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Crystals, Volume 10, Issue 11 (November 2020) – 114 articles

Cover Story (view full-size image): Keldyshite-related compounds and materials attract increasing interest because of their outstanding ion-exchange properties and are considered advanced materials, analogs of zeolites. The keldyshite group combines keldyshite Na3H[Zr2(Si2O7)2] and parakeldyshite Na2[Zr(Si2O7)]; synthetic compound Na2[Zr(Si2O7)]∙H2O chemically related to this group. Their crystal structures contain microporous heteropolyhedral frameworks formed by Si2O7-diorthogroups and ZrO6-octahedra with wide channels filled by sodium cations and water molecules. The microporous heteropolyhedral frameworks of all compounds have 2D systems of wide channels suitable for the Na+-ion migration. The crystal structure of keldyshite can be derived from parakeldyshite structure by Na+ + O2‒ ↔ OH‒ + □ substitution, widespread in the post-crystallization process of hyperagpaitic rocks. View this paper.
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Article
Chiral Conducting Me-EDT-TTF and Et-EDT-TTF-Based Radical Cation Salts with the Perchlorate Anion
Crystals 2020, 10(11), 1069; https://doi.org/10.3390/cryst10111069 - 23 Nov 2020
Cited by 5 | Viewed by 1172
Abstract
Introduction of chirality in the field of molecular conductors has received increasing interest in recent years in the frame of modulation of the crystal packing, and hence conducting properties, with the number of stereogenic centers and absolute configuration, e.g., racemic or enantiopure forms. [...] Read more.
Introduction of chirality in the field of molecular conductors has received increasing interest in recent years in the frame of modulation of the crystal packing, and hence conducting properties, with the number of stereogenic centers and absolute configuration, e.g., racemic or enantiopure forms. Here, we describe the preparation by electrocrystallization of chiral radical cation salts, based on the donors methyl-ethylenedithio-tetrathiafulvalene (Me-EDT-TTF) 1 and ethyl-ethylenedithio-tetrathiafulvalene (Et-EDT-TTF) 2 containing one stereogenic center, with the perchlorate anion. Donor 1 provided the series of crystalline materials [(rac)-1]ClO4, [(S)-1]2ClO4 and [(R)-1]2ClO4, while for donor 2 only the 1:1 salts [(rac)-2]ClO4 and [(R)-2]ClO4 could be prepared as suitable single crystals for X-ray analysis. The enantiopure salts of 1 show β-type packing and metallic conductivity in the high temperature regime, with room temperature conductivity values of 5–10 S cm−1, whereas compound [(rac)-2]ClO4 is a very poor semiconductor. Tight-binding extended Hückel band structure calculations support the metallic conductivity of the enantiopure salts of 1 and suggest that small structural changes, possibly induced by thermal contraction or pressure, could lead to a pseudo-elliptic closed Fermi surface, typical for a 2D metal. Full article
(This article belongs to the Special Issue Organic Conductors)
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Article
Microstructural Characterization and Corrosion-Resistance Behavior of Dual-Phase Steels Compared to Conventional Rebar
Crystals 2020, 10(11), 1068; https://doi.org/10.3390/cryst10111068 - 23 Nov 2020
Cited by 9 | Viewed by 817
Abstract
Dual-phase (DP) steels consist of a ferritic matrix dispersed with some percentage of martensite, which gives the material a good combination of strength and ductility, along with the capacity to absorb energy and enhanced corrosion protection properties. The purpose of this work was [...] Read more.
Dual-phase (DP) steels consist of a ferritic matrix dispersed with some percentage of martensite, which gives the material a good combination of strength and ductility, along with the capacity to absorb energy and enhanced corrosion protection properties. The purpose of this work was to study the microstructural and corrosion behavior (mainly pitting and galvanic corrosion) of DP steel compared with that of conventional rebar. To obtain DP steel, low-carbon steels were heat-treated at 950 °C for 1 h and then intercritically annealed at 771 °C for 75 min, followed by quenching in ice-brine water. The corrosion rates of DP steel and standard rebar were then measured in different pore solutions. Macro- and microhardness tests were performed for both steels. It was found that DP steels exhibited a superior corrosion resistance and strength compared to standard rebar. The reported results show that DP steels are a good candidate for concrete reinforcement, especially in aggressive and corrosive environments. Full article
(This article belongs to the Special Issue Microstructural and Mechanical Characterization of Alloys Volume II)
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Editorial
Special Issue “Intermetallic Compound”
Crystals 2020, 10(11), 1067; https://doi.org/10.3390/cryst10111067 - 23 Nov 2020
Cited by 1 | Viewed by 702
Abstract
This Special Issue collects ten articles related to the broadly understood physical properties of intermetallic compounds [...] Full article
(This article belongs to the Special Issue Intermetallic Compound)
Editorial
Deposition and Growth of Functional Nanomaterials by LDW and MAPLE Techniques
Crystals 2020, 10(11), 1066; https://doi.org/10.3390/cryst10111066 - 23 Nov 2020
Viewed by 665
Abstract
Actual societal challenges require a vigorous progress on functional materials with improved functionalities [...] Full article
Article
A Facile and Rapid Fabrication of Multifunctional Color-Tuned Titanium
Crystals 2020, 10(11), 1065; https://doi.org/10.3390/cryst10111065 - 23 Nov 2020
Viewed by 997
Abstract
In this article, a strategy for the fabrication of color-tuned titanium using a torch was developed. The torch was used to manufacture a layer of titanium dioxide on titanium substrates. The reaction time and requirements were reduced compared to the anodization process. Various [...] Read more.
In this article, a strategy for the fabrication of color-tuned titanium using a torch was developed. The torch was used to manufacture a layer of titanium dioxide on titanium substrates. The reaction time and requirements were reduced compared to the anodization process. Various colors appeared depending on the time of torch heating, and this torched-titanium substrate was treated with octadecyltriethoxylsilane (ODTS) to gain superhydrophobic properties for self-cleaning. Scanning Electron Microscope (SEM), Raman spectroscopy, and Atomic Force Microscope (AFM) were used for surface analysis. Besides, the mechanical and ODTS stability of the surface were evaluated through a