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Crystals, Volume 7, Issue 10 (October 2017)

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Cover Story Quasicrystal dynamics and growth are guided by the non-local empires—tiles forced by certain local [...] Read more.
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Editorial

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Open AccessEditorial Crystals 2017 Best Paper Award
Crystals 2017, 7(10), 283; doi:10.3390/cryst7100283
Received: 17 September 2017 / Revised: 19 September 2017 / Accepted: 19 September 2017 / Published: 21 September 2017
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Abstract
Crystals is instituting the Best Paper Award to recognize the outstanding papers published in the journal. We are pleased to announce the “Crystals Best Paper Award” for 2017. [...] Full article

Research

Jump to: Editorial, Review, Other

Open AccessArticle Effect of Ionic Liquids on the Separation of Sucrose Crystals from a Natural Product Using Crystallization Techniques
Crystals 2017, 7(10), 284; doi:10.3390/cryst7100284
Received: 26 August 2017 / Revised: 18 September 2017 / Accepted: 20 September 2017 / Published: 23 September 2017
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Abstract
The present work aims to investigate the applicability of ionic liquids (ILs) for natural ingredient crystallization. First, the medicinal plant, namely Angelica gigas Nakai, was extracted using methanol (MeOH) as a solvent. Afterwards, ILs 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF4), 1-butyl-3-methylimidazolium hexafluorophosphate (BMImPF6
[...] Read more.
The present work aims to investigate the applicability of ionic liquids (ILs) for natural ingredient crystallization. First, the medicinal plant, namely Angelica gigas Nakai, was extracted using methanol (MeOH) as a solvent. Afterwards, ILs 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF4), 1-butyl-3-methylimidazolium hexafluorophosphate (BMImPF6), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMImTFSI), 1-allyl-3-ethylim idazolium tetrafluoroborate (AEImBF4), and 1,3-diallyl imidazolium tetrafluoroborate (AAImBF4), in three ratios of 1:1, 1:2, and 1:3 (extraction solution/ILs (v/v)) were used as an anti-solvent to induce crystallization. Crystals were obtained within 8 h and were then identified to be pure crystals of sucrose through nuclear magnetic resonance (1H-NMR) analysis. Moreover, the single-crystal X-ray diffraction (SXD) analysis revealed all recovered crystals have an identical crystal structure and the morphology was monitored using a video microscope. With the application of BMImBF4 and BMImPF6, transformation of sucrose crystal morphology from an elongated hexagon shape to an elongated rectangular shape was observed with respect to the respective concentration increase. Here, all crystals precipitated from BMImBF4 and BMImPF6 were found to possess identical PXRD patterns. However, when BMImTFSI was employed, small rectangular crystals attached to the larger rectangular-shaped crystals due to secondary nucleation and shapeless amorphous forms were observed according to the alteration in the solution to ILs ratio. Accordingly, the ability of ILs as a relevant anti-solvent for the selective crystallization of a single compound from a natural product was assessed through the study. Furthermore, the applicability of ILs as crystal engineering solvents are expected to modify both the solid state and the crystal morphology of natural compounds, which can influence drug manufacturability, dissolution rate, and bioavailability. Full article
(This article belongs to the Special Issue Ionic Liquids in Drug Delivery)
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Open AccessArticle Electro-optical Effect of Gold Nanoparticle Dispersed in Nematic Liquid Crystals
Crystals 2017, 7(10), 287; doi:10.3390/cryst7100287
Received: 13 July 2017 / Revised: 21 September 2017 / Accepted: 22 September 2017 / Published: 23 September 2017
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Abstract
The electro-optical performance of nematic liquid crystals (NLCs) dispersed with gold nanoparticles (GNPs) was investigated in this study. The addition of a small amount of GNP dopant decreased the threshold voltage for LC reorientation due to the decreased elastic constant and increased dielectric
[...] Read more.
The electro-optical performance of nematic liquid crystals (NLCs) dispersed with gold nanoparticles (GNPs) was investigated in this study. The addition of a small amount of GNP dopant decreased the threshold voltage for LC reorientation due to the decreased elastic constant and increased dielectric anisotropy of the LC mixture. The response time of the LC cell was decreased with the addition of tiny amounts of GNPs because of decrease in rotational viscosity of LCs. The doped GNPs also shorten LC reorientation angle during voltage switching, further decreasing the response time of the LC cell. The addition of high amounts of GNPs slowed down the response time of the LC cell, because excess GNPs aggregated and formed networks in the cell, thus disturbing LC alignment and hindering LC reorientation. The measured dielectric spectra of the GNP-LC mixture revealed that the addition of GNPs decreased the relaxation time constant of the LCs. This result confirmed that the GNP dopant decreased the rotational viscosity and elastic constant of the LCs. Full article
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Open AccessFeature PaperArticle In Silico Prediction of Growth and Dissolution Rates for Organic Molecular Crystals: A Multiscale Approach
Crystals 2017, 7(10), 288; doi:10.3390/cryst7100288
Received: 27 June 2017 / Revised: 14 September 2017 / Accepted: 18 September 2017 / Published: 25 September 2017
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Abstract
Solution crystallization and dissolution are of fundamental importance to science and industry alike and are key processes in the production of many pharmaceutical products, special chemicals, and so forth. The ability to predict crystal growth and dissolution rates from theory and simulation alone
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Solution crystallization and dissolution are of fundamental importance to science and industry alike and are key processes in the production of many pharmaceutical products, special chemicals, and so forth. The ability to predict crystal growth and dissolution rates from theory and simulation alone would be of a great benefit to science and industry but is greatly hindered by the molecular nature of the phenomenon. To study crystal growth or dissolution one needs a multiscale simulation approach, in which molecular-level behavior is used to parametrize methods capable of simulating up to the microscale and beyond, where the theoretical results would be industrially relevant and easily comparable to experimental results. Here, we review the recent progress made by our group in the elaboration of such multiscale approach for the prediction of growth and dissolution rates for organic crystals on the basis of molecular structure only and highlight the challenges and future directions of methodic development. Full article
(This article belongs to the Special Issue Advances in Computer Simulation Studies on Crystal Growth)
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Open AccessArticle Microstructural Feature and Magnetocaloric Effect of Mn50Ni40.5In9.5 Melt-Spun Ribbons
Crystals 2017, 7(10), 289; doi:10.3390/cryst7100289
Received: 24 August 2017 / Revised: 14 September 2017 / Accepted: 21 September 2017 / Published: 25 September 2017
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Abstract
The microstructure and magnetocaloric properties of the melt-spun and annealed Mn50Ni40.5In9.5 ribbons were studied. It is shown that the post-annealing results in a considerable increase of the grain size for the initial austenite, where the columnar-shaped austenite grains
[...] Read more.
