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Crystals, Volume 7, Issue 11 (November 2017)

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Open AccessArticle First-Principles Study of the Nonlinear Elasticity of Rare-Earth Hexaborides REB6 (RE = La, Ce)
Crystals 2017, 7(11), 320; doi:10.3390/cryst7110320
Received: 30 March 2017 / Revised: 16 October 2017 / Accepted: 20 October 2017 / Published: 25 October 2017
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Abstract
The complete set of independent second- and third-order elastic constants of rare-earth hexaborides LaB6 and CeB6 are determined by the combination method of first-principles calculations and homogeneous deformation theory. The ground-state lattice parameters, second-order elastic constants, and bulk modulus are in
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The complete set of independent second- and third-order elastic constants of rare-earth hexaborides LaB 6 and CeB 6 are determined by the combination method of first-principles calculations and homogeneous deformation theory. The ground-state lattice parameters, second-order elastic constants, and bulk modulus are in reasonable agreement with the available experimental data. The third-order elastic constant of longitudinal mode C 111 has a larger absolute value than other shear modes, showing the contribution to lattice vibrations from longitudinal modes to be greater. The pressure derivatives of the second-order elastic constants related to the third-order elastic constants are calculated to be positive for the two hexaborides, which are consistent with those of their polycrystalline bulk modulus and shear modulus. Furthermore, the effect of pressure on the structural stability, mechanical property, and elastic anisotropy of the two hexaborides are investigated, showing a reduction in mechanical stability and an increase in ductility and anisotropy with increasing pressure. Full article
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Open AccessArticle Longitudinal Near-Field Coupling between Acoustic Resonators Grafted onto a Waveguide
Crystals 2017, 7(11), 323; doi:10.3390/cryst7110323
Received: 3 October 2017 / Revised: 20 October 2017 / Accepted: 23 October 2017 / Published: 26 October 2017
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Abstract
We investigate longitudinal near-field coupling between acoustic resonators grafted along a waveguide. Experiments are performed in the audible range with a simple acoustic system composed of a finite aperiodic sequence of air resonators. Transmission typically shows a zero around a resonance frequency of
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We investigate longitudinal near-field coupling between acoustic resonators grafted along a waveguide. Experiments are performed in the audible range with a simple acoustic system composed of a finite aperiodic sequence of air resonators. Transmission typically shows a zero around a resonance frequency of a single resonator, as is well known. When two identical resonators are brought in close proximity, however, we observe that longitudinal near-field coupling strongly influences the acoustic transmission. When the separation between resonators is increased so that they can be considered in the far field of one another, we further observe the appearance of Fano-like transmission profiles. We explain this observation by the formation of locally resonant Fabry-Perot interferometers from every pair of resonators. All experimental results are compared to three-dimensional finite element analysis of the acoustic system. Full article
(This article belongs to the Special Issue Phononics)
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Open AccessArticle High-Throughput Small-Molecule Crystallography at the ‘Belok’ Beamline of the Kurchatov Synchrotron Radiation Source: Transition Metal Complexes with Azomethine Ligands as a Case Study
Crystals 2017, 7(11), 325; doi:10.3390/cryst7110325
Received: 10 October 2017 / Revised: 19 October 2017 / Accepted: 24 October 2017 / Published: 28 October 2017
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Abstract
This paper concisely describes capabilities of the ‘Belok’ beamline at the Kurchatov synchrotron radiation source, related to high-throughput small-molecule X-ray crystallography. As case examples, a series of four novel transition metal complexes with azomethine ligands were selected. The complexes demonstrate somewhat unexpected changes
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This paper concisely describes capabilities of the ‘Belok’ beamline at the Kurchatov synchrotron radiation source, related to high-throughput small-molecule X-ray crystallography. As case examples, a series of four novel transition metal complexes with azomethine ligands were selected. The complexes demonstrate somewhat unexpected changes in the coordination geometry and nuclearity in response to the introduction of substituents in the ligand’s periphery. Full article
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Open AccessCommunication Tetrel, Chalcogen, and Charge-Assisted Hydrogen Bonds in 2-((2-Carboxy-1-(substituted)-2-hydroxyethyl)thio) Pyridin-1-ium Chlorides
Crystals 2017, 7(11), 327; doi:10.3390/cryst7110327
Received: 9 October 2017 / Revised: 24 October 2017 / Accepted: 26 October 2017 / Published: 28 October 2017
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Abstract
Reaction of 2-chloro-2-(diethoxymethyl)-3-substitutedoxirane or 1-chloro-1-(substituted) -3,3-diethoxypropan-2-one with pyridine-2-thiol in EtOH at 25 °C yields 3-(diethoxymethyl)-3-hydroxy-2-substituted-2,3-dihydrothiazolo[3,2-a]pyridin-4-ium chlorides, which subsequently, in MeCN at 85°C, transforms into ring-opening products, 2-((2-carboxy-1-(substituted) -2-hydroxyethyl)thio)pyridin-1-ium chlorides. The tetrel (C···O) and chalcogen (S···O) bonds are found in the structures of 5
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Reaction of 2-chloro-2-(diethoxymethyl)-3-substitutedoxirane or 1-chloro-1-(substituted) -3,3-diethoxypropan-2-one with pyridine-2-thiol in EtOH at 25 °C yields 3-(diethoxymethyl)-3-hydroxy-2-substituted-2,3-dihydrothiazolo[3,2-a]pyridin-4-ium chlorides, which subsequently, in MeCN at 85°C, transforms into ring-opening products, 2-((2-carboxy-1-(substituted) -2-hydroxyethyl)thio)pyridin-1-ium chlorides. The tetrel (C···O) and chalcogen (S···O) bonds are found in the structures of 5 and 6, respectively. Compound 6 is also present in halogen bonding with a short O···Cl distance (3.067 Å). Both molecules are stabilized in crystal by tetrel, chalcogen, and multiple charge-assisted hydrogen bonds. Full article
