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Crystals, Volume 10, Issue 7 (July 2020) – 57 articles

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Open AccessArticle
Effect of Stacking Fault Energy on Microstructure and Texture Evolution during the Rolling of Non-Equiatomic CrMnFeCoNi High-Entropy Alloys
Crystals 2020, 10(7), 607; https://doi.org/10.3390/cryst10070607 (registering DOI) - 13 Jul 2020
Abstract
The evolution of microstructure and texture in three non-equiatomic CrMnFeCoNi high-entropy alloys (HEAs) with varying stacking fault energy (SFE) has been studied in up to 90% rolling reductions at both room and cryogenic temperature. All the HEAs deform by dislocation slip and additional [...] Read more.
The evolution of microstructure and texture in three non-equiatomic CrMnFeCoNi high-entropy alloys (HEAs) with varying stacking fault energy (SFE) has been studied in up to 90% rolling reductions at both room and cryogenic temperature. All the HEAs deform by dislocation slip and additional mechanical twinning at intermediate and shear banding at high rolling strains. The microstructure is quite heterogeneous and, with strain, becomes highly fragmented. During rolling, a characteristic brass-type texture develops. Its strength increases with a decreasing SFE and the lowering of the rolling temperature. The texture evolution is discussed with regard to planar slip, mechanical twinning, and shear banding. Full article
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Open AccessReview
The Solid-State Structures of Cyclic NH Carboximides
Crystals 2020, 10(7), 606; https://doi.org/10.3390/cryst10070606 (registering DOI) - 12 Jul 2020
Viewed by 173
Abstract
The patterns adopted in the solid state structures of over 300 cyclic NH carboximides as determined by X-ray diffraction are reviewed. While the analysis shows that the majority of these fit into just a few common patterns, a significant number exhibit more complex [...] Read more.
The patterns adopted in the solid state structures of over 300 cyclic NH carboximides as determined by X-ray diffraction are reviewed. While the analysis shows that the majority of these fit into just a few common patterns, a significant number exhibit more complex and interesting patterns involving the other functional groups present in addition to the cyclic imide. Full article
(This article belongs to the Special Issue Analysis of Hydrogen Bonds in Crystals)
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Open AccessArticle
Ideal Photonic Weyl Nodes Stabilized by Screw Rotation Symmetry in Space Group 19
Crystals 2020, 10(7), 605; https://doi.org/10.3390/cryst10070605 (registering DOI) - 12 Jul 2020
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Abstract
Topological photonics have developed in recent years since the seminal discoveries of topological insulators in condensed matter physics for electrons. Among the numerous studies, photonic Weyl nodes have been studied very recently due to their intriguing surface Fermi arcs, Chiral zero modes and [...] Read more.
Topological photonics have developed in recent years since the seminal discoveries of topological insulators in condensed matter physics for electrons. Among the numerous studies, photonic Weyl nodes have been studied very recently due to their intriguing surface Fermi arcs, Chiral zero modes and scattering properties. In this article, we propose a new design of an ideal photonic Weyl node metacrystal, meaning no excessive states are present at the Weyl nodes’ frequency. The Weyl node is stabilized by the screw rotation symmetry of space group 19. Group theory analysis is utilized to reveal how the Weyl nodes are spawned from line nodes in a higher symmetry metacrystal of space group 61. The minimum four Weyl nodes’ complex for time reversal invariant systems is found, which is a realistic photonic Weyl node metacrystal design compatible with standard printed circuit board techniques and is a complement to the few existing ideal photonic Weyl node designs and could be further utilized in studies of Weyl physics, for instance, Chiral zero modes and scatterings. Full article
(This article belongs to the Special Issue Advances in Topological Materials)
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Open AccessReview
Novel Trends in Lyotropic Liquid Crystals
Crystals 2020, 10(7), 604; https://doi.org/10.3390/cryst10070604 (registering DOI) - 12 Jul 2020
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Abstract
We introduce and shortly summarize a variety of more recent aspects of lyotropic liquid crystals (LLCs), which have drawn the attention of the liquid crystal and soft matter community and have recently led to an increasing number of groups studying this fascinating class [...] Read more.
We introduce and shortly summarize a variety of more recent aspects of lyotropic liquid crystals (LLCs), which have drawn the attention of the liquid crystal and soft matter community and have recently led to an increasing number of groups studying this fascinating class of materials, alongside their normal activities in thermotopic LCs. The diversity of topics ranges from amphiphilic to inorganic liquid crystals, clays and biological liquid crystals, such as viruses, cellulose or DNA, to strongly anisotropic materials such as nanotubes, nanowires or graphene oxide dispersed in isotropic solvents. We conclude our admittedly somewhat subjective overview with materials exhibiting some fascinating properties, such as chromonics, ferroelectric lyotropics and active liquid crystals and living lyotropics, before we point out some possible and emerging applications of a class of materials that has long been standing in the shadow of the well-known applications of thermotropic liquid crystals, namely displays and electro-optic devices. Full article
(This article belongs to the Special Issue New Trends in Lyotropic Liquid Crystals)
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Open AccessArticle
Synthesis and Characterization of Photoluminescence Liquid Crystals Based on Flexible Chain-Bearing Pentafluorinated Bistolanes
Crystals 2020, 10(7), 603; https://doi.org/10.3390/cryst10070603 (registering DOI) - 11 Jul 2020
Viewed by 202
Abstract
The liquid-crystalline (LC) and photophysical properties of molecules are very sensitive to their electronic and molecular aggregate structures. Herein, to shed light on the structure–property relationships of pentafluorinated bistolane-based photoluminescence (PL) liquid crystals (PLLCs) previously reported by our group, we synthesized pentafluorinated bistolanes [...] Read more.