The microstructure and magnetocaloric properties of the melt-spun and annealed Mn50Ni40.5In9.5 ribbons were studied. It is shown that the post-annealing results in a considerable increase of the grain size for the initial austenite, where the columnar-shaped austenite grains almost run through the whole ribbon. Both the melt-spun and annealed ribbons consist of the mixture of austenite and martensite at room temperature, where a 8-layered modulated (8M) martensite structure was identified through selected area electron diffraction (SAED). Further High-angle Annular Dark-field (HAADF) characterizations reveal that the modulation period of 8M martensite is not homogeneous in one martensite plate. Due to strong magneto-structural coupling, the inverse martensitic transformation from a weak magnetic martensite to a strong magnetic austenite can be induced by the magnetic field, resulting in the inverse magnetocaloric effect around room temperature. For a field change of 5 T, the magnetic entropy change ΔSM of 3.7 J·kg−1·K−1 and 6.1 J·kg−1·K−1, and the effective refrigerant capacity RCeff of 52.91 J·kg−1 and 99.08 J·kg−1 were obtained for melt-spun and annealed ribbons, respectively. The improvement of the magnetocaloric properties after annealing should be attributed to the enhanced atomic ordering and magnetization difference between two phases, as well as the reduced hysteresis loss. In addition, both the melt-spun and annealed ribbons can work at a relatively wide temperature range, i.e., δTFWHM = 34 K for melt-spun ribbons and δTFWHM = 28 K for annealed ribbons. Full article
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Open AccessCommunication Synthesis and X-ray Crystal Structure of N’-Cyano-N,N’-dimethyl-4-nitrobenzohydrazide
Crystals 2017, 7(10), 290; doi:10.3390/cryst7100290
Received: 29 August 2017 / Revised: 18 September 2017 / Accepted: 19 September 2017 / Published: 26 September 2017
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Abstract
Using a two-step procedure, N’-cyano-N,N’-dimethyl-4-nitrobenzohydrazide was synthesized. The structure was established using single crystal X-ray diffraction. It crystalized in the orthorhombic space group P212121 where a = 8.1974(6), b = 10.6696(7), and
[...] Read more.
Using a two-step procedure, N’-cyano-N,N’-dimethyl-4-nitrobenzohydrazide was synthesized. The structure was established using single crystal X-ray diffraction. It crystalized in the orthorhombic space group P212121 where a = 8.1974(6), b = 10.6696(7), and c = 12.9766(8) Å. The first reported crystal structure of an acyclic cyanohydrazide is discussed with a focus on the geometry of the hydrazide moiety, but intermolecular contacts in the crystal are also considered. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle Solvent-Dependent Thermoelectric Properties of PTB7 and Effect of 1,8-Diiodooctane Additive
Crystals 2017, 7(10), 292; doi:10.3390/cryst7100292
Received: 19 August 2017 / Revised: 17 September 2017 / Accepted: 26 September 2017 / Published: 29 September 2017
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Abstract
Conjugated polymers are considered for application in thermoelectric energy conversion due to their low thermal conductivity, low weight, non-toxicity, and ease of fabrication, which promises low manufacturing costs. Here, an investigation of the thermoelectric properties of poly({4,8-bis[(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b′] dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl) carbonyl]thieno[3,4-b] thiophenediyl}), commonly known
[...] Read more.
Conjugated polymers are considered for application in thermoelectric energy conversion due to their low thermal conductivity, low weight, non-toxicity, and ease of fabrication, which promises low manufacturing costs. Here, an investigation of the thermoelectric properties of poly({4,8-bis[(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b′] dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl) carbonyl]thieno[3,4-b] thiophenediyl}), commonly known as PTB7 conjugated polymer, is reported. Samples were prepared from solutions of PTB7 in three different solvents: chlorobenzene, 1,2-dichlorobenzene, and 1,2,4-trichlorobenzene, with and without 1,8-diiodooctane (DIO) additive. In order to characterize their thermoelectric properties, the electrical conductivity and the Seebeck coefficient were measured. We found that, by increasing the boiling point of the solvent, both the electrical conductivity and the Seebeck coefficient of the PTB7 samples were simultaneously improved. We believe that the increase in mobility is responsible for solvent-dependent thermoelectric properties of the PTB7 samples. However, the addition of DIO changes the observed trend. Only the sample prepared from 1,2,4-trichlorobenzene showed a higher electrical conductivity and Seebeck coefficient and, as a consequence, improved power factor in comparison to the samples prepared from chlorobenzene and 1,2-dichlorobenzene. Full article
(This article belongs to the Special Issue Materials Processing and Crystal Growth for Thermoelectrics)
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Open AccessArticle Atomistic Studies of Nanoindentation—A Review of Recent Advances
Crystals 2017, 7(10), 293; doi:10.3390/cryst7100293
Received: 12 September 2017 / Revised: 25 September 2017 / Accepted: 26 September 2017 / Published: 29 September 2017
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Abstract
This review covers areas where our understanding of the mechanisms underlying nanoindentation has been increased by atomistic studies of the nanoindentation process. While such studies have been performed now for more than 20 years, recent investigations have demonstrated that the peculiar features of
[...] Read more.
This review covers areas where our understanding of the mechanisms underlying nanoindentation has been increased by atomistic studies of the nanoindentation process. While such studies have been performed now for more than 20 years, recent investigations have demonstrated that the peculiar features of nanoplasticity generated during indentation can be analyzed in considerable detail by this technique. Topics covered include: nucleation of dislocations in ideal crystals, effect of surface orientation, effect of crystallography (fcc, bcc, hcp), effect of surface and bulk damage on plasticity, nanocrystalline samples, and multiple (sequential) indentation. In addition we discuss related features, such as the influence of tip geometry on the indentation and the role of adhesive forces, and how pre-existing plasticity affects nanoindentation. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessArticle The Effect of Ultrasound on the Crystallisation of Paracetamol in the Presence of Structurally Similar Impurities
Crystals 2017, 7(10), 294; doi:10.3390/cryst7100294
Received: 17 August 2017 / Revised: 14 September 2017 / Accepted: 26 September 2017 / Published: 30 September 2017
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Abstract
Sono-crystallisation has been used to enhance crystalline product quality particularly in terms of purity, particle size and size distribution. In this work, the effect of impurities and ultrasound on crystallisation processes (nucleation temperature, yield) and crystal properties (crystal size distribution determined by Focused
[...] Read more.
Sono-crystallisation has been used to enhance crystalline product quality particularly in terms of purity, particle size and size distribution. In this work, the effect of impurities and ultrasound on crystallisation processes (nucleation temperature, yield) and crystal properties (crystal size distribution determined by Focused Beam Reflectance Measurement (FBRM), crystal habit, filtration rate and impurity content in the crystal product by Liquid Chromatography-Mass Spectroscopy (LC-MS)) were investigated in bulk suspension crystallisation experiments with and without the use of ultrasound. The results demonstrate that ultrasonic intervention has a significant effect on both crystallisation and product crystal properties. It increases the nucleation rate resulting in smaller particles and a narrower Particle Size Distribution (PSD), the yield has been shown to be increase as has the product purity. The effect of ultrasound is to reduce the level acetanilide impurity incorporated during growth from a 2 mol% solution of the selected impurity from 0.85 mol% to 0.35 mol% and likewise ultrasound reduces the uptake of metacetamol from 1.88 mol% to 1.52 mol%. Full article
(This article belongs to the Special Issue Advances in Ultrasound Stimulated Crystallization)
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Open AccessArticle Formation of Cellular Structure on Metastable Solidification of Undercooled Eutectic CoSi-62 at. %
Crystals 2017, 7(10), 295; doi:10.3390/cryst7100295
Received: 13 August 2017 / Revised: 19 September 2017 / Accepted: 27 September 2017 / Published: 30 September 2017
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Abstract
The relationship between emissivity, delay time, and surface growth for metastable solidification of CoSi-62 at. % eutectic alloys is reported from undercooling experiments conducted using electrostatic levitation. A fraction of the undercooled melt is first solidified to CoSi2 with subsequent nucleation in
[...] Read more.