(This article belongs to the Special Issue Chalcogen Bonding in Crystalline and Catalyst Materials)
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Open AccessArticle Band Structures Analysis Method of Two-Dimensional Phononic Crystals Using Wavelet-Based Elements
Crystals 2017, 7(11), 328; doi:10.3390/cryst7110328
Received: 12 September 2017 / Revised: 17 October 2017 / Accepted: 27 October 2017 / Published: 31 October 2017
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Abstract
A wavelet-based finite element method (WFEM) is developed to calculate the elastic band structures of two-dimensional phononic crystals (2DPCs), which are composed of square lattices of solid cuboids in a solid matrix. In a unit cell, a new model of band-gap calculation of
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A wavelet-based finite element method (WFEM) is developed to calculate the elastic band structures of two-dimensional phononic crystals (2DPCs), which are composed of square lattices of solid cuboids in a solid matrix. In a unit cell, a new model of band-gap calculation of 2DPCs is constructed using plane elastomechanical elements based on a B-spline wavelet on the interval (BSWI). Substituting the periodic boundary conditions (BCs) and interface conditions, a linear eigenvalue problem dependent on the Bloch wave vector is derived. Numerical examples show that the proposed method performs well for band structure problems when compared with those calculated by traditional FEM. This study also illustrates that filling fractions, material parameters, and incline angles of a 2DPC structure can cause band-gap width and location changes. Full article
(This article belongs to the Special Issue Phononics)
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Open AccessArticle High-Pressure Reactivity of Kr and F2—Stabilization of Krypton in the +4 Oxidation State
Crystals 2017, 7(11), 329; doi:10.3390/cryst7110329
Received: 29 September 2017 / Revised: 24 October 2017 / Accepted: 25 October 2017 / Published: 28 October 2017
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Abstract
Since the synthesis of the first krypton compound, several other Kr-bearing connections have been obtained. However, in all of them krypton adopts the +2 oxidation state, in contrast to xenon which forms numerous compounds with an oxidation state as high as +8. Motivated
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Since the synthesis of the first krypton compound, several other Kr-bearing connections have been obtained. However, in all of them krypton adopts the +2 oxidation state, in contrast to xenon which forms numerous compounds with an oxidation state as high as +8. Motivated by the possibility of thermodynamic stabilization of exotic compounds with the use of high pressure (exceeding 1 GPa = 10 kbar), we present here theoretical investigations into the chemistry of krypton and fluorine at such large compression. In particular we focus on krypton tetrafluoride, KrF4, a molecular crystal in which krypton forms short covalent bonds with neighboring fluorine atoms thus adopting the +4 oxidation state. We find that this hitherto unknown compound can be stabilized at pressures below 50 GPa. Our results indicate also that, at larger compressions, a multitude of other KrmFn fluorides should be stable, among them KrF which exhibits covalent Kr–Kr bonds. Our results set the stage for future high-pressure synthesis of novel krypton compounds. Full article
(This article belongs to the Special Issue Structure and Properties of Fluoride-based Materials)
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Open AccessCommunication Crystallisation and Preliminary Crystallographic Analysis of Helicobacter pylori Periplasmic Binding Protein YckK
Crystals 2017, 7(11), 330; doi:10.3390/cryst7110330
Received: 7 September 2017 / Revised: 26 October 2017 / Accepted: 26 October 2017 / Published: 29 October 2017
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Abstract
Helicobacter pylori infection can lead to the development of gastric and duodenal ulcers and gastric cancer. In recent years, the efficacy of the standard therapy has been falling, necessitating ongoing efforts to identify new drug targets. Due to their important role in chemotaxis
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Helicobacter pylori infection can lead to the development of gastric and duodenal ulcers and gastric cancer. In recent years, the efficacy of the standard therapy has been falling, necessitating ongoing efforts to identify new drug targets. Due to their important role in chemotaxis and nutrient uptake, periplasmic binding proteins (PBPs) represent potential targets for new antimicrobial agents that have not yet been fully explored and exploited. The H. pylori PBP YckK is homologous to polar amino acid-binding proteins from other bacteria. The yckK gene overlaps the gene tcyB—a gene annotated as a polar amino acid-transporting permease. Purified recombinant YckK behaved as a monomer in solution. Crystals of YckK were grown by the hanging drop vapour diffusion method using PEG 3350 as the precipitating agent. The crystals belong to the primitive triclinic space group P1 with unit cell parameters a = 63.0, b = 63.5, c = 74.6 Å, α = 72.5, β = 68.3, γ = 69.4°. X-ray diffraction data were collected to 1.8 Å resolution using synchrotron radiation. Molecular replacement using this data revealed that the asymmetric unit contains three subunits: two in the open and one in the closed conformation. Full article
(This article belongs to the Section Biomolecular Crystals)
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Open AccessArticle The Use of Size Exclusion Chromatography to Monitor Protein Self-Assembly
Crystals 2017, 7(11), 331; doi:10.3390/cryst7110331
Received: 6 September 2017 / Revised: 20 October 2017 / Accepted: 23 October 2017 / Published: 31 October 2017
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Abstract
High resolution size exclusion chromatography (SEC) coupled with static light scattering (SLS) analyses were conducted to study the effect of the mobile phase ionic strength and protein concentration on the output of SEC experiments. The results highlight the effect of small changes in
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High resolution size exclusion chromatography (SEC) coupled with static light scattering (SLS) analyses were conducted to study the effect of the mobile phase ionic strength and protein concentration on the output of SEC experiments. The results highlight the effect of small changes in the mobile phase composition on the estimation of molar masses estimated from retention time-based calibration curve compared with those obtained from SLS analysis. By comparing the SLS data with the SEC chromatograms, we show that SEC can provide helpful information on the protein aggregation state as macromolecules approach known precipitation points in their phase diagrams. This suggests the potential use of SEC as an easily accessible lab-based scanning methodology to monitor protein self-assembly prior to nucleation and crystallization. Implications for the use of SEC to study protein phase diagrams are discussed. Full article