The liquid-crystalline (LC) and photophysical properties of molecules are very sensitive to their electronic and molecular aggregate structures. Herein, to shed light on the structure–property relationships of pentafluorinated bistolane-based photoluminescence (PL) liquid crystals (PLLCs) previously reported by our group, we synthesized pentafluorinated bistolanes with variable flexible chains and evaluated their LC and photophysical properties. The incorporation of an oxygen atom (to afford a 2-methoxyethoxy unit) or an oxygen atom and a methyl group (to afford a 1-methoxyprop-2-oxy unit) into the flexible butoxy chain significantly decreased the temperature of the crystalline-to-LC phase transition, and a chiral nematic phase comprising helical molecular aggregates was observed for the chiral 1-methoxyprop-2-oxy group–bearing bistolane. The synthesized bistolanes exhibited strong blue PL in both solution and crystalline phases; the featuring PL characteristics were maintained in the LC phase (produced by the crystalline-to-LC phase transition) except for a slight PL color change. Thus, it was concluded that the PL behavior of pentafluorinated bistolanes can be modulated by the choice of a suitable flexible chain, and the obtained insights are believed to facilitate the application of PLLCs in thermosensing PL materials. Full article
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Open AccessReview
Layered Double Hydroxides in Bioinspired Nanotechnology
Crystals 2020, 10(7), 602; https://doi.org/10.3390/cryst10070602 (registering DOI) - 11 Jul 2020
Viewed by 146
Abstract
Layered Double Hydroxides (LDHs) are a relevant class of inorganic lamellar nanomaterials that have attracted significant interest in life science-related applications, due to their highly controllable synthesis and high biocompatibility. Under a general point of view, this class of materials might have played [...] Read more.
Layered Double Hydroxides (LDHs) are a relevant class of inorganic lamellar nanomaterials that have attracted significant interest in life science-related applications, due to their highly controllable synthesis and high biocompatibility. Under a general point of view, this class of materials might have played an important role for the origin of life on planet Earth, given their ability to adsorb and concentrate life-relevant molecules in sea environments. It has been speculated that the organic–mineral interactions could have permitted to organize the adsorbed molecules, leading to an increase in their local concentration and finally to the emergence of life. Inspired by nature, material scientists, engineers and chemists have started to leverage the ability of LDHs to absorb and concentrate molecules and biomolecules within life-like compartments, allowing to realize highly-efficient bioinspired platforms, usable for bioanalysis, therapeutics, sensors and bioremediation. This review aims at summarizing the latest evolution of LDHs in this research field under an unprecedented perspective, finally providing possible challenges and directions for future research. Full article
(This article belongs to the Special Issue Layered Double Hydroxides)
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Open AccessArticle
Carbon Nanotube Detectors and Spectrometers for the Terahertz Range
Crystals 2020, 10(7), 601; https://doi.org/10.3390/cryst10070601 - 10 Jul 2020
Viewed by 156
Abstract
We present the compact unified charge control model (UCCM) for carbon nanotube field-effect transistors (CNTFETs) to enable the accurate simulation of the DC characteristics and plasmonic terahertz (THz) response in the CNTFETs. Accounting for the ambipolar nature of the carrier transport (n-type and [...] Read more.
We present the compact unified charge control model (UCCM) for carbon nanotube field-effect transistors (CNTFETs) to enable the accurate simulation of the DC characteristics and plasmonic terahertz (THz) response in the CNTFETs. Accounting for the ambipolar nature of the carrier transport (n-type and p-type conductivity at positive and negative gate biases, respectively), we use n-type and p-type CNTFET non-linear equivalent circuits connected in parallel, representing the ambipolar conduction in the CNTFETs. This allows us to present a realistic non-linear model that is valid across the entire voltage range and is therefore suitable for the CNTFET design. The important feature of the model is that explicit equations for gate bias, current, mobility, and capacitance with smoothing parameters accurately describe the device operation near the transition from above- to below-threshold regimes, with scalability in device geometry. The DC performance in the proposed compact CNTFET model is validated by the comparison between the SPICE simulation and the experimental DC characteristics. The simulated THz response resulted from the validated CNTFET model is found to be in good agreement with the analytically calculated response and also reveals the bias and power dependent sub-THz response and relatively wide dynamic range for detection that could be suitable for THz detectors. The operation of CNTFET spectrometers in the THz frequency range is further demonstrated using the present model. The simulation exhibits that the CNT-based spectrometers can cover a broad THz frequency band from 0.1 to 3.08 THz. The model that has been incorporated into the circuit simulators enables the accurate assessment of DC performance and THz operation. Therefore, it can be used for the design and performance estimation of the CNTFETs and their integrated circuits operating in the THz regime. Full article
(This article belongs to the Special Issue Plasmonic Nanostructures)
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Open AccessArticle
N-Acetyl Indole Linked to a Fused Triazolo/Thiadiazole Scaffold: Synthesis, Single Crystal X-Ray Structure, and Molecular Insight
Crystals 2020, 10(7), 600; https://doi.org/10.3390/cryst10070600 - 10 Jul 2020
Viewed by 157
Abstract
The designed target compound of N-acetyl indole linked to a fused triazolo/thiadiazole scaffold was synthesized via the reaction of 4-amino-5-(1H-indol-2-yl)-1,2,4-triazol-3(2H)-thione as the starting material with acetic anhydride under reflux conditions for 6 h, resulting in an excellent and pure chemical yield. The structural [...] Read more.