The relationship between emissivity, delay time, and surface growth for metastable solidification of CoSi-62 at. % eutectic alloys is reported from undercooling experiments conducted using electrostatic levitation. A fraction of the undercooled melt is first solidified to CoSi2 with subsequent nucleation in the mushy-zone of CoSi after an observed delay time. During this double recalescence event, the temperature of the secondary recalescence exceeds the liquidus, indicating that the spectral emissivity has changed. This emissivity change increases with longer delay times during solidification and is linked to the growth of cellular structure on the sample surface. Density measurements showed that the cellular structure begins to grow rapidly at a certain time during metastable solidification. This phenomenon is likely associated with the constitutional undercooling of the remaining melt. Full article
(This article belongs to the Special Issue Crystal Formation from Metastable Liquids)
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Open AccessCommunication Over-Production, Crystallization, and Preliminary X-ray Crystallographic Analysis of a Coiled-Coil Region in Human Pericentrin
Crystals 2017, 7(10), 296; doi:10.3390/cryst7100296
Received: 12 September 2017 / Revised: 27 September 2017 / Accepted: 28 September 2017 / Published: 2 October 2017
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Abstract
The genes encoding three coiled-coil regions in human pericentrin were gene synthesized with Escherichia coli codon-optimization, and the proteins were successfully over-produced in large quantities using E. coli expression. After verifying that the purified proteins were mostly composed of α-helices, one of the
[...] Read more.
The genes encoding three coiled-coil regions in human pericentrin were gene synthesized with Escherichia coli codon-optimization, and the proteins were successfully over-produced in large quantities using E. coli expression. After verifying that the purified proteins were mostly composed of α-helices, one of the proteins was crystallized using polyethylene glycol 8000 as crystallizing agent. X-ray diffraction data were collected to 3.8 Å resolution under cryo-condition using synchrotron X-ray. The crystal belonged to space group C2 with unit cell parameters a = 324.9 Å, b = 35.7 Å, c = 79.5 Å, and β = 101.6˚. According to Matthews’ coefficient, the asymmetric unit may contain up to 12 subunits of the monomeric protein, with a crystal volume per protein mass (VM) of 1.96 Å3 Da−1 and a 37.3% solvent content. Full article
(This article belongs to the Special Issue Biological and Biogenic Crystallization)
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Open AccessArticle Synthesis, Crystal Structure and Water Vapor Adsorption Properties of a Porous Supramolecular Architecture
Crystals 2017, 7(10), 297; doi:10.3390/cryst7100297
Received: 23 July 2017 / Revised: 24 September 2017 / Accepted: 29 September 2017 / Published: 2 October 2017
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Abstract
A new complex, [Cu4(HL)4(H2O)14] (1, H3L·HCl = 5-((4-carboxypiperidin-1-yl)methyl)isophthalic acid hydrochloride), has been prepared and characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy and powder X-ray diffraction (PXRD). The result of
[...] Read more.
A new complex, [Cu4(HL)4(H2O)14] (1, H3L·HCl = 5-((4-carboxypiperidin-1-yl)methyl)isophthalic acid hydrochloride), has been prepared and characterized by single-crystal X-ray diffraction, elemental analysis, IR spectroscopy and powder X-ray diffraction (PXRD). The result of the X-ray diffraction analysis reveals that the complex crystallizes in monoclinic, space group C2/c and three unique Cu(II) atoms that are connected by partially deprotonated HL2− anion to form a cyclic structure. The rich hydrogen bonding and π-π non-covalent packing interactions extend cyclic units into a three-dimensional (3D) supramolecular polymer. Moreover, the thermogravimetric (TG) analysis and water vapor adsorption property of 1 were also discussed. Full article
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Open AccessArticle Impact of Annealing Temperature on the Physical Properties of the Lanthanum Deficiency Manganites
Crystals 2017, 7(10), 301; doi:10.3390/cryst7100301
Received: 20 August 2017 / Revised: 22 September 2017 / Accepted: 2 October 2017 / Published: 5 October 2017
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Abstract
The lanthanum deficiency manganites La0.8-x□xCa0.2MnO3 (x = 0, 0.1 and 0.2), where □ is a lanthanum vacancy, were prepared using the classic ceramic methods with different thermal treatments (1373 K and 973 K).
[...] Read more.
The lanthanum deficiency manganites La0.8-x□xCa0.2MnO3 (x = 0, 0.1 and 0.2), where □ is a lanthanum vacancy, were prepared using the classic ceramic methods with different thermal treatments (1373 K and 973 K). The structural, magnetic, and magnetocaloric properties of these compounds were studied as a function of annealing temperature. It was noted that the annealing temperature did not affect the crystal structure of our samples (orthorhombic structure with Pnma space group). Nevertheless, a change in the variation of the unit cell volume V, the average bond length dMn–O, and the average bond angles θMn–O–Mn were observed. Magnetization versus temperature study has shown that all samples exhibited a magnetic transition from ferromagnetic (FM) to paramagnetic (PM) phase with increasing temperature. However, it can be clearly seen that the annealing at 973 K induced an increase of the magnetization. In addition, the magnetocaloric effect (MCE) as well as the relative cooling power (RCP) were estimated. As an important result, the values of MCE and RCP in our Lanthanum-deficiency manganites are reported to be near to those found in gadolinium, considered as magnetocaloric reference material. Full article
(This article belongs to the Special Issue Crystal Structure of Magnetic Materials)
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Open AccessFeature PaperArticle Modulating Nucleation by Kosmotropes and Chaotropes: Testing the Waters
Crystals 2017, 7(10), 0302; doi:10.3390/cryst7100302
Received: 24 August 2017 / Accepted: 4 October 2017 / Published: 6 October 2017
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Abstract
Water is a fundamental solvent sustaining life, key to the conformations and equilibria associated with solute species. Emerging studies on nucleation and crystallization phenomena reveal that the dynamics of hydration associated with mineral precursors are critical in determining material formation and growth. With
[...] Read more.
Water is a fundamental solvent sustaining life, key to the conformations and equilibria associated with solute species. Emerging studies on nucleation and crystallization phenomena reveal that the dynamics of hydration associated with mineral precursors are critical in determining material formation and growth. With certain small molecules affecting the hydration and conformational stability of co-solutes, this study systematically explores the effects of these chaotropes and kosmotropes as well as certain sugar enantiomers on the early stages of calcium carbonate formation. These small molecules appear to modulate mineral nucleation in a class-dependent manner. The observed effects are finite in comparison to the established, strong interactions between charged polymers and intermediate mineral forms. Thus, perturbations to hydration dynamics of ion clusters by co-solute species can affect nucleation phenomena in a discernable manner. Full article
(This article belongs to the Special Issue Biological and Biogenic Crystallization)
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Open AccessArticle Synthesis and Crystal Structure of a New Hydrated Benzimidazolium Salt Containing Spiro Structure
Crystals 2017, 7(10), 303; doi:10.3390/cryst7100303
Received: 23 August 2017 / Revised: 29 September 2017 / Accepted: 29 September 2017 / Published: 9 October 2017
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Abstract
A new hydrated benzimidazolium salt containing spiro structure was obtained when benzimidazole is added to ethyl alcohol of 1,5-dioxaspiro[5.5]undecane-2,4-dione and trimethoxymethane. The title compound (C19H21O8) (C7H7N2) (0.5H2O) was characterized
[...] Read more.
A new hydrated benzimidazolium salt containing spiro structure was obtained when benzimidazole is added to ethyl alcohol of 1,5-dioxaspiro[5.5]undecane-2,4-dione and trimethoxymethane. The title compound (C19H21O8) (C7H7N2) (0.5H2O) was characterized by elemental analysis, IR, UV-Vis, and single-crystal X-ray diffraction. The result shows that it belongs to the triclinic system, space group P-1, with a = 11.017(2) Å, b = 11.424(2) Å, c = 11.650(2) Å, α = 70.60(3)°, β = 71.00(3)°, γ = 67.64(3)°, Mr = 505.51, V = 1245.2(5) Å, Z = 2, Dc = 1.348 g/cm3, F(000) = 534, μ(MoKa) = 0.102 mm−1. There exist two types of hydrogen bonds in the crystal. (C19H21O8) anions and (C7H7N2)+ cations are linked by N–H···O hydrogen bonds, while (C19H21O8) anions and free water are linked by O–H···O hydrogen bonds. All of the above hydrogen bonds form a one-dimensional (1D)-chained structure. The 1D chains further links the molecule into a three-dimensional (3D)-layered structure. Full article
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Open AccessArticle Methods for Calculating Empires in Quasicrystals
Crystals 2017, 7(10), 304; doi:10.3390/cryst7100304
Received: 31 August 2017 / Revised: 26 September 2017 / Accepted: 29 September 2017 / Published: 9 October 2017
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Abstract
This paper reviews the empire problem for quasiperiodic tilings and the existing methods for generating the empires of the vertex configurations in quasicrystals, while introducing a new and more efficient method based on the cut-and-project technique. Using Penrose tiling as an example, this
[...] Read more.
