metallic alloys. These solid state materials exhibit quasicrystalline atomic ordering at nanometer length scales. Softmatter systems are another class of versatile materials that can exhibit quasicrystalline ordering across supra-nanometer (>10 nm) to supra-micrometer (>10

μ

m) length scales as recently observed in materials like-supramolecular dendritic molecules, ABC star polymers, binary nanoparticle systems and block co-polymers in condensed matter systems. The underlying mechanism in most of these soft quasicrystals seems to be the presence of two or more length scales in the system. Another class of development in self-assembled quasicrystals in softmatter is being observed in low molecular weight chiral and achiral nematic liquid crystals. Liquid crystal forms an efficient matrix for self- and directed-assemblies of colloidal structures where surface and geometry-tuning the particles in nematic liquid crystals gives rise to complex inter-particle interactions while the long-range order results in self-assembled structures of higher order rotational symmetries. Furthermore, there has also been attempts to generate colloidal quasicrystalline defect structures by directing the assemblies using multiple and single beam lasing techniques. In the present article, we will review self- and assisted-assembly of quasicrystalline structures in nematic liquid crystals (both chiral and achiral) and discuss the underlying mechanisms. Full article

(This article belongs to the Special Issue Structure and Properties of Quasicrystalline Materials)

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11 pages, 2273 KiB

Open AccessArticle

A Study of the Crystal Structure and Hydrogen Bonding of 3-Trifluoroacetyloxime Substituted 7-Acetamido-2-aryl-5-bromoindoles

by Malose J. Mphahlele

Crystals 2018, 8(7), 274; https://doi.org/10.3390/cryst8070274 - 29 Jun 2018

Cited by 1 | Viewed by 3075

Abstract

The 7-acetyl-2-aryl-5-bromo-3-(trifluoroacetyl)indoles 1a-d were reacted with hydroxylamine hydrochloride (2.2 equiv.) in the presence of pyridine in ethanol under reflux to afford the corresponding diketo oxime derivatives 2a-d. Beckmann rearrangement of the latter with trifluoroacetic acid under reflux afforded [...] Read more.

The 7-acetyl-2-aryl-5-bromo-3-(trifluoroacetyl)indoles 1a-d were reacted with hydroxylamine hydrochloride (2.2 equiv.) in the presence of pyridine in ethanol under reflux to afford the corresponding diketo oxime derivatives 2a-d. Beckmann rearrangement of the latter with trifluoroacetic acid under reflux afforded the corresponding 7-acetamido-2-aryl-5-bromo-3-(trifluoroacetyloxime)indoles 3a-d. The structures of the prepared compounds were characterized using a combination of NMR (¹H & ¹³C), IR, and mass spectrometric techniques. The molecular structure of the 3-trifluoroacetyloxime substituted 7-acetamido-2-aryl-5-bromoindoles was unambiguously confirmed by the single crystal X-ray diffraction data of 3d. Structural studies of 3d in the solid state by X-ray crystallography provided evidence of hydrogen bonding networks and π-stacking of the indole moiety. Compound 3d was crystallized in the trigonal space group R-3:H with unit cell dimensions a = 25.1614(13), b = 25.1614(13), c = 17.3032(9) Å, α = β = 90°, γ = 120°, V = 9486.9(11) Å³, Z = 6. The density functional theory (DFT) structural parameters (bond lengths, bond angles, and torsion angles) of the optimized geometry calculated using the B3LYP/6-311G basis set were found to compare favourably with those of the X-ray crystal structure. Full article

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Crystals, Volume 8, Issue 7 (July 2018) – 45 articles

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