The designed target compound of N-acetyl indole linked to a fused triazolo/thiadiazole scaffold was synthesized via the reaction of 4-amino-5-(1H-indol-2-yl)-1,2,4-triazol-3(2H)-thione as the starting material with acetic anhydride under reflux conditions for 6 h, resulting in an excellent and pure chemical yield. The structural features of the designed compound were confirmed using spectroscopic tools including single crystal X-ray diffraction analysis along with 1H-NMR, 13C-NMR, 2D-NMR, and high resolution mass spectrometry. Using Hirshfeld analysis, we determined the molecular packing depends on strong interactions (O···H and N···H) along with weak interactions (S···H, C···H and H···H). The shortest contacts corresponding to the N3···H12 (2.490 Å), N2···H5 (2.503 Å), and O1···H2 (2.490 Å) interactions were confirmed based on the Hirshfeld analysis. The calculated dipole moment was 6.6557 Debye. The atomic charge distribution, molecular electrostatic potential map, and reactivity descriptors are also discussed. The computed NMR spectra of the requisite compound correlated well with the results obtained experimentally. The UV-Vis electronic spectra of the requisite compound were simulated using the TD-DFT method and compared with the experimental data. The different σ→σ*, π→π*, n→σ*, and n→π* donor–acceptor interactions and their interaction energies stabilized the studied system to 9.84, 20.65, 29.33, and 45.82 kcal/mol, respectively. Full article
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Open AccessArticle
Water Based Synthesis of ZIF-8 Assisted by Hydrogen Bond Acceptors and Enhancement of CO2 Uptake by Solvent Assisted Ligand Exchange
Crystals 2020, 10(7), 599; https://doi.org/10.3390/cryst10070599 - 10 Jul 2020
Viewed by 148
Abstract
The aim of this work was to synthesize zeolitic imidazolate framework-8 (ZIF-8) by an alternative method and then modify the surface properties for enhancing the CO2 adsorption performance. The ZIF-8 was synthesized by a water based synthesis method using 2-methyl imidazole (2-MeIM) [...] Read more.
The aim of this work was to synthesize zeolitic imidazolate framework-8 (ZIF-8) by an alternative method and then modify the surface properties for enhancing the CO2 adsorption performance. The ZIF-8 was synthesized by a water based synthesis method using 2-methyl imidazole (2-MeIM) as a hydrogen bond donor and quaternary ammonium salts (QAS) as a hydrogen bond acceptor. The optimal synthesis conditions were investigated by varying (i) the order of precursor mixing during the synthesis process (ii) different QAS (tetrabutyl ammonium bromide (TBAB), tetraethyl ammonium bromide (TEAB) and trimethyl phenyl ammonium bromide (TMPAB)) and (iii) the ratio between 2-MeIM and QAS. The results show that the optimal synthesis condition was using TMPAB as the hydrogen bond acceptor with the ratio between 2-MeIM and TMPAB of 8:2 and in the order of first mixing both hydrogen bond donor and acceptor before adding Zn(NO3)2⋅6H2O solution. TMPAB can provide uniform size distribution with the smallest particle sizes of ZIF-8. This can be explained by the higher hydrogen bond strength between hydrogen bond donor (2-MeIM) and hydrogen bond acceptor (TMPAB) when compared with that of the rest of two QAS. The synthesized ZIF-8 was modified by solvent-assisted ligand exchange methods. The organic linker of ZIF-8 (2-MeIM) was exchanged by 2-aminobenzimidazole (2-NH2bZIM) and 2-phenylimidazole (2-PhIM). The CO2 uptake of modified ZIF-8 was enhanced upon exchanging with 2-NH2bZIM. The increase in CO2 uptake was due to an additional interaction between CO2 and exchanged imidazole linker and an increase in surface properties (higher surface area, pore size and pore volume). Full article
(This article belongs to the Special Issue Structure and Properties of Inorganic Nanoparticles)
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Open AccessArticle
Numerical Simulation of Ice Fractures Process of the Yellow River Based on Disk Specimen
Crystals 2020, 10(7), 598; https://doi.org/10.3390/cryst10070598 - 10 Jul 2020
Viewed by 163
Abstract
To study the influence of the changes in crystals on a micro scale as well as their effect on the macro mechanical properties of river ice and to mitigate the limitation of the objective conditions in a physical examination of river ice, it [...] Read more.
To study the influence of the changes in crystals on a micro scale as well as their effect on the macro mechanical properties of river ice and to mitigate the limitation of the objective conditions in a physical examination of river ice, it is necessary to analyze the fracture process of river ice using a micro numerical calculation method. Thus, a numerical model was established to simulate the cracking process of river ice based on disk specimen. Upon comparison with the physical experiment, the results of the numerical model show agreement with the fracture toughness and cracking process. Based on the numerical model, the obtained material parameters of Yellow River ice laid a foundation for the study of the cracking process of river ice on a macro-, meso-, and multiscale. Full article
(This article belongs to the Special Issue Ice Crystals (Volume II))
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Open AccessRetraction
Retraction: Leong, W.S.; Arrabito, G.; Prestopino, G. Artificial Intelligence Algorithm Enabled Industrial-Scale Graphene Characterization. Crystals 2020, 10, 308
Crystals 2020, 10(7), 597; https://doi.org/10.3390/cryst10070597 - 10 Jul 2020
Viewed by 139
Abstract
The Crystals Editorial Office has been made aware that the data and results in this published paper [...] Full article
Open AccessCommunication
Feasibility Study of Selective Laser Melting for Metal Matrix Diamond Tools
Crystals 2020, 10(7), 596; https://doi.org/10.3390/cryst10070596 - 10 Jul 2020
Viewed by 176
Abstract
Metal matrix diamond composite samples were fabricated by selective laser melting (SLM) at different forming parameters to investigate the feasibility and new challenges when SLM is applied to diamond tools manufacturing. The surface topographies, Rockwell hardness, compactness, microstructure, and diamond thermal damage of [...] Read more.