This paper reviews the empire problem for quasiperiodic tilings and the existing methods for generating the empires of the vertex configurations in quasicrystals, while introducing a new and more efficient method based on the cut-and-project technique. Using Penrose tiling as an example, this method finds the forced tiles with the restrictions in the high dimensional lattice (the mother lattice) that can be cut-and-projected into the lower dimensional quasicrystal. We compare our method to the two existing methods, namely one method that uses the algorithm of the Fibonacci chain to force the Ammann bars in order to find the forced tiles of an empire and the method that follows the work of N.G. de Bruijn on constructing a Penrose tiling as the dual to a pentagrid. This new method is not only conceptually simple and clear, but it also allows us to calculate the empires of the vertex configurations in a defected quasicrystal by reversing the configuration of the quasicrystal to its higher dimensional lattice, where we then apply the restrictions. These advantages may provide a key guiding principle for phason dynamics and an important tool for self error-correction in quasicrystal growth. Full article
(This article belongs to the Special Issue Structure and Properties of Quasicrystalline Materials)
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Open AccessCommunication Synthesis, Crystal Structure and Catalytic Activity of a Novel Ba(II) Complex with Pyridine-2-Carboxaldehyde-2-Phenylacetic Acid Hydrazone Ligand
Crystals 2017, 7(10), 305; doi:10.3390/cryst7100305
Received: 13 September 2017 / Revised: 30 September 2017 / Accepted: 5 October 2017 / Published: 9 October 2017
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Abstract
A novel Ba(II) complex, [BaL2Cl2] (1) (L = pyridine-2-carboxaldehyde-2-phenylacetic acid hydrazone), has been synthesized using BaCl2, pyridine-2-carboxaldehyde and 2-phenylacetohydrazide as raw materials. The structure of 1 has been determined by elemental analysis and X-ray single-crystal diffraction technique.
[...] Read more.
A novel Ba(II) complex, [BaL2Cl2] (1) (L = pyridine-2-carboxaldehyde-2-phenylacetic acid hydrazone), has been synthesized using BaCl2, pyridine-2-carboxaldehyde and 2-phenylacetohydrazide as raw materials. The structure of 1 has been determined by elemental analysis and X-ray single-crystal diffraction technique. X-ray structural analysis showed that the Ba(II) complex (1) crystallizes in monoclinic, space group P21/c with cell parameters: a = 12.464(3) Å, b = 13.531(3) Å, c = 8.8035(18) Å, β = 95.06(3)°. In 1, the Ba(II) atom is eight-coordinated in a distorted doubly-capped octahedral geometry through four N atoms and two O atoms from two different pyridine-2-carboxaldehyde-2-phenylacetic acid hydrazone ligands and two Cl. The complex (1) forms a 3D network structure by the interaction of intermolecular N-H···Cl hydrogen bonds and π···π stacking of neighboring pyridine rings and benzene rings. The optimum conditions for the benzyl alcohol oxidation reaction using the Ba(II) complex as catalyst was investigated. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle Pinning Effect of Cerium Inclusions during Austenite Grains Growth in SS400 Steel at 1300 °C: A Combined Phase Field and Experimental Study
Crystals 2017, 7(10), 308; doi:10.3390/cryst7100308
Received: 12 September 2017 / Revised: 10 October 2017 / Accepted: 11 October 2017 / Published: 15 October 2017
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Abstract
The pinning effect of cerium inclusions in the austenite grain growth of SS400 steel at 1300 °C is investigated by using a semi-empirical-simulation. Firstly, steel samples containing cerium inclusions are prepared; then the properties of inclusions are determined using SEM. In situ observation
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The pinning effect of cerium inclusions in the austenite grain growth of SS400 steel at 1300 °C is investigated by using a semi-empirical-simulation. Firstly, steel samples containing cerium inclusions are prepared; then the properties of inclusions are determined using SEM. In situ observation of austenite grain growth is performed by LSCM, to determine the fitting parameters of the model such as the grain mobility and the pinning parameter. These parameters are directly inserted into our phase field simulation. The time-dependent Ginzburg-Landau (TDGL) equation is implemented in our phase field model, where the effects of inclusion and grain boundary interaction are inserted as a potential term in the local free energy. The results proved that the optimal size of austenite grains can be achieved by changing the volume fraction of inclusions. In fact, by increasing the volume fraction of inclusions from 0 to 0.1, the austenite grain growth can be decreased where the boundary mobility reduces from 2.3×10−12 m4/Js to 1.0×10−12 m4/Js. The results also demonstrated that increasing the temperature can provide more energy for grain to overcome the inclusions’ pinning force. Moreover, it was shown that the classical Zener model, R c = 0.45 r p f i 1 , describes the pinning effect of cerium inclusions. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Breathing 3D Frameworks with T-Shaped Connecting Ligand Exhibiting Solvent Induction, Metal Ions Effect and Luminescent Properties
Crystals 2017, 7(10), 311; doi:10.3390/cryst7100311
Received: 18 August 2017 / Revised: 6 October 2017 / Accepted: 13 October 2017 / Published: 17 October 2017
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Abstract
To study the structural effects in three-dimensional porous coordination polymers, three novel flexible porous coordination polymers—[Cd2(bpdc)2](DMF)3(H2O) (1) and [M(bpdc)](DMF)(H2O) (M = Cd (2), Zn (3))—have been synthesized
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To study the structural effects in three-dimensional porous coordination polymers, three novel flexible porous coordination polymers—[Cd2(bpdc)2](DMF)3(H2O) (1) and [M(bpdc)](DMF)(H2O) (M = Cd (2), Zn (3))—have been synthesized under solvothermal conditions with d10 block metal ions and T-shaped connecting ligand. Complexes 13 crystallize in different space groups, but they display the same ant network. The first two complexes can transform into each other via the alteration of guest, whereas complex 3 shows no structural change. The structural details reveal that the size of metal ions might be responsible for the transformation of porous frameworks. Furthermore, luminescent properties have been explored, and a guest-dependent shift of emission peaks was observed, suggesting potential application of the complexes as a probe. Full article
(This article belongs to the Special Issue Crystal Structure Analysis of Supramolecular and Porous Solids)
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Open AccessArticle Preparation of Potassium Dichromate Crystals from the Chromite Concentrate by Microwave Assisted Leaching
Crystals 2017, 7(10), 312; doi:10.3390/cryst7100312
Received: 28 August 2017 / Revised: 10 October 2017 / Accepted: 11 October 2017 / Published: 18 October 2017
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Abstract
In the present investigation, the oxidizing roasting process of chromite with sodium carbonate to prepare potassium dichromate crystals was studied in the microwave field with air, by heating the chromite and sodium carbonate. The chromite and sodium carbonate heated separately at 1000 °C
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In the present investigation, the oxidizing roasting process of chromite with sodium carbonate to prepare potassium dichromate crystals was studied in the microwave field with air, by heating the chromite and sodium carbonate. The chromite and sodium carbonate heated separately at 1000 °C in the microwave oven (frequency: 2.45 GHz; power 1.5 kW) in order to study the microwave absorption properties. The dielectric constant and dielectric loss factor of the chromite and sodium carbonate examined. Then, chromite with sodium carbonate taken in (1:2) ratio and heated at 750 °C. Thus obtained samples were characterized using various techniques includes Powder-XRD (XRD), Scanning Electron Microscopy (SEM), and X-ray fluorescence (XRF). The XRD pattern reveals the existence of Fe3O4, Fe2O3, NaAlO2, and Na2CrO4. The iron and aluminum were leached out as Fe2O3 and Al(OH)3 respectively. The resulting sample treated with the KCl to prepare potassium dichromate crystals. Finally, potassium dichromate crystals formed. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle Optical Characterization of AlAsSb Digital Alloy and Random Alloy on GaSb
Crystals 2017, 7(10), 313; doi:10.3390/cryst7100313
Received: 9 September 2017 / Revised: 13 October 2017 / Accepted: 15 October 2017 / Published: 18 October 2017
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Abstract