(This article belongs to the Special Issue Recent Advances in Protein Crystallography)
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Open AccessArticle Halogen and Hydrogen Bonding in Multicomponent Crystals of Tetrabromo-1H-Benzotriazole
Crystals 2017, 7(11), 332; doi:10.3390/cryst7110332
Received: 18 September 2017 / Revised: 18 October 2017 / Accepted: 26 October 2017 / Published: 31 October 2017
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Abstract
4,5,6,7-Tetrabromo-1H-benzotriazole (TBBT) is still considered a reference inhibitor of casein kinase II (CK2), a valuable target for anticancer therapy, even though the poor solubility in water of this active pharmaceutical ingredient (API) has prevented its implementation in therapy. We decided to
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4,5,6,7-Tetrabromo-1H-benzotriazole (TBBT) is still considered a reference inhibitor of casein kinase II (CK2), a valuable target for anticancer therapy, even though the poor solubility in water of this active pharmaceutical ingredient (API) has prevented its implementation in therapy. We decided to explore the interactions preferentially formed by TBBT in crystalline solids in order to obtain information helpful for the development of new TBBT cocrystals possibly endowed with improved bioavailability. In this paper, we describe the synthesis and the structural characterization of the TBBT methanol solvate and of the TBBT salt with N,N,N’,N’-tetramethylethylenediamine. It is shown that TBBT can give rise to several competing interactions. This API is clearly a good halogen bond (XB) donor, with bromine atoms adjacent to the triazole ring possibly better donors than the two others. TBBT is also a good hydrogen bond (HB) donor, with the triazole hydrogen forming an HB with the acceptor or being transferred to it. Interestingly, one of the triazole nitrogens was proven to be able to work as a hydrogen bond acceptor. Full article
(This article belongs to the Special Issue Analysis of Halogen and Other σ-Hole Bonds in Crystals)
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Open AccessArticle Comparative Study of Phase Transformation in Single-Crystal Germanium during Single and Cyclic Nanoindentation
Crystals 2017, 7(11), 333; doi:10.3390/cryst7110333
Received: 30 September 2017 / Revised: 29 October 2017 / Accepted: 30 October 2017 / Published: 1 November 2017
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Abstract
Single-crystal germanium is a semiconductor material which shows complicated phase transformation under high pressure. In this study, new insight into the phase transformation of diamond-cubic germanium (dc-Ge) was attempted by controlled cyclic nanoindentation combined with Raman spectroscopic analysis. Phase transformation from dc-Ge to
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Single-crystal germanium is a semiconductor material which shows complicated phase transformation under high pressure. In this study, new insight into the phase transformation of diamond-cubic germanium (dc-Ge) was attempted by controlled cyclic nanoindentation combined with Raman spectroscopic analysis. Phase transformation from dc-Ge to rhombohedral phase (r8-Ge) was experimentally confirmed for both single and cyclic nanoindentation under high loading/unloading rates. However, compared to single indentation, double cyclic indentation with a low holding load between the cycles caused more frequent phase transformation events. Double cyclic indentation caused more stress in Ge than single indentation and increased the possibility of phase transformation. With increase in the holding load, the number of phase transformation events decreased and finally became less than that under single indentation. This phenomenon was possibly caused by defect nucleation and shear accumulation during the holding process, which were promoted by a high holding load. The defect nucleation suppressed the phase transformation from dc-Ge to r8-Ge, and shear accumulation led to another phase transformation pathway, respectively. A high holding load promoted these two phenomena, and thus decreased the possibility of phase transformation from dc-Ge to r8-Ge. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessArticle Morphology Dependent Flow Stress in Nickel-Based Superalloys in the Multi-Scale Crystal Plasticity Framework
Crystals 2017, 7(11), 334; doi:10.3390/cryst7110334
Received: 18 September 2017 / Revised: 19 October 2017 / Accepted: 26 October 2017 / Published: 2 November 2017
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Abstract
This paper develops a framework to obtain the flow stress of nickel-based superalloys as a function of γ-γ’ morphology. The yield strength is a major factor in the design of these alloys. This work provides additional effects of γ’ morphology in the design
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This paper develops a framework to obtain the flow stress of nickel-based superalloys as a function of γ-γ’ morphology. The yield strength is a major factor in the design of these alloys. This work provides additional effects of γ’ morphology in the design scope that has been adopted for the model developed by authors. In general, the two-phase γ-γ’ morphology in nickel-based superalloys can be divided into three variables including γ’ shape, γ’ volume fraction and γ’ size in the sub-grain microstructure. In order to obtain the flow stress, non-Schmid crystal plasticity constitutive models at two length scales are employed and bridged through a homogenized multi-scale framework. The multi-scale framework includes two sub-grain and homogenized grain scales. For the sub-grain scale, a size-dependent, dislocation-density-based finite element model (FEM) of the representative volume element (RVE) with explicit depiction of the γ-γ’ morphology is developed as a building block for the homogenization. For the next scale, an activation-energy-based crystal plasticity model is developed for the homogenized single crystal of Ni-based superalloys. The constitutive models address the thermo-mechanical behavior of nickel-based superalloys for a large temperature range and include orientation dependencies and tension-compression asymmetry. This homogenized model is used to obtain the morphology dependence on the flow stress in nickel-based superalloys and can significantly expedite crystal plasticity FE simulations in polycrystalline microstructures, as well as higher scale FE models in order to cast and design superalloys. Full article