Metal matrix diamond composite samples were fabricated by selective laser melting (SLM) at different forming parameters to investigate the feasibility and new challenges when SLM is applied to diamond tools manufacturing. The surface topographies, Rockwell hardness, compactness, microstructure, and diamond thermal damage of the samples were investigated in this study. The fabricated samples had high porosity and relatively low Rockwell hardness and compactness, and some ridge-shaped bulges and textures were observed at the edges and surfaces. Microstructure analyses showed that diamond particles were homogeneously distributed and metallurgically bonded within the metal matrix. The thermal damage pits on the diamond crystals along the scanning direction were the dominant damage type for SLM, which was completely different from conventional vacuum brazing and hot-pressing sintering. Although some challenges need to be further studied, our results demonstrate that SLM has great potential to propel the development of metal matrix diamond tools. Full article
(This article belongs to the Special Issue Diamond Crystals Volume II)
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Open AccessEditorial
Pressure-Induced Phase Transformations
Crystals 2020, 10(7), 595; https://doi.org/10.3390/cryst10070595 - 10 Jul 2020
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Abstract
The study of phase transitions in solids under high pressure conditions is a very active and vigorous research field [...] Full article
(This article belongs to the Special Issue Pressure-Induced Phase Transformations)
Open AccessArticle
Effect of Silver Nanoparticles on the Melting Behavior, Isothermal Crystallization Kinetics and Morphology of Polyoxymethylene
Crystals 2020, 10(7), 594; https://doi.org/10.3390/cryst10070594 - 09 Jul 2020
Viewed by 216
Abstract
In this work, the effects of silver (Ag) nanoparticles on the melting behavior, isothermal crystallization kinetics, and morphology of polyoxymethylene (POM) were studied. It was found that the melting peak temperature (Tm) and the crystallization temperature (TC) [...] Read more.
In this work, the effects of silver (Ag) nanoparticles on the melting behavior, isothermal crystallization kinetics, and morphology of polyoxymethylene (POM) were studied. It was found that the melting peak temperature (Tm) and the crystallization temperature (TC) of POM/Ag nanocomposites shifted to higher temperature with the content of Ag nanoparticles increased. In addition, the isothermal crystallization kinetics of POM/Ag nanocomposites were determined by Avrami and Lauritzen-Hoffman models. The results of crystallization half-time (t0.5), reciprocal of crystallization half-time (τ0.5), Avrami exponent (n), and Avrami rate constant (k) showed that low loading of Ag nanoparticles (≤1 wt%) accelerated the crystallization rate of POM. However, when the content of Ag nanoparticles reached 2 wt%, they aggregated together and restrained crystallization of POM. Meanwhile, the results of nucleation parameter (Kg) and surface free energy of folding (δe) revealed that Ag nanoparticles reduced the energy need to create a new crystal surface, leading to faster crystallization. Moreover, the crystallization activation energies (∆E) were determined using the Arrhenius model, which suggested that Ag nanoparticles induced the heterogeneous nucleation by lowing the ∆E. Furthermore, polarized light microscopy results indicated Ag nanoparticles generated a great amount of nucleation sites and led to the formation of smaller spherulites. Full article
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Open AccessArticle
Library of UV-Visible Absorption Spectra of Rare Earth Orthophosphates, LnPO4 (Ln = La-Lu, except Pm)
Crystals 2020, 10(7), 593; https://doi.org/10.3390/cryst10070593 - 09 Jul 2020
Viewed by 219
Abstract
In recent times, rare earth orthophosphates ( L n PO 4 ) have shown great potential as efficient optical materials. They possess either m o n a z i t e or x e n o t i m e –type structures. These [...] Read more.
In recent times, rare earth orthophosphates ( L n PO 4 ) have shown great potential as efficient optical materials. They possess either m o n a z i t e or x e n o t i m e –type structures. These light or heavy rare earth bearing orthophosphates also exhibit an extraordinary stability over geological time scale in nature, ∼10 9 years. In the present contribution, we measure, collect, and present a library of absorption spectra of all the L n PO 4 hosts ( L n = La–Lu, except Pm) using their single crystal samples, to conclude that the observed spectral features for wavelengths longer than 200 nm were attributable to either Ln- or defect related centers, which corroborate the fact that they have a bandgap higher than 8.0 eV. The absorption band around wavelength, 275 nm, corresponds to defect absorption related to PO 3 centers and/or oxygen vacancies. The hosts can potentially be used to study and interpret unperturbed rare earth emissions due to absence of host related absorption above 300 nm. The information presented herein is expected to serve as a library of absorption spectra for geologists, physicists, material scientists, and chemists working in the field of rare earths. Full article
(This article belongs to the Special Issue Transparent Glass Ceramics)
Open AccessArticle
Formation of Tetranuclear Nickel(II) Complexes with Schiff-Bases: Crystal Structures and Magnetic Properties
Crystals 2020, 10(7), 592; https://doi.org/10.3390/cryst10070592 - 09 Jul 2020
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Abstract
The cubane-type structure is a typical representative of tetranuclear coordination compounds. In this work, two anionic Schiff-base ligands, (L1)2− and (L2)2−, each offering an O^N^O coordination pocket, ligate four NiII ions into a [Ni4 [...] Read more.
The cubane-type structure is a typical representative of tetranuclear coordination compounds. In this work, two anionic Schiff-base ligands, (L1)2− and (L2)2−, each offering an O^N^O coordination pocket, ligate four NiII ions into a [Ni4O4] cubane core. The ligands are H2L1 = 2−[[(3-ethoxy-2−hydroxyphenyl) methylene]amino]benzenemethanol and H2L2 = 2−[[(5-fluoro-2−hydroxyphenyl)methylene]amino]benzenemethanol. In both compounds, [Ni4(L1)4(EtOH)4] (1) and [Ni4(L2)4(MeOH)4] (2), alkoxy oxygens of the ligands act in a bridging μ3-O binding mode. Magnetic susceptibility and magnetization data for compounds 1 and 2 are presented. The Ni–O–Ni bond angles of the cubane core determined from single crystal X-ray diffraction data play a key role for a magneto-structural correlation. Dominant intracube ferromagnetic behavior is observed, and the coupling parameters were determined for both compounds, leading to nonzero spin ground states in accordance with the broadly accepted bond angle guideline. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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Open AccessReview
Biocrystals in Plants: A Short Review on Biomineralization Processes and the Role of Phototropins into the Uptake of Calcium
Crystals 2020, 10(7), 591; https://doi.org/10.3390/cryst10070591 - 09 Jul 2020
Viewed by 208
Abstract
The biomineralization process is a mechanism inherent to all organisms of the Earth. Throughout the decades, diverse works have reported that the origin of life is tied to crystals, specifically to biominerals of silica that catalyzed RNA, and had some influence in the [...] Read more.