III-(As, Sb) alloys are building blocks for various advanced optoelectronic devices, but the growth of their ternary or quaternary materials are commonly limited by spontaneous formation of clusters and phase separations during alloying. Recently, digital alloy growth by molecular beam epitaxy has been
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III-(As, Sb) alloys are building blocks for various advanced optoelectronic devices, but the growth of their ternary or quaternary materials are commonly limited by spontaneous formation of clusters and phase separations during alloying. Recently, digital alloy growth by molecular beam epitaxy has been widely adopted in preference to conventional random alloy growth because of the extra degree of control offered by the ordered alloying. In this article, we provide a comparative study of the optical characteristics of AlAsSb alloys grown lattice-matched to GaSb using both techniques. The sample grown by digital alloy technique showed stronger photoluminescence intensity, narrower peak linewidth, and larger carrier activation energy than the random alloy technique, indicating an improved optical quality with lower density of non-radiative recombination centers. In addition, a relatively long carrier lifetime was observed from the digital alloy sample, consistent with the results obtained from the photoluminescence study. Full article
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Open AccessArticle Generating, Separating and Polarizing Terahertz Vortex Beams via Liquid Crystals with Gradient-Rotation Directors
Crystals 2017, 7(10), 314; doi:10.3390/cryst7100314
Received: 20 September 2017 / Revised: 13 October 2017 / Accepted: 15 October 2017 / Published: 18 October 2017
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Abstract
Liquid crystal (LC) is a promising candidate for terahertz (THz) devices. Recently, LC has been introduced to generate THz vortex beams. However, the efficiency is intensely dependent on the incident wavelength, and the transformed THz vortex beam is usually mixed with the residual
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Liquid crystal (LC) is a promising candidate for terahertz (THz) devices. Recently, LC has been introduced to generate THz vortex beams. However, the efficiency is intensely dependent on the incident wavelength, and the transformed THz vortex beam is usually mixed with the residual component. Thus, a separating process is indispensable. Here, we introduce a gradient blazed phase, and propose a THz LC forked polarization grating that can simultaneously generate and separate pure THz vortices with opposite circular polarization. The specific LC gradient-rotation directors are implemented by a photoalignment technique. The generated THz vortex beams are characterized with a THz imaging system, verifying features of polarization controllability. This work may pave a practical road towards generating, separating and polarizing THz vortex beams, and may prompt applications in THz communications, sensing and imaging. Full article
(This article belongs to the Special Issue Micro and Nano Patterned Substrates for Liquid Crystal Alignment)
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Open AccessArticle Crystal Engineering for Mechanical Strength at Nano-Scale Dimensions
Crystals 2017, 7(10), 315; doi:10.3390/cryst7100315
Received: 22 September 2017 / Revised: 14 October 2017 / Accepted: 15 October 2017 / Published: 18 October 2017
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Abstract
The mechanical strengths of nano-scale individual crystal or nanopolycrystalline metals, and other dimensionally-related materials are increased by an order of magnitude or more as compared to those values measured at conventional crystal or polycrystal grain dimensions. An explanation for the result is attributed
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The mechanical strengths of nano-scale individual crystal or nanopolycrystalline metals, and other dimensionally-related materials are increased by an order of magnitude or more as compared to those values measured at conventional crystal or polycrystal grain dimensions. An explanation for the result is attributed to the constraint provided at the surface of the crystals or, more importantly, at interfacial boundaries within or between crystals. The effect is most often described in terms either of two size dependencies: an inverse dependence on crystal size because of single dislocation behavior or, within a polycrystalline material, in terms of a reciprocal square root of grain size dependence, designated as a Hall-Petch relationship for the researchers first pointing to the effect for steel and who provided an enduring dislocation pile-up interpretation for the relationship. The current report provides an updated description of such strength properties for iron and steel materials, and describes applications of the relationship to a wider range of materials, including non-ferrous metals, nano-twinned, polyphase, and composite materials. At limiting small nm grain sizes, there is a generally minor strength reversal that is accompanied by an additional order-of-magnitude elevation of an increased strength dependence on deformation rate, thus giving an important emphasis to the strain rate sensitivity property of materials at nano-scale dimensions. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle Phase Transformation and Hydrogen Storage Properties of an La7.0Mg75.5Ni17.5 Hydrogen Storage Alloy
Crystals 2017, 7(10), 316; doi:10.3390/cryst7100316
Received: 25 September 2017 / Revised: 9 October 2017 / Accepted: 16 October 2017 / Published: 18 October 2017
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Abstract
X-ray diffraction showed that an La7.0Mg75.5Ni17.5 alloy prepared via inductive melting was composed of an La2Mg17 phase, an LaMg2Ni phase, and an Mg2Ni phase. After the first hydrogen absorption/desorption process, the
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X-ray diffraction showed that an La7.0Mg75.5Ni17.5 alloy prepared via inductive melting was composed of an La2Mg17 phase, an LaMg2Ni phase, and an Mg2Ni phase. After the first hydrogen absorption/desorption process, the phases of the alloy turned into an La–H phase, an Mg phase, and an Mg2Ni phase. The enthalpy and entropy derived from the van’t Hoff equation for hydriding were −42.30 kJ·mol−1 and −69.76 J·K−1·mol−1, respectively. The hydride formed in the absorption step was less stable than MgH2 (−74.50 kJ·mol−1 and −132.3 J·K−1·mol−1) and Mg2NiH4 (−64.50 kJ·mol−1 and −123.1 J·K−1·mol−1). Differential thermal analysis showed that the initial hydrogen desorption temperature of its hydride was 531 K. Compared to Mg and Mg2Ni, La7.0Mg75.5Ni17.5 is a promising hydrogen storage material that demonstrates fast adsorption/desorption kinetics as a result of the formation of an La–H compound and the synergetic effect of multiphase. Full article
(This article belongs to the Special Issue Crystal Dislocations: Their Impact on Physical Properties of Crystals)
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Open AccessArticle Synchrotron Radiation Pair Distribution Function Analysis of Gels in Cements
Crystals 2017, 7(10), 317; doi:10.3390/cryst7100317
Received: 22 September 2017 / Revised: 12 October 2017 / Accepted: 17 October 2017 / Published: 18 October 2017
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Abstract
The analysis of atomic ordering in a nanocrystalline phase with small particle sizes, below 5 nm, is intrinsically complicated because of the lack of long-range order. Furthermore, the presence of additional crystalline phase(s) may exacerbate the problem, as is the case in cement
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The analysis of atomic ordering in a nanocrystalline phase with small particle sizes, below 5 nm, is intrinsically complicated because of the lack of long-range order. Furthermore, the presence of additional crystalline phase(s) may exacerbate the problem, as is the case in cement pastes. Here, we use the synchrotron pair distribution function (PDF) chiefly to characterize the local atomic order of the nanocrystalline phases, gels, in cement pastes. We have used a multi r-range analysis approach, where the ~4–7 nm r-range allows determining the crystalline phase contents; the ~1–2.5 nm r-range is used to characterize the atomic ordering in the nanocrystalline component; and the ~0.2–1.0 nm r-range gives insights about additional amorphous components. Specifically, we have prepared four alite pastes with variable water contents, and the analyses showed that a defective tobermorite, Ca11Si9O28(OH)2.8.5H2O, gave the best fit. Furthermore, the PDF analyses suggest that the calcium silicate hydrate gel is composed of this tobermorite and amorphous calcium hydroxide. Finally, this approach has been used to study alternative cements. The hydration of monocalcium aluminate and ye’elimite pastes yield aluminum hydroxide gels. PDF analyses show that these gels are constituted of nanocrystalline gibbsite, and the particle size can be as small as 2.5 nm. Full article
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Open AccessArticle Binuclear Copper(I) Borohydride Complex Containing Bridging Bis(diphenylphosphino) Methane Ligands: Polymorphic Structures of [(µ2-dppm)2Cu22-BH4)2] Dichloromethane Solvate
Crystals 2017, 7(10), 318; doi:10.3390/cryst7100318
Received: 18 September 2017 / Revised: 13 October 2017 / Accepted: 17 October 2017 / Published: 20 October 2017
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Abstract
Bis(diphenylphosphino)methane copper(I) tetrahydroborate was synthesized by ligands exchange in bis(triphenylphosphine) copper(I) tetrahydroborate, and characterized by XRD, FTIR, NMR spectroscopy. According to XRD the title compound has dimeric structure, [(μ2-dppm)2Cu22-BH4)2], and crystallizes
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Bis(diphenylphosphino)methane copper(I) tetrahydroborate was synthesized by ligands exchange in bis(triphenylphosphine) copper(I) tetrahydroborate, and characterized by XRD, FTIR, NMR spectroscopy. According to XRD the title compound has dimeric structure, [(μ2-dppm)2Cu22-BH4)2], and crystallizes as CH2Cl2 solvate in two polymorphic forms (orthorhombic, 1, and monoclinic, 2) The details of molecular geometry and the crystal-packing pattern in polymorphs were studied. The rare Twisted Boat-Boat conformation of the core Cu2P4C2 cycle in 1 is found being more stable than Boat-Boat conformation in 2. Full article
(This article belongs to the Special Issue Crystal Structures of Boron Compounds)
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Open AccessArticle Formation Mechanism of CaCO3 Spherulites in the Myostracum Layer of Limpet Shells
Crystals 2017, 7(10), 319; doi:10.3390/cryst7100319
Received: 14 August 2017 / Revised: 16 October 2017 / Accepted: 16 October 2017 / Published: 23 October 2017
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Abstract
CaCO3 spherulites were found in the myostracum layer of common limpet shells collected from East Sands, St Andrews, Scotland. Their microstructures were revealed by using powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray microanalysis. The formation
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CaCO3 spherulites were found in the myostracum layer of common limpet shells collected from East Sands, St Andrews, Scotland. Their microstructures were revealed by using powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray microanalysis. The formation mechanisms of these spherulites and their morphology evolution were postulated. It was proposed that spherical particles of an inorganic and biological composite formed first. In the centre of each spherical particle a double-layer disk of vaterite crystal sandwiching a biological sheet developed. The disk crystal supplies a relatively strong mirror symmetric dipole field, guiding the orientations of the nanocrystallites and the arrangement of mesorods and, therefore, determining the final morphology of the spherulite. Full article
(This article belongs to the Special Issue Biological and Biogenic Crystallization)
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Open AccessArticle FOX, Current State and Possibilities
Crystals 2017, 7(10), 322; doi:10.3390/cryst7100322
Received: 15 August 2017 / Revised: 25 September 2017 / Accepted: 13 October 2017 / Published: 24 October 2017
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Abstract
FOX (Free Objects for Xtallography) is a computer program for solving crystal structures of all types of compounds using the powder data (but also the single crystal data) measured using X-ray, neutron and electron diffraction. It works in direct space using the reversed
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FOX (Free Objects for Xtallography) is a computer program for solving crystal structures of all types of compounds using the powder data (but also the single crystal data) measured using X-ray, neutron and electron diffraction. It works in direct space using the reversed Monte Carlo algorithm of global optimization. Since its release fifteen years ago, it has developed into a powerful tool, simplifying the powder pattern analysis starting from the background determination, indexing and space group selection over the structure modelling using various pre-programmed structural fragments up to the validation of the proposed structural model. Full article
(This article belongs to the Special Issue Structural Analysis of Crystalline Materials from Powders)
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Review

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Open AccessReview Progress in Indentation Study of Materials via Both Experimental and Numerical Methods
Crystals 2017, 7(10), 258; doi:10.3390/cryst7100258
Received: 19 June 2017 / Revised: 8 August 2017 / Accepted: 9 August 2017 / Published: 13 October 2017
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Abstract
Indentation as a method to characterize materials has a history of more than 117 years. However, to date, it is still the most popular way to measure the mechanical properties of various materials at microscale and nanoscale. This review summarizes the background and
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Indentation as a method to characterize materials has a history of more than 117 years. However, to date, it is still the most popular way to measure the mechanical properties of various materials at microscale and nanoscale. This review summarizes the background and the basic principle of processing by indentation. It is demonstrated that indentation is an effective and efficient method to identify mechanical properties, such as hardness, Young’s modulus, etc., of materials at smaller scale, when the traditional tensile tests could not be applied. The review also describes indentation process via both experimental tests and numerical modelling in recent studies. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessReview Back to the Structural and Dynamical Properties of Neutral-Ionic Phase Transitions
Crystals 2017, 7(10), 285; doi:10.3390/cryst7100285
Received: 1 August 2017 / Revised: 12 September 2017 / Accepted: 13 September 2017 / Published: 23 September 2017
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Abstract
Although the Neutral-Ionic transition in mixed stack charge-transfer crystals was discovered almost forty years ago, many features of this intriguing phase transition, as well as open questions, remain at the heart of today’s science. First of all, there is the most spectacular manifestation
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Although the Neutral-Ionic transition in mixed stack charge-transfer crystals was discovered almost forty years ago, many features of this intriguing phase transition, as well as open questions, remain at the heart of today’s science. First of all, there is the most spectacular manifestation of electronic ferroelectricity, in connection with a high degree of covalency between alternating donor and acceptor molecules along stacks. In addition, a charge-transfer instability from a quasi-neutral to a quasi-ionic state takes place concomitantly with the stack dimerization, which breaks the inversion symmetry. Moreover, these systems exhibit exceptional one-dimensional fluctuations, with an enhancement of the effects of electron-lattice interaction. This may lead to original physical pictures for the dynamics of pre-transitional phenomena, as the possibility of a pronounced Peierls-type instability and/or the generation of unconventional non-linear excitations along stacks. Last but not least, these mixed stack charge-transfer systems constitute a valuable test bed to explore some of the key questions of ultrafast photo-induced phenomena, such as multiscale dynamics, selective coherent excitations and non-linear responsiveness. These different aspects will be discussed through the structural and dynamical features of the neutral-ionic transition, considering old and recent results, open questions and future opportunities. In particular, we revisit the structural changes and symmetry considerations, the pressure-temperature phase diagrams and conclude by their interplay with the photo-induced dynamics. Full article
(This article belongs to the Special Issue The Neutral–Ionic Phase Transition)
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Open AccessReview The Orbital Angular Momentum Modes Supporting Fibers Based on the Photonic Crystal Fiber Structure
Crystals 2017, 7(10), 286; doi:10.3390/cryst7100286
Received: 24 July 2017 / Revised: 20 September 2017 / Accepted: 20 September 2017 / Published: 6 October 2017
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Abstract
The orbital angular momentum (OAM) of light can be another physical dimension that we exploit to make multiplexing in the spatial domain. The design of the OAM mode supporting fiber attracts many attentions in the field of the space division multiplexing (SDM) system.