(This article belongs to the Special Issue Crystal Dislocations: Their Impact on Physical Properties of Crystals)
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Open AccessArticle Nanoindentation of HMX and Idoxuridine to Determine Mechanical Similarity
Crystals 2017, 7(11), 335; doi:10.3390/cryst7110335
Received: 28 September 2017 / Revised: 27 October 2017 / Accepted: 28 October 2017 / Published: 1 November 2017
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Abstract
Assessing the mechanical behavior (elastic properties, plastic properties, and fracture phenomena) of molecular crystals is often complicated by the difficulty in preparing samples. Pharmaceuticals and energetic materials in particular are often used in composite structures or tablets, where the individual grains can strongly
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Assessing the mechanical behavior (elastic properties, plastic properties, and fracture phenomena) of molecular crystals is often complicated by the difficulty in preparing samples. Pharmaceuticals and energetic materials in particular are often used in composite structures or tablets, where the individual grains can strongly impact the solid behavior. Nanoindentation is a convenient method to experimentally assess these properties, and it is used here to demonstrate the similarity in the mechanical properties of two distinct systems: individual crystals of the explosive cyclotetramethylene tetranitramine (HMX) and the pharmaceutical idoxuridine were tested in their as-precipitated state, and the effective average modulus and hardness (which can be orientation dependent) were determined. Both exhibit a hardness of 1.0 GPa, with an effective reduced modulus of 25 and 23 GPa for the HMX and idoxuridine, respectively. They also exhibit similar yield point behavior. This indicates idoxuridine may be a suitable mechanical surrogate (or “mock”) for HMX. While the methodology to assess elastic and plastic properties was relatively insensitive to specific crystal orientation (i.e., a uniform distribution in properties was observed for all random crystals tested), the indentation-induced fracture properties appear to be much more sensitive to tip-crystal orientation, and an unloading slope analysis is used to demonstrate the need for further refinement in relating toughness to orientation in these materials with relatively complex slip systems and crystal structures. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessArticle A Novel Dual Air-Bearing Fixed-χ Diffractometer for Small-Molecule Single-Crystal X-ray Diffraction on Beamline I19 at Diamond Light Source
Crystals 2017, 7(11), 336; doi:10.3390/cryst7110336
Received: 17 October 2017 / Revised: 25 October 2017 / Accepted: 29 October 2017 / Published: 2 November 2017
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Abstract
Herein, we describe the development of a novel dual air-bearing fixed-χ diffractometer for beamline I19 at Diamond Light Source. The diffractometer is designed to facilitate the rapid data collections possible with a Dectris Pilatus 2M pixel-array photon-counting detector, while allowing remote operation in
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Herein, we describe the development of a novel dual air-bearing fixed-χ diffractometer for beamline I19 at Diamond Light Source. The diffractometer is designed to facilitate the rapid data collections possible with a Dectris Pilatus 2M pixel-array photon-counting detector, while allowing remote operation in conjunction with a robotic sample changer. The sphere-of-confusion is made as small as practicably possible, through the use of air-bearings for both the ω and φ axes. The design and construction of the new instrument is described in detail and an accompanying paper by Johnson et al. (also in this issue) will provide a user perspective of its operation. Full article
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Open AccessArticle Ultrafast Photoalignment: Recording a Lens in a Nanosecond
Crystals 2017, 7(11), 338; doi:10.3390/cryst7110338
Received: 9 October 2017 / Revised: 31 October 2017 / Accepted: 31 October 2017 / Published: 3 November 2017
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Abstract
Liquid crystals can be photoaligned with a single nanosecond pulse acting on thin photoanisotropic coatings on the cell substrates. This phenomenon was demonstrated for pulses of 532 nm and 355 nm wavelengths (second and the third harmonics of a Nd:YAG laser). Direct printing
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Liquid crystals can be photoaligned with a single nanosecond pulse acting on thin photoanisotropic coatings on the cell substrates. This phenomenon was demonstrated for pulses of 532 nm and 355 nm wavelengths (second and the third harmonics of a Nd:YAG laser). Direct printing of liquid crystal cycloidal diffractive waveplates and diffractive waveplate lenses characterized by high spatial frequencies required only a mJ energy. The liquid crystal alignment dynamics reveal a fast component related to photoalignment of molecules within the photoanisotropic layer and a slower component related to alignment of the liquid crystal within the cell. Full article
(This article belongs to the Special Issue Micro and Nano Patterned Substrates for Liquid Crystal Alignment)
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Open AccessArticle Microindentation Hardness of Protein Crystals under Controlled Relative Humidity
Crystals 2017, 7(11), 339; doi:10.3390/cryst7110339
Received: 9 October 2017 / Revised: 30 October 2017 / Accepted: 31 October 2017 / Published: 4 November 2017
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Abstract
Vickers microindentation hardness of protein crystals was investigated on the (110) habit plane of tetragonal hen egg-white lysozyme crystals containing intracrystalline water at controlled relative humidity. The time evolution of the hardness of the crystals exposed to air with different humidities exhibits three