The biomineralization process is a mechanism inherent to all organisms of the Earth. Throughout the decades, diverse works have reported that the origin of life is tied to crystals, specifically to biominerals of silica that catalyzed RNA, and had some influence in the homochirality. Although the mechanism by which crystals surfaces (minerals) gave origin to life has not yet been proven, the truth is that, up to the present, biominerals are being synthetized by the organisms of different kingdoms in two basic ways: biologically induced and biologically controlled biomineralization. Paradoxically, this fact makes a fundamental difference between inorganic materials and those formed by living organisms, as the latter are associated with macromolecules that are bound to the mineral phase. Conserving growth and formation of these biogenic organic crystals inside cells is a fascinating subject that has been studied mainly in some of the kingdoms, like Monera (bacteria), Fungi (yeasts), and Animalia (Homo sapiens). Notwithstanding in the Plantae kingdom, the formation, conservation, and functions of crystals has not yet been completely elucidated and described, which is of particular relevance because life on Earth, as we know it, would not be possible without plants. The aim of the present work is to revise the different crystals of calcium oxalate synthetized inside the cells of plants, as well as to identify the mechanism of their formation and their possible functions in plants. The last part is related to the existence of certain proteins called phototropins, which not only work as the blue-light sensors, but they also play an important role on the accumulation of calcium in vacuoles. This new trend is shortly reviewed to explain the characteristics and their plausible role in the calcium uptake along with the biomineralization processes. Full article
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Open AccessArticle
Extraordinary Response of H-Charged and H-Free Coherent Grain Boundaries in Nickel to Multiaxial Loading
Crystals 2020, 10(7), 590; https://doi.org/10.3390/cryst10070590 - 08 Jul 2020
Viewed by 191
Abstract
The cohesive strength of 3, 5, and 11 grain boundaries (GBs) in clean and hydrogen-segregated fcc nickel was systematically studied as a function of the superimposed transverse biaxial stresses using ab initio methods. The obtained results for H-free GBs revealed a quite different [...] Read more.
The cohesive strength of 3, 5, and 11 grain boundaries (GBs) in clean and hydrogen-segregated fcc nickel was systematically studied as a function of the superimposed transverse biaxial stresses using ab initio methods. The obtained results for H-free GBs revealed a quite different response of the coherent twinning boundary 3 to the applied transverse stresses in comparison to the other GB types. While the cohesive strength of 5 and 11 GBs increased with increasing level of tensile transverse stresses, the strength of 3 GB remained constant for any applied levels of transverse stresses. In the case of GBs with segregated hydrogen, the cohesive strength of 3 was distinctly reduced for all levels of transverse stresses, while the strength reduction of 5 and 11 GBs was significant only for a nearly isotropic (hydrostatic) triaxial loading. This extraordinary response explains a high susceptibility of 3 GBs to crack initiation, as recently reported in an experimental study. Moreover, a highly triaxial stress at the fronts of microcracks initiated at 3 boundaries caused a strength reduction of adjacent high-energy grain boundaries which thus became preferential sites for further crack propagation. Full article
(This article belongs to the Special Issue Crystal Plasticity at Micro- and Nano-scale Dimensions)
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Open AccessReview
Synthesis of Metal Nanoparticles by Microorganisms
Crystals 2020, 10(7), 589; https://doi.org/10.3390/cryst10070589 - 08 Jul 2020
Viewed by 171
Abstract
Metal nanoparticles (NPs), with sizes ranging from 1–100 nm, are of great scientific interest because their functions and features differ greatly from those of bulk metal. Chemical or physical methods are used to synthesize commercial quantities of NPs, and green, energy-efficient approaches generating [...] Read more.
Metal nanoparticles (NPs), with sizes ranging from 1–100 nm, are of great scientific interest because their functions and features differ greatly from those of bulk metal. Chemical or physical methods are used to synthesize commercial quantities of NPs, and green, energy-efficient approaches generating byproducts of low toxicity are desirable to minimize the environmental impact of the industrial methods. Some microorganisms synthesize metal NPs for detoxification and metabolic reasons at room temperature and pressure in aqueous solution. Metal NPs have been prepared via green methods by incubating microorganisms or cell-free extracts of microorganisms with dissolved metal ions for hours or days. Metal NPs are analyzed using various techniques, such as ultraviolet-visible spectroscopy, electron microscopy, X-ray diffraction, electron diffraction, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Numerous publications have focused on microorganisms that synthesize various metal NPs. For example, Ag, Au, CdS, CdSe, Cu, CuO, Gd2O3, Fe3O4, PbS, Pd, Sb2O3, TiO2, and ZrO2 NPs have been reported. Herein, we review the synthesis of metal NPs by microorganisms. Although the molecular mechanisms of their synthesis have been investigated to some extent, experimental evidence for the mechanisms is limited. Understanding the mechanisms is crucial for industrial-scale development of microorganism-synthesized metal NPs. Full article
(This article belongs to the Special Issue Biominerals: Formation, Function, Properties)
Open AccessArticle
EM-detwin: A Program for Resolving Indexing Ambiguity in Serial Crystallography Using the Expectation-Maximization Algorithm
Crystals 2020, 10(7), 588; https://doi.org/10.3390/cryst10070588 - 08 Jul 2020
Viewed by 143
Abstract
Serial crystallography (SX), first used as an application of X-ray free-electron lasers (XFELs), is becoming a useful method to determine atomic-resolution structures of proteins from micrometer-sized crystals with bright X-ray sources. Because of unknown orientations of crystals in SX, indexing ambiguity issue arises [...] Read more.