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The orbital angular momentum (OAM) of light can be another physical dimension that we exploit to make multiplexing in the spatial domain. The design of the OAM mode supporting fiber attracts many attentions in the field of the space division multiplexing (SDM) system. This paper reviews the recent progresses in photonic crystal fiber (PCF) supporting OAM modes, and summarizes why a PCF structure can be used to support stable OAM transmission modes. The emphasis is on the circular PCFs, which possess many excellent features of transmission performance, such as good-quality OAM modes, enough separation of the effective indices, low confinement loss, flat dispersion, a large effective area, and a low nonlinear coefficient. We also compare the transmission properties between the circular PCF and the ring core fiber, as well as the properties between the OAM EDFA based on circular PCF and the OAM EDFA based on the ring core fiber. At last, the challenges and prospects of OAM fibers based on the PCF structure are also discussed. Full article
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Open AccessReview Anti-Solvent Crystallization Strategies for Highly Efficient Perovskite Solar Cells
Crystals 2017, 7(10), 291; doi:10.3390/cryst7100291
Received: 3 September 2017 / Revised: 25 September 2017 / Accepted: 26 September 2017 / Published: 28 September 2017
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Abstract
Solution-processed organic-inorganic halide perovskites are currently established as the hottest area of interest in the world of photovoltaics, ensuring low manufacturing cost and high conversion efficiencies. Even though various fabrication/deposition approaches and device architectures have been tested, researchers quickly realized that the key
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Solution-processed organic-inorganic halide perovskites are currently established as the hottest area of interest in the world of photovoltaics, ensuring low manufacturing cost and high conversion efficiencies. Even though various fabrication/deposition approaches and device architectures have been tested, researchers quickly realized that the key for the excellent solar cell operation was the quality of the crystallization of the perovskite film, employed to assure efficient photogeneration of carriers, charge separation and transport of the separated carriers at the contacts. One of the most typical methods in chemistry to crystallize a material is anti-solvent precipitation. Indeed, this classical precipitation method worked really well for the growth of single crystals of perovskite. Fortunately, the method was also effective for the preparation of perovskite films by adopting an anti-solvent dripping technique during spin-coating the perovskite precursor solution on the substrate. With this, polycrystalline perovskite films with pure and stable crystal phases accompanied with excellent surface coverage were prepared, leading to highly reproducible efficiencies close to 22%. In this review, we discuss recent results on highly efficient solar cells, obtained by the anti-solvent dripping method, always in the presence of Lewis base adducts of lead(II) iodide. We present all the anti-solvents that can be used and what is the impact of them on device efficiencies. Finally, we analyze the critical challenges that currently limit the efficacy/reproducibility of this crystallization method and propose prospects for future directions. Full article
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Open AccessReview Recent Advances in Two-Dimensional Materials with Charge Density Waves: Synthesis, Characterization and Applications
Crystals 2017, 7(10), 298; doi:10.3390/cryst7100298
Received: 10 August 2017 / Revised: 25 September 2017 / Accepted: 26 September 2017 / Published: 3 October 2017
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Abstract
Recently, two-dimensional (2D) charge density wave (CDW) materials have attracted extensive interest due to potential applications as high performance functional nanomaterials. As other 2D materials, 2D CDW materials are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into layers
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Recently, two-dimensional (2D) charge density wave (CDW) materials have attracted extensive interest due to potential applications as high performance functional nanomaterials. As other 2D materials, 2D CDW materials are layered materials with strong in-plane bonding and weak out-of-plane interactions enabling exfoliation into layers of single unit cell thickness. Although bulk CDW materials have been studied for decades, recent developments in nanoscale characterization and device fabrication have opened up new opportunities allowing applications such as oscillators, electrodes in supercapacitors, energy storage and conversion, sensors and spinelectronic devices. In this review, we first outline the synthesis techniques of 2D CDW materials including mechanical exfoliation, liquid exfoliation, chemical vapor transport (CVT), chemical vapor deposition (CVD), molecular beam epitaxy (MBE) and electrochemical exfoliation. Then, the characterization procedure of the 2D CDW materials such as temperature-dependent Raman spectroscopy, temperature-dependent resistivity, magnetic susceptibility and scanning tunneling microscopy (STM) are reviewed. Finally, applications of 2D CDW materials are reviewed. Full article
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Open AccessReview An Overview on Magnetic Field and Electric Field Interactions with Ice Crystallisation; Application in the Case of Frozen Food
Crystals 2017, 7(10), 299; doi:10.3390/cryst7100299
Received: 4 September 2017 / Revised: 27 September 2017 / Accepted: 29 September 2017 / Published: 4 October 2017
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Abstract
Ice nucleation is a stochastic process and it is very difficult to be controlled. Freezing technologies and more specifically crystallisation assisted by magnetic, electric and electromagnetic fields have the capability to interact with nucleation. Static magnetic field (SMF) may affect matter crystallisation; however,
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Ice nucleation is a stochastic process and it is very difficult to be controlled. Freezing technologies and more specifically crystallisation assisted by magnetic, electric and electromagnetic fields have the capability to interact with nucleation. Static magnetic field (SMF) may affect matter crystallisation; however, this is still under debate in the literature. Static electric field (SEF) has a significant effect on crystallisation; this has been evidenced experimentally and confirmed by the theory. Oscillating magnetic field induces an oscillating electric field and is also expected to interact with water crystallisation. Oscillating electromagnetic fields interact with water, perturb and even disrupt hydrogen bonds, which in turn are thought to increase the degree of supercooling and to generate numerous fine ice crystals. Based on the literature, it seems that the frequency has an influence on the above-mentioned phenomena. This review article summarizes the fundamentals of freezing under magnetic, electric and electromagnetic fields, as well as their applicability and potentials within the food industry. Full article
(This article belongs to the Special Issue Crystal Formation from Metastable Liquids)
Open AccessReview Status of Growth of Group III-Nitride Heterostructures for Deep Ultraviolet Light-Emitting Diodes
Crystals 2017, 7(10), 300; doi:10.3390/cryst7100300
Received: 4 September 2017 / Revised: 28 September 2017 / Accepted: 29 September 2017 / Published: 4 October 2017
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Abstract
We overview recent progress in growth aspects of group III-nitride heterostructures for deep ultraviolet (DUV) light-emitting diodes (LEDs), with particular emphasis on the growth approaches for attaining high-quality AlN and high Al-molar fraction AlGaN. The discussion commences with the introduction of the current
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We overview recent progress in growth aspects of group III-nitride heterostructures for deep ultraviolet (DUV) light-emitting diodes (LEDs), with particular emphasis on the growth approaches for attaining high-quality AlN and high Al-molar fraction AlGaN. The discussion commences with the introduction of the current status of group III-nitride DUV LEDs and the remaining challenges. This segues into discussion of LED designs enabling high device performance followed by the review of advances in the methods for the growth of bulk single crystal AlN intended as a native substrate together with a discussion of its UV transparency. It should be stated, however, that due to the high-cost of bulk AlN substrates at the time of writing, the growth of DUV LEDs on foreign substrates such as sapphire still dominates the field. On the deposition front, the heteroepitaxial growth approaches incorporate high-temperature metal organic chemical vapor deposition (MOCVD) and pulsed-flow growth, a variant of MOCVD, with the overarching goal of enhancing adatom surface mobility, and thus epitaxial lateral overgrowth which culminates in minimization the effect of lattice- and thermal-mismatches. This is followed by addressing the benefits of pseudomorphic growth of strained high Al-molar fraction AlGaN on AlN. Finally, methods utilized to enhance both p- and n-type conductivity of high Al-molar fraction AlGaN are reviewed. Full article