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Vickers microindentation hardness of protein crystals was investigated on the (110) habit plane of tetragonal hen egg-white lysozyme crystals containing intracrystalline water at controlled relative humidity. The time evolution of the hardness of the crystals exposed to air with different humidities exhibits three stages such as the incubation, transition, and saturation stages. The hardness in the incubation stage keeps a constant value of 16 MPa, which is independent of the humidity. The incubation hardness can correspond to the intrinsic one in the wet condition. The increase of the hardness in the transition and saturation stages is well fitted with the single exponential curve, and is correlated with the reduction of water content in the crystal by the evaporation. The saturated maximum hardness also strongly depends on the water content equilibrated with the humidity. The slip traces corresponding to the (11 ̅0)[110] slip system around the indentation marks are observed in not only incubation but also saturation stages. It is suggested that the plastic deformation in protein crystals by the indentation can be attributed to dislocation multiplication and motion inducing the slip. The indentation hardness in protein crystals is discussed in light of dislocation mechanism with Peierls stress and intracrystalline water. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessArticle The Mixed-Metal Oxochromates(VI) Cd(HgI2)2(HgII)3O4(CrO4)2, Cd(HgII)4O4(CrO4) and Zn(HgII)4O4(CrO4)—Examples of the Different Crystal Chemistry within the Zinc Triad
Crystals 2017, 7(11), 340; doi:10.3390/cryst7110340
Received: 11 October 2017 / Revised: 30 October 2017 / Accepted: 3 November 2017 / Published: 6 November 2017
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Abstract
The three mixed-metal oxochromates(VI) Cd(HgI2)2(HgII)3O4(CrO4)2, Cd(HgII)4O4(CrO4), and Zn(HgII)4O4(CrO4) were grown under hydrothermal
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The three mixed-metal oxochromates(VI) Cd(HgI2)2(HgII)3O4(CrO4)2, Cd(HgII)4O4(CrO4), and Zn(HgII)4O4(CrO4) were grown under hydrothermal conditions. Their crystal structures were determined from single-crystal X-ray diffraction data. The crystal-chemical features of the respective metal cations are characterised, with a linear coordination for mercury atoms in oxidation states +I and +II, octahedral coordination spheres for the divalent zinc and cadmium cations and a tetrahedral configuration of the oxochromate(VI) anions. In the crystal structures the formation of two subunits is apparent, viz. a mercury-oxygen network and a network of cadmium (zinc) cations that are directly bound to the oxochromate(VI) anions. An alternative description of the crystal structures based on oxygen-centred polyhedra is also given. Full article
(This article belongs to the Special Issue Crystal Chemistry of Zinc, Cadmium and Mercury)
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Open AccessArticle Novel Quaternary TlGaSn2Se6 Single Crystal as Promising Material for Laser Operated Infrared Nonlinear Optical Modulators
Crystals 2017, 7(11), 341; doi:10.3390/cryst7110341
Received: 30 September 2017 / Revised: 2 November 2017 / Accepted: 4 November 2017 / Published: 7 November 2017
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Abstract
The studies of the laser operated third order nonlinear optical features of novel TlGaSn2Se6 crystal were done. The main efforts were devoted to a search of a possibility to apply these crystals as laser operated optoelectronic material. For this reason,
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The studies of the laser operated third order nonlinear optical features of novel TlGaSn2Se6 crystal were done. The main efforts were devoted to a search of a possibility to apply these crystals as laser operated optoelectronic material. For this reason, the third harmonic generation of the Nd:YAG pulse laser 1064 nm as the fundamental beam with varied energy density of up to 200 J/m2 was studied. As a source of laser operated light, we have used the cw laser (532 nm), exciting the material above the energy gap. Additionally, the influence of middle-energy Ar+ ions on the XPS spectra of the TlInSn2Se6 surface has been explored. We have shown that the main contribution of the Se4p states is manifested in the upper part of the valence band of TlInSn2Se6 We have established that for the TlGaSn2Se6 crystal there exists a possibility of variation of the third harmonic generation efficiency using illumination by external continuous wave laser beam. The discovered effect makes it possible to utilize TlGaSn2Se6 crystal in advanced optoelectronic laser operated devices. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle Dopant Concentration Induced Optical Changes in Ca,Eu-α-Sialon
Crystals 2017, 7(11), 342; doi:10.3390/cryst7110342
Received: 17 August 2017 / Revised: 1 November 2017 / Accepted: 3 November 2017 / Published: 8 November 2017
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Abstract
The phosphor powders of Ca(m/2)−xEuxSi12−(m+n)Alm+nOnN16−n (m = 1.6, n = 0.8, x in the range of 0–0.08) were synthesized by means of a solid state reaction in flowing nitrogen in a carbon
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The phosphor powders of Ca(m/2)−xEuxSi12−(m+n)Alm+nOnN16−n (m = 1.6, n = 0.8, x in the range of 0–0.08) were synthesized by means of a solid state reaction in flowing nitrogen in a carbon resistant furnace and the influence of Eu concentration on the crystal structure and photoluminescent properties was thoroughly studied. The optical properties of selected α-sialon:Eu2+ samples at temperatures in the range of 10 to 500 K and pressures up to 240 kbar are presented. The crystal lattice parameters were affected by doping with europium and some increase of the unit cell volume was observed up to 6 mol % of Eu. The higher concentration of europium led to subtle changes in the overall structure of the produced sialon phosphors. It was shown that the chemical composition of Ca, Eu-α-sialon phosphor was slightly different from the designed one and the phosphor powders were contaminated by AlN. The phosphor particle surface showed significant europium and oxygen enrichment with Eu3+ but below the thin surface layer Eu2+ was dominant and higher nitrogen content was observed. After examination of absorption, excitation, and emission spectra it was found that the emission peak position shifted toward longer wavelengths with rising Eu2+ concentration from 565 nm (0.1 mol % Eu2+) to 585 nm (10 mol % Eu2+). The quantum yield of the phosphors reached the maximum at a rather low concentration of 4 mol % of Eu. Excitation spectra depend on the monitored wavelength which is typical for multisite Eu2+. The existence of many Eu2+ sites in the sample was supported by the dependence of the decay time on the monitored wavelength. Full article
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Open AccessArticle Expression, Purification, Crystallization, and X-ray Structural Analysis of CRISPR-Associated Protein Cas6 from Methanocaldococcus jannaschii
Crystals 2017, 7(11), 344; doi:10.3390/cryst7110344
Received: 20 September 2017 / Revised: 7 November 2017 / Accepted: 8 November 2017 / Published: 10 November 2017
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Abstract
The CRISPR-associated protein 6, Cas6 protein, is an endoribonuclease that cleaves precursor CRISPR RNAs within the repeat sequence to release specific invader-targeting RNAs. Cas6 protein can recognize different sequences by their specific scaffold. To investigate its binding mode, we purified and crystallized a
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The CRISPR-associated protein 6, Cas6 protein, is an endoribonuclease that cleaves precursor CRISPR RNAs within the repeat sequence to release specific invader-targeting RNAs. Cas6 protein can recognize different sequences by their specific scaffold. To investigate its binding mode, we purified and crystallized a His-tagged Cas6 protein from Methanocaldococcus jannaschii (MjCas6) using the sitting-drop vapor-diffusion method. The crystals diffracted to a resolution of 1.85 Å and belonged to monoclinic space group C2, with unit-cell parameters a = 200.84 Å, b = 85.26 Å, c = 100.06 Å, β = 118.47°. The crystals of MjCas6 contain four molecules in the asymmetric unit. The protein fold is similar to the other Cas6 homologues, such as Pyrococcus furiosus Cas6, suggesting functional similarity. Moreover, in the C2 crystal the MjCas6 monomers formed a tandem array, which we hypothesize to possibly correlate with repetitive RNA precursors. Full article
(This article belongs to the Special Issue Recent Advances in Protein Crystallography)
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Open AccessArticle Galloping Reduction of Transmission Lines by Using Phononic Crystal
Crystals 2017, 7(11), 346; doi:10.3390/cryst7110346
Received: 2 November 2017 / Accepted: 10 November 2017 / Published: 13 November 2017
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Abstract
Considering the combination of the transmission lines and phononic crystals (PCs), we propose a new method to solve the problem of the galloping of overhead transmission lines. The method has two key points: attaching the suitable mass-spring system on each spacer, and periodically
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Considering the combination of the transmission lines and phononic crystals (PCs), we propose a new method to solve the problem of the galloping of overhead transmission lines. The method has two key points: attaching the suitable mass-spring system on each spacer, and periodically arranging the modified spacers along a transmission line. Based on the Bloch’s theorem, the PC transmission lines could generate vibration band gaps (BGs), which would reduce galloping. In order to implement our point, we establish the two-dimensional model of the PC transmission lines and derive the transfer matrix method to calculate the frequency dispersion relation of the vertical transverse vibration. Then, the extremely low frequency BG, in the range of galloping frequency, is obtained and verified based on an example of single conductor. To widen the BG range, we also study the effects of the spacer and the attached mass-spring system on the BG. The wide BG, which even covers the range of 0.338–0.909 Hz, could be given just by using the suitable setting of the spacer and mass-spring system. Full article
(This article belongs to the Special Issue Phononics)
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Open AccessArticle Quantitative Imaging of the Stress/Strain Fields and Generation of Macroscopic Cracks from Indents in Silicon
Crystals 2017, 7(11), 347; doi:10.3390/cryst7110347
Received: 10 October 2017 / Revised: 7 November 2017 / Accepted: 8 November 2017 / Published: 14 November 2017
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Abstract
The crack geometry and associated strain field around Berkovich and Vickers indents on silicon have been studied by X-ray diffraction imaging and micro-Raman spectroscopy scanning. The techniques are complementary; the Raman data come from within a few micrometres of the indentation, whereas the
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The crack geometry and associated strain field around Berkovich and Vickers indents on silicon have been studied by X-ray diffraction imaging and micro-Raman spectroscopy scanning. The techniques are complementary; the Raman data come from within a few micrometres of the indentation, whereas the X-ray image probes the strain field at a distance of typically tens of micrometres. For example, Raman data provide an explanation for the central contrast feature in the X-ray images of an indent. Strain relaxation from breakout and high temperature annealing are examined and it is demonstrated that millimetre length cracks, similar to those produced by mechanical damage from misaligned handling tools, can be generated in a controlled fashion by indentation within 75 micrometres of the bevel edge of 200 mm diameter wafers. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessArticle Design and Fabrication Challenges for Millimeter-Scale Three-Dimensional Phononic Crystals
Crystals 2017, 7(11), 348; doi:10.3390/cryst7110348
Received: 16 October 2017 / Revised: 9 November 2017 / Accepted: 11 November 2017 / Published: 15 November 2017
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Abstract
While phononic crystals can be theoretically modeled with a variety of analytical and numerical methods, the practical realization and comprehensive characterization of complex designs is often challenging. This is especially important for the nearly limitless possibilities of periodic, three-dimensional structures. In this contribution,
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While phononic crystals can be theoretically modeled with a variety of analytical and numerical methods, the practical realization and comprehensive characterization of complex designs is often challenging. This is especially important for the nearly limitless possibilities of periodic, three-dimensional structures. In this contribution, we take a look at these design and fabrication challenges of different 3D phononic elements based on recent research using additive manufacturing. Different fabrication technologies introduce specific limitations in terms of, e.g., material choices, minimum feature size, aspect ratios, or support requirements that have to be taken into account during design and theoretical modeling. We discuss advantages and disadvantages of additive technologies suitable for millimeter and sub-millimeter feature sizes. Furthermore, we present comprehensive experimental characterization of finite, simple cubic lattices in terms of wave polarization and propagation direction to demonstrate the substantial differences between complete phononic band gap and application oriented directional band gaps of selected propagation modes. Full article
(This article belongs to the Special Issue Phononics)
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Open AccessArticle Effects of Thermal Annealing on the Properties of Mechanically Exfoliated Suspended and On-Substrate Few-Layer Graphene
Crystals 2017, 7(11), 349; doi:10.3390/cryst7110349
Received: 25 October 2017 / Revised: 11 November 2017 / Accepted: 13 November 2017 / Published: 15 November 2017
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Abstract
Graphene’s novel electrical, optical, and mechanical properties are affected both by substrate interaction and processing steps required to fabricate contacts and devices. Annealing is used to clean graphene devices, but this can lead to doping and defect changes and strain effects. There is
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Graphene’s novel electrical, optical, and mechanical properties are affected both by substrate interaction and processing steps required to fabricate contacts and devices. Annealing is used to clean graphene devices, but this can lead to doping and defect changes and strain effects. There is often disagreement about which of these effects are occurring and which result in observed changes in Raman spectra. The effects of vacuum annealing on mechanically exfoliated pristine, suspended, and attached thin and thick few-layer graphene on SiO2/Si are investigated here using scanning electron microscopy (SEM), Raman spectroscopy, and atomic force microscopy (AFM). Before annealing, Raman shows that the differences in 2D and G band positions and the appearance of a disorder-induced D band of all regions were mainly because of compressive or tensile structural deformations emerging through mechanical exfoliation instead of charge doping. Annealing at low temperature is sufficient to eliminate most of the defects. However, compressive strain is induced in the sheet by annealing at high temperature, and for thin regions increased substrate conformation leads to the apparent disappearance of the sheets. The intensity ratio of the 2D and G bands also reduces with induced compressive strain, and thus should not be used to detect doping. Full article
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Open AccessArticle Simultaneous Guidance of Surface Acoustic and Surface Optical Waves in Phoxonic Crystal Slabs
Crystals 2017, 7(11), 350; doi:10.3390/cryst7110350
Received: 15 October 2017 / Revised: 5 November 2017 / Accepted: 15 November 2017 / Published: 19 November 2017
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Abstract
Phoxonic crystals, which exhibit simultaneous phononic and photonic bandgaps, are promising artificial materials for optomechanical and acousto-optical devices. In this paper, simultaneous guidance of surface acoustic and surface optical waves in truncated phoxonic crystal slabs with veins is investigated using the finite element
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Phoxonic crystals, which exhibit simultaneous phononic and photonic bandgaps, are promising artificial materials for optomechanical and acousto-optical devices. In this paper, simultaneous guidance of surface acoustic and surface optical waves in truncated phoxonic crystal slabs with veins is investigated using the finite element method. The phoxonic crystal slabs with veins can show dual large bandgaps of phononic and photonic even/odd modes. Based on the phononic and photonic bandgaps, simultaneous surface acoustic and optical modes can be realized by changing the surface geometrical configurations. Both acoustic and optical energies can be highly confined in the surface region. The effect of the surface structures on the dispersion relations of surface modes is discussed; by adjusting the surface geometrical parameters, dual single guided modes and/or slow acoustic and optical waves with small group velocity dispersions can be achieved. The group velocities are about 40 and 10 times smaller than the transverse velocity of the elastic waves in silicon and the speed of light in vacuum, respectively. Full article
(This article belongs to the Special Issue Phononics)
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Open AccessArticle Room-Temperature Plastic Deformation of Strontium Titanate Crystals Grown from Different Chemical Compositions
Crystals 2017, 7(11), 351; doi:10.3390/cryst7110351
Received: 11 October 2017 / Revised: 17 November 2017 / Accepted: 21 November 2017 / Published: 22 November 2017
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Abstract
Oxide materials have the potential to exhibit superior mechanical properties in terms of high yield point, high melting point, and high chemical stability. Despite this, they are not widely used as a structural material due to their brittle nature. However, this study shows
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Oxide materials have the potential to exhibit superior mechanical properties in terms of high yield point, high melting point, and high chemical stability. Despite this, they are not widely used as a structural material due to their brittle nature. However, this study shows enhanced room-temperature plasticity of strontium titanate (SrTiO3) crystals through the control of the chemical composition. It is shown that the deformation behavior of SrTiO3 crystals at room temperature depends on the Sr/Ti ratio. It was found that flow stresses in deforming SrTiO3 crystals grown from a powder with the particular ratio of Sr/Ti = 1.04 are almost independent of the strain rate because of the high mobility of dislocations in such crystals. As a result, the SrTiO3 crystals can deform by dislocation slip up to a strain of more than 10%, even at a very high strain rate of 10% per second. It is thus demonstrated that SrTiO3 crystals can exhibit excellent plasticity when chemical composition in the crystal is properly controlled. Full article
(This article belongs to the Special Issue Crystal Dislocations: Their Impact on Physical Properties of Crystals)
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Review

Jump to: Research

Open AccessReview Indentation Plasticity and Fracture Studies of Organic Crystals
Crystals 2017, 7(11), 324; doi:10.3390/cryst7110324
Received: 23 September 2017 / Revised: 18 October 2017 / Accepted: 23 October 2017 / Published: 27 October 2017
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Abstract
This review article summarizes the recent advances in measuring and understanding the indentation-induced plastic deformation and fracture behavior of single crystals of a wide variety of organic molecules and pharmaceutical compounds. The importance of hardness measurement for molecular crystals at the nanoscale, methods
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This review article summarizes the recent advances in measuring and understanding the indentation-induced plastic deformation and fracture behavior of single crystals of a wide variety of organic molecules and pharmaceutical compounds. The importance of hardness measurement for molecular crystals at the nanoscale, methods and models used so far to analyze and estimate the hardness of the crystals, factors affecting the indentation hardness of organic crystals, correlation of the mechanical properties to their underlying crystal packing, and fracture toughness studies of molecular crystals are reviewed. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessReview Formation of Metastable Crystals from Supercooled, Supersaturated, and Supercompressed Liquids: Role of Crystal-Liquid Interfacial Free Energy
Crystals 2017, 7(11), 326; doi:10.3390/cryst7110326
Received: 28 July 2017 / Revised: 19 October 2017 / Accepted: 26 October 2017 / Published: 29 October 2017
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Abstract
The formation mechanism of metastable crystals from metastable liquids still remains elusive, although controlling the metastability of crystals and liquids already plays a crucial role in designing new materials in physics, chemistry, biology, and materials science. This review article describes how metastable phases
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The formation mechanism of metastable crystals from metastable liquids still remains elusive, although controlling the metastability of crystals and liquids already plays a crucial role in designing new materials in physics, chemistry, biology, and materials science. This review article describes how metastable phases can be obtained by controlling temperature, concentration, and pressure. In particular, I show the role of crystal-liquid interfacial free energy in the formation of metastable crystals from metastable liquids at a given driving force. In a microscopic viewpoint, local structure similarity between the metastable crystals and liquid determines the crystal-liquid interfacial free energy, and thus the nucleation barrier for the metastable crystals. The effect of the interfacial free energy on the formation of metastable crystals from supercooled, supersaturated, and supercompressed liquids will be demonstrated with metallic liquids, aqueous solutions, and water. Full article
(This article belongs to the Special Issue Crystal Formation from Metastable Liquids)
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Open AccessReview Brief Review of Epitaxy and Emission Properties of GaSb and Related Semiconductors
Crystals 2017, 7(11), 337; doi:10.3390/cryst7110337
Received: 31 August 2017 / Revised: 22 October 2017 / Accepted: 25 October 2017 / Published: 2 November 2017
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Abstract
Groups III–V semiconductors have received a great deal of attention because of their potential advantages for use in optoelectronic and electronic applications. Gallium antimonide (GaSb) and GaSb-related semiconductors, which exhibit high carrier mobility and a narrow band gap (0.725 eV at 300 K),
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Groups III–V semiconductors have received a great deal of attention because of their potential advantages for use in optoelectronic and electronic applications. Gallium antimonide (GaSb) and GaSb-related semiconductors, which exhibit high carrier mobility and a narrow band gap (0.725 eV at 300 K), have been recognized as suitable candidates for high-performance optoelectronics in the mid-infrared range. However, the performances of the resulting devices are strongly dependent on the structural and emission properties of the materials. Enhancement of the crystal quality, adjustment of the alloy components, and improvement of the emission properties have therefore become the focus of research efforts toward GaSb semiconductors. Molecular beam epitaxy (MBE) is suitable for the large-scale production of GaSb, especially for high crystal quality and beneficial optical properties. We review the recent progress in the epitaxy of GaSb materials, including films and nanostructures composed of GaSb-related alloys and compounds. The emission properties of these materials and their relationships to the alloy components and material structures are also discussed. Specific examples are included to provide insight on the common general physical and optical properties and parameters involved in the synergistic epitaxy processes. In addition, the further directions for the epitaxy of GaSb materials are forecasted. Full article
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Open AccessReview Biomineralization Mediated by Ureolytic Bacteria Applied to Water Treatment: A Review
Crystals 2017, 7(11), 345; doi:10.3390/cryst7110345
Received: 6 October 2017 / Revised: 2 November 2017 / Accepted: 4 November 2017 / Published: 17 November 2017
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Abstract
The formation of minerals such as calcite and struvite through the hydrolysis of urea catalyzed by ureolytic bacteria is a simple and easy way to control mechanisms, which has been extensively explored with promising applications in various areas such as the improvement of
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The formation of minerals such as calcite and struvite through the hydrolysis of urea catalyzed by ureolytic bacteria is a simple and easy way to control mechanisms, which has been extensively explored with promising applications in various areas such as the improvement of cement and sandy materials. This review presents the detailed mechanism of the biominerals production by ureolytic bacteria and its applications to the wastewater, groundwater and seawater treatment. In addition, an interesting application is the use of these ureolytic bacteria in the removal of heavy metals and rare earths from groundwater, the removal of calcium and recovery of phosphate from wastewater, and its potential use as a tool for partial biodesalination of seawater and saline aquifers. Finally, we discuss the benefits of using biomineralization processes in water treatment as well as the challenges to be solved in order to reach a successful commercialization of this technology. Full article
(This article belongs to the Special Issue Biological and Biogenic Crystallization)
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