Serial crystallography (SX), first used as an application of X-ray free-electron lasers (XFELs), is becoming a useful method to determine atomic-resolution structures of proteins from micrometer-sized crystals with bright X-ray sources. Because of unknown orientations of crystals in SX, indexing ambiguity issue arises when the symmetry of Bravais lattice is higher than the space group symmetry, making some diffraction signals wrongly merged to the total intensity in twinned orientations. In this research, we developed a program within the CrystFEL framework, the EM-detwin, to resolve this indexing ambiguity problem based on the expectation-maximization algorithm. Testing results on the performance of the EM-detwin have demonstrated its usefulness in correctly indexing diffraction data as a valuable tool for SX data analysis. Full article
(This article belongs to the Special Issue Crystallography at X-ray Free-Electron Lasers (XFELs))
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Open AccessArticle
Design, Synthesis, Crystal Structure, and Fungicidal Activity of Two Fenclorim Derivatives
Crystals 2020, 10(7), 587; https://doi.org/10.3390/cryst10070587 - 07 Jul 2020
Viewed by 214
Abstract
Two fenclorim derivatives (compounds 6 and 7) were synthesized by linking active sub-structures using fenclorim as the lead compound. The chemical structures of the two compounds were confirmed by NMR spectroscopy, high resolution mass spectrometry, and X-ray diffraction analysis. Their fungicidal activity [...] Read more.
Two fenclorim derivatives (compounds 6 and 7) were synthesized by linking active sub-structures using fenclorim as the lead compound. The chemical structures of the two compounds were confirmed by NMR spectroscopy, high resolution mass spectrometry, and X-ray diffraction analysis. Their fungicidal activity against six plant fungal strains was tested. Compounds 6 and 7 both crystallized in the monoclinic system, with a P21/c space group (a = 8.4842(6) Å, b = 24.457(2) Å, c = 8.9940(6) Å, V = 1855.0(2) Å3, Z = 4) and Cc space group (a = 10.2347(7) Å, b = 18.3224(10) Å, c = 7.2447(4) Å, V = 1357.50(14) Å3, Z = 4), respectively. The crystal structure of compound 6 was stabilized by C–H···N and C–H···O hydrogen bonding interactions and N–H···N hydrogen bonds linked the neighboring molecules of compound 7 to form a three-dimensional framework. Compound 6 displayed the most excellent activity, which is much better than that of pyrimethanil against Botrytis cinerea in vivo. Additionally, compound 6 exhibited greater in vitro activity against Pseudoperonospora cubensis compared to that of pyrimethanil. Moreover, compound 7 exhibited strong fungicidal activity against Erysiphe cichoracearum at 50 mg/L in vitro, while pyrimethanil did not. Compounds 6 and 7 could be used as new pyrimidine fungicides in the future. Full article
(This article belongs to the Special Issue Pharmaceutical Crystals (Volume II))
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Open AccessCommunication
Modelling Propagating Bloch Waves in Magnetoelectroelastic Phononic Structures with Kagomé Lattice Using the Improved Plane Wave Expansion
Crystals 2020, 10(7), 586; https://doi.org/10.3390/cryst10070586 - 07 Jul 2020
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Abstract
We studied the dispersion diagram of a 2D magnetoelectroelastic phononic crystal (MPnC) with Kagomé lattice. The MPnC is composed of BaTiO3–CoFe2O4 circular scatterers embedded in a polymeric matrix. The improved plane wave expansion (IPWE) approach was used to calculate the dispersion diagram (only [...] Read more.
We studied the dispersion diagram of a 2D magnetoelectroelastic phononic crystal (MPnC) with Kagomé lattice. The MPnC is composed of BaTiO3–CoFe2O4 circular scatterers embedded in a polymeric matrix. The improved plane wave expansion (IPWE) approach was used to calculate the dispersion diagram (only propagating modes) of the MPnC considering the classical elasticity theory, solid with transverse isotropy and wave propagation in the xy plane. Complete Bragg-type forbidden bands were observed for XY and Z modes. The piezoelectric and the piezomagnetic effects significantly influenced the forbidden band widths and localizations. This investigation can be valuable for elastic wave manipulation using smart phononic crystals with piezoelectric and piezomagnetic effects. Full article
(This article belongs to the Special Issue Metamaterials)
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Open AccessPerspective
A Perspective on Molecular Structure and Bonding-Breaking in Radiation Damage in Serial Femtosecond Crystallography
Crystals 2020, 10(7), 585; https://doi.org/10.3390/cryst10070585 - 06 Jul 2020
Viewed by 286
Abstract
X-ray free-electron lasers (XFELs) have a unique capability for time-resolved studies of protein dynamics and conformational changes on femto- and pico-second time scales. The extreme intensity of X-ray pulses can potentially cause significant modifications to the sample structure during exposure. Successful time-resolved XFEL [...] Read more.
X-ray free-electron lasers (XFELs) have a unique capability for time-resolved studies of protein dynamics and conformational changes on femto- and pico-second time scales. The extreme intensity of X-ray pulses can potentially cause significant modifications to the sample structure during exposure. Successful time-resolved XFEL crystallography depends on the unambiguous interpretation of the protein dynamics of interest from the effects of radiation damage. Proteins containing relatively heavy elements, such as sulfur or metals, have a higher risk for radiation damage. In metaloenzymes, for example, the dynamics of interest usually occur at the metal centers, which are also hotspots for damage due to the higher atomic number of the elements they contain. An ongoing challenge with such local damage is to understand the residual bonding in these locally ionized systems and bond-breaking dynamics. Here, we present a perspective on radiation damage in XFEL experiments with a particular focus on the impacts for time-resolved protein crystallography. We discuss recent experimental and modelling results of bond-breaking and ion motion at disulfide bonding sites in protein crystals. Full article
(This article belongs to the Special Issue Time Resolved Crystallography)
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Open AccessArticle
Growth and Scintillation Properties of Directionally Solidified Ce:LaBr3/AEBr2 (AE = Mg, Ca, Sr, Ba) Eutectic System
Crystals 2020, 10(7), 584; https://doi.org/10.3390/cryst10070584 - 06 Jul 2020
Viewed by 235
Abstract
Ce-doped LaBr3/AEBr2 (AE = Mg, Ca, Sr, Ba) eutectics were grown using the Bridgman–Stockbarger (BS) method in quartz ampoules. The eutectics (AE = Mg and Ca) showed optical transparency like optical fiber bundles. A grown Ce-doped LaBr3/MgBr2 [...] Read more.
Ce-doped LaBr3/AEBr2 (AE = Mg, Ca, Sr, Ba) eutectics were grown using the Bridgman–Stockbarger (BS) method in quartz ampoules. The eutectics (AE = Mg and Ca) showed optical transparency like optical fiber bundles. A grown Ce-doped LaBr3/MgBr2 eutectic shows a 355 nm emission ascribed to Ce3+ 4f-5d transition under X-ray excitation. The smaller the ionic size of AE, the higher the light yield of the sample was. The light yield of Ce:LaBr3/MgBr2 was 34,300 photon/MeV, which is higher than Ce:LYSO standard. Scintillation decay time under 662 keV gamma-ray excitation was 18.8 ns. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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Open AccessArticle
In Situ Imaging of Domain Structure Evolution in LaBGeO5 Single Crystals
Crystals 2020, 10(7), 583; https://doi.org/10.3390/cryst10070583 - 06 Jul 2020
Viewed by 182
Abstract
LaBGeO5 (LBGO) crystals are unique ferroelectric materials for manufacturing highly efficient UV laser sources based on frequency conversion. This is due to their low cut-off wavelength, high nonlinear-optical coefficients, and non-hygroscopicity. Periodical poling requires a deep study of domain kinetics in these [...] Read more.
LaBGeO5 (LBGO) crystals are unique ferroelectric materials for manufacturing highly efficient UV laser sources based on frequency conversion. This is due to their low cut-off wavelength, high nonlinear-optical coefficients, and non-hygroscopicity. Periodical poling requires a deep study of domain kinetics in these crystals. Domain imaging by Cherenkov second harmonic generation microscopy was used to reveal the main processes of domain structure evolution: (1) growth and merging of isolated domains, (2) growth of stripe domains formed on the artificial linear surface defects, and (3) domain shrinkage. In a low field, growth of triangular domains and fast shape recovery after merging were observed, while in a high field, the circular domains grew independently after merging. The revealed essential wall motion anisotropy decreased with the field. The anisotropy led to significant shape transformations during domain shrinkage in low field. The formation of short-lived triangular domains rotated by 180 degrees with respect to the growing isolated domains was observed. The obtained results were explained within the kinetic approach to domain structure evolution based on the analogy between the growth of crystals and ferroelectric domains, taking into account the gradual transition from determined nucleation in low field to the stochastic one in high field. Full article
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Open AccessArticle
Properties of N-Type GaN Thin Film with Si-Ti Codoping on a Glass Substrate
Crystals 2020, 10(7), 582; https://doi.org/10.3390/cryst10070582 - 05 Jul 2020
Viewed by 302
Abstract
In this study, n-type gallium nitride (GaN) films were fabricated by a silicon–titanium (Si-Ti) codoping sputtering technique with a zinc oxide (ZnO) buffer layer on amorphous glass substrates with different post-growth annealing temperatures for optimizing the GaN crystal quality. Si-Ti-codoped n-type GaN films [...] Read more.
In this study, n-type gallium nitride (GaN) films were fabricated by a silicon–titanium (Si-Ti) codoping sputtering technique with a zinc oxide (ZnO) buffer layer on amorphous glass substrates with different post-growth annealing temperatures for optimizing the GaN crystal quality. Si-Ti-codoped n-type GaN films that were thermally annealed at 400 °C had a low thin-film resistivity of 2.6 × 10−1 Ω-cm and a high electron concentration of 6.65 × 1019 cm−3, as determined through Hall measurement. X-ray diffraction (XRD) results revealed a high (002) XRD intensity with a narrow spectral line and a full width at half maximum (FWHM) value that indicated the superior crystal growth of a hexagonal structure of the GaN thin films. In addition, photoluminescence measurement results demonstrated a near-band-edge emission at 365 nm, indicating the crystal growth of GaN thin films on glass substrates. The Burstein–Moss effect was observed in the Tauc plot results, indicating that the Fermi level inside the conduction band moves upward and thus improves the n-type properties of the GaN thin film. X-ray photoelectron spectroscopy measurement results revealed that all atoms doped into the GaN film are present and that both Si and Ti atoms bond with N atoms. Full article
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Open AccessArticle
Principal Component Analysis (PCA) for Powder Diffraction Data: Towards Unblinded Applications
Crystals 2020, 10(7), 581; https://doi.org/10.3390/cryst10070581 - 05 Jul 2020
Viewed by 227
Abstract
We analyze the application of Principal Component Analysis (PCA) for untangling the main contributions to changing diffracted intensities upon variation of site occupancy and lattice dimensions induced by external stimuli. The information content of the PCA output consists of certain functions of Bragg [...] Read more.
We analyze the application of Principal Component Analysis (PCA) for untangling the main contributions to changing diffracted intensities upon variation of site occupancy and lattice dimensions induced by external stimuli. The information content of the PCA output consists of certain functions of Bragg angles (loadings) and their evolution characteristics that depend on external variables like pressure or temperature (scores). The physical meaning of the PCA output is to date not well understood. Therefore, in this paper, the intensity contributions are first derived analytically, then compared with the PCA components for model data; finally PCA is applied for the real data on isothermal gas uptake by nanoporous framework γ –Mg(BH 4 ) 2 . We show that, in close agreement with previous analysis of modulation diffraction, the variation of intensity of Bragg lines and the displacements of their positions results in a series of PCA components. Every PCA extracted component may be a mixture of terms carrying information on the average structure, active sub-structure, and their cross-term. The rotational ambiguities, that are an inherently part of PCA extraction, are at the origin of the mixing. For the experimental case considered in the paper, the extraction of the physically meaningful loadings and scores can only be achieved with a rotational correction. Finally, practical recommendations for non-blind applications, i.e., what boundary conditions to apply for the the rotational correction, of PCA for diffraction data are given. Full article
(This article belongs to the Special Issue Multivariate Analysis Applications to Crystallography)
Open AccessReview
The Resolution in X-ray Crystallography and Single-Particle Cryogenic Electron Microscopy
Crystals 2020, 10(7), 580; https://doi.org/10.3390/cryst10070580 - 05 Jul 2020
Viewed by 278
Abstract
X-ray crystallography and single-particle analysis cryogenic electron microscopy are essential techniques for uncovering the three-dimensional structures of biological macromolecules. Both techniques rely on the Fourier transform to calculate experimental maps. However, one of the crucial parameters, resolution, is rather broadly defined. Here, the [...] Read more.
X-ray crystallography and single-particle analysis cryogenic electron microscopy are essential techniques for uncovering the three-dimensional structures of biological macromolecules. Both techniques rely on the Fourier transform to calculate experimental maps. However, one of the crucial parameters, resolution, is rather broadly defined. Here, the methods to determine the resolution in X-ray crystallography and single-particle analysis are summarized. In X-ray crystallography, it is becoming increasingly more common to include reflections discarded previously by traditionally used standards, allowing for the inclusion of incomplete and anisotropic reflections into the refinement process. In general, the resolution is the smallest lattice spacing given by Bragg’s law for a particular set of X-ray diffraction intensities; however, typically the resolution is truncated by the user during the data processing based on certain parameters and later it is used during refinement. However, at which resolution to perform such a truncation is not always clear and this makes it very confusing for the novices entering the structural biology field. Furthermore, it is argued that the effective resolution should be also reported as it is a more descriptive measure accounting for anisotropy and incompleteness of the data. In single particle cryo-EM, the situation is not much better, as multiple ways exist to determine the resolution, such as Fourier shell correlation, spectral signal-to-noise ratio and the Fourier neighbor correlation. The most widely accepted is the Fourier shell correlation using a threshold of 0.143 to define the resolution (so-called “gold-standard”), although it is still debated whether this is the correct threshold. Besides, the resolution obtained from the Fourier shell correlation is an estimate of varying resolution across the density map. In reality, the interpretability of the map is more important than the numerical value of the resolution. Full article
Open AccessArticle
A Self-Assembled Hetero-Bimetallic [Ni(II)-Sm(III)] Coordination Polymer Constructed from a Salamo-Like Ligand and 4,4′-Bipyridine: Synthesis, Structural Characterization, and Properties
Crystals 2020, 10(7), 579; https://doi.org/10.3390/cryst10070579 - 04 Jul 2020
Viewed by 273
Abstract
An unusual self-assembled hetero-bimetallic [Ni(II)-Sm(III)] coordination polymer, [Ni(L)Sm(NO3)3(4,4′-bipy)]n, is prepared through a hexadentate chelating ligand 2,2′-[1,2-ethylenedioxybis(nitrilomethylidyne)]diphenol (H2L). The Ni(II)-Sm(III) coordination polymer is validated through elemental analyses, Fourier-transform infrared and UV-Visible spectroscopies, and X-ray single-crystal diffraction. [...] Read more.
An unusual self-assembled hetero-bimetallic [Ni(II)-Sm(III)] coordination polymer, [Ni(L)Sm(NO3)3(4,4′-bipy)]n, is prepared through a hexadentate chelating ligand 2,2′-[1,2-ethylenedioxybis(nitrilomethylidyne)]diphenol (H2L). The Ni(II)-Sm(III) coordination polymer is validated through elemental analyses, Fourier-transform infrared and UV-Visible spectroscopies, and X-ray single-crystal diffraction. The Ni(II) atom forms a twisted six-coordinated octahedron, and the Sm(III) atom is ten-coordinated, adopting a twisted bicapped square antiprism. An infinite three-dimensional-layer supramolecular structure is obtained through extensive π···π stacking and intermolecular hydrogen bonding interactions. The polymer has a good antibacterial effect against Staphylococcus aureus. Full article
(This article belongs to the Special Issue Coordination Polymers: Structure, Bonding and Applications)
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Open AccessArticle
Partial and Total Substitution of Zn by Mg in the Cu2ZnSnS4 Structure
Crystals 2020, 10(7), 578; https://doi.org/10.3390/cryst10070578 - 04 Jul 2020
Viewed by 282
Abstract
Cu 2 ZnSnS 4 (CZTS) is a quaternary semiconductor that has emerged as a promising component in solar absorber materials due to its excellent optical properties such as band-gap energy of ca. 1.5 eV and significant absorption coefficient in the order of 10 [...] Read more.
Cu 2 ZnSnS 4 (CZTS) is a quaternary semiconductor that has emerged as a promising component in solar absorber materials due to its excellent optical properties such as band-gap energy of ca. 1.5 eV and significant absorption coefficient in the order of 10 4 cm 1 . Nevertheless, the energy conversion efficiency of CZTS-based devices has not reached the theoretical limits yet, possibly due to the existence of antisite defects (such as Cu Zn or Zn Cu ) and secondary phases. Based on electronic similarities with Zn, Mg has been proposed for Zn substitution in the CZTS structure in the design of alternative semiconductors for thin-film solar cell applications. This work aims to study the properties of the CZTS having Mg incorporated in the structure replacing Zn, with the following stoichiometry: x = 0, 0.25, 0.5, 0.75, and 1 in the formula Cu 2 Zn 1 x Mg x SnS 4 (CZ-MTS). The semiconductor was prepared by the hot injection method, using oleylamine (OLA) as both surfactant and solvent. The presence and concentration of incorporated Mg allowed the fine-tuning of the CZ-MTS semiconductor’s structural and optical properties. Furthermore, it was observed that the inclusion of Mg in the CZTS structure leads to a better embodiment ratio of the Zn during the synthesis, thus reducing the excess of starting precursors. In summary, CZ-MTS is a promising candidate to fabricate high efficient and cost-effective thin-film solar cells made of earth-abundant elements. Full article
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