(This article belongs to the Special Issue Advances in GaN Crystals and Their Applications)
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Open AccessReview Heterojunctions Based on II-VI Compound Semiconductor One-Dimensional Nanostructures and Their Optoelectronic Applications
Crystals 2017, 7(10), 307; doi:10.3390/cryst7100307
Received: 1 August 2017 / Revised: 29 September 2017 / Accepted: 10 October 2017 / Published: 20 October 2017
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Abstract
Wide band gap II-VI semiconductor nanostructures have been extensively studied according to their great potentials for optoelectronic applications, while heterojunctions are fundamental elements for modern electronic and optoelectronic devices. Subsequently, a great deal of achievements in construction and optoelectronic applications of heterojunctions based
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Wide band gap II-VI semiconductor nanostructures have been extensively studied according to their great potentials for optoelectronic applications, while heterojunctions are fundamental elements for modern electronic and optoelectronic devices. Subsequently, a great deal of achievements in construction and optoelectronic applications of heterojunctions based on II-VI compound semiconductor one-dimensional nanostructures have been obtained in the past decade. Herein, we present a review of a series of progress in this field. First, construction strategies towards different types of heterojunctions are reviewed, including core-shell heterojunctions, one-dimensional axial heterojunctions, crossed nanowires heterojunctions, and one-dimensional nanostructure/thin film or Si substrate heterojunctions. Secondly, optoelectronic applications of these constructed heterojunctions, such as photodetectors, solar cells, light emitting diodes, junction field effect transistors, etc., are discussed briefly. This review shows that heterojunctions based on II-VI compound semiconductor 1-D nanostructures have great potential for future optoelectronic applications. Full article
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Open AccessReview Challenges of Handling, Processing, and Studying Liquid and Supercooled Materials at Temperatures above 3000 K with Electrostatic Levitation
Crystals 2017, 7(10), 309; doi:10.3390/cryst7100309
Received: 13 July 2017 / Revised: 13 September 2017 / Accepted: 12 October 2017 / Published: 15 October 2017
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Abstract
Over the last 20 years, great progress has been made in techniques for electrostatic levitation, with innovations such as containerless thermophysical property measurements and combination of levitators with synchrotron radiation source and neutron beams, to name but a few. This review focuses on
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Over the last 20 years, great progress has been made in techniques for electrostatic levitation, with innovations such as containerless thermophysical property measurements and combination of levitators with synchrotron radiation source and neutron beams, to name but a few. This review focuses on the technological developments necessary for handling materials whose melting temperatures are above 3000 K. Although the original electrostatic levitator designed by Rhim et al. allowed the handling, processing, and study of most metals with melting points below 2500 K, several issues appeared, in addition to the risk of contamination, when metals such as Os, Re, and W were processed. This paper describes the procedures and the innovations that made successful levitation and the study of refractory metals at extreme temperatures (>3000 K) possible; namely, sample handling, electrode design (shape and material), levitation initiation, laser heating configuration, and UV range imaging. Typical results are also presented, putting emphasis on the measurements of density, surface tension, and viscosity of refractory materials in their liquid and supercooled phases. The data obtained are exemplified by tungsten, which has the highest melting temperature among metals (and is second only to carbon in the periodic table), rhenium and osmium. The remaining technical difficulties such as temperature measurement and evaporation are discussed. Full article
(This article belongs to the Special Issue Crystal Formation from Metastable Liquids)
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Open AccessReview Recent Insights into the Crystallization Process; Protein Crystal Nucleation and Growth Peculiarities; Processes in the Presence of Electric Fields
Crystals 2017, 7(10), 310; doi:10.3390/cryst7100310
Received: 22 September 2017 / Revised: 11 October 2017 / Accepted: 12 October 2017 / Published: 15 October 2017
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Abstract
Three-dimensional protein molecule structures are essential for acquiring a deeper insight of the human genome, and for developing novel protein-based pharmaceuticals. X-ray diffraction studies of such structures require well-diffracting protein crystals. A set of external physical factors may promote and direct protein crystallization
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Three-dimensional protein molecule structures are essential for acquiring a deeper insight of the human genome, and for developing novel protein-based pharmaceuticals. X-ray diffraction studies of such structures require well-diffracting protein crystals. A set of external physical factors may promote and direct protein crystallization so that crystals obtained are useful for X-ray studies. Application of electric fields aids control over protein crystal size and diffraction quality. Protein crystal nucleation and growth in the presence of electric fields are reviewed. A notion of mesoscopic level of impact on the protein crystallization exercised by an electric field is also considered. Full article
(This article belongs to the Special Issue Protein Crystallization under the Presence of an Electric Field)
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Open AccessReview Review of Nanoindentation Size Effect: Experiments and Atomistic Simulation
Crystals 2017, 7(10), 321; doi:10.3390/cryst7100321
Received: 26 September 2017 / Revised: 17 October 2017 / Accepted: 20 October 2017 / Published: 23 October 2017
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Abstract
Nanoindentation is a well-stablished experiment to study the mechanical properties of materials at the small length scales of micro and nano. Unlike the conventional indentation experiments, the nanoindentation response of the material depends on the corresponding length scales, such as indentation depth, which
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Nanoindentation is a well-stablished experiment to study the mechanical properties of materials at the small length scales of micro and nano. Unlike the conventional indentation experiments, the nanoindentation response of the material depends on the corresponding length scales, such as indentation depth, which is commonly termed the size effect. In the current work, first, the conventional experimental observations and theoretical models of the size effect during nanoindentation are reviewed in the case of crystalline metals, which are the focus of the current work. Next, the recent advancements in the visualization of the dislocation structure during the nanoindentation experiment is discussed, and the observed underlying mechanisms of the size effect are addressed. Finally, the recent computer simulations using molecular dynamics are reviewed as a powerful tool to investigate the nanoindentation experiment and its governing mechanisms of the size effect. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessTechnical Note Time-Varying Characteristics of Granite Microstructures after Cyclic Dynamic Disturbance Using Nuclear Magnetic Resonance
Crystals 2017, 7(10), 306; doi:10.3390/cryst7100306
Received: 2 August 2017 / Revised: 6 October 2017 / Accepted: 10 October 2017 / Published: 12 October 2017
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Abstract
To investigate the variation in the characteristics of rock microstructure after cyclic dynamic disturbances, a split Hopkinson pressure bar (SHPB) was used to carry out cyclic dynamic impact tests on granite, and the P-wave velocity was used as the characteristic parameter representing the
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To investigate the variation in the characteristics of rock microstructure after cyclic dynamic disturbances, a split Hopkinson pressure bar (SHPB) was used to carry out cyclic dynamic impact tests on granite, and the P-wave velocity was used as the characteristic parameter representing the microstructural change. Using the nuclear magnetic resonance (NMR) technique, the porosity and the T2 distribution of rock samples were obtained. The results show that, after the cyclic dynamic disturbance, the P-wave velocity within the rock specimen decreases but rebounds with time. At the elastic phase, when the axial loading increases, the P-wave velocity declines. The T2 limit is shortened, and the cyclic dynamic disturbance process promotes the formation of small pores and decreases the size and quantity of large pores. After the cyclic dynamic disturbance, the porosity of the rock samples was reduced. Full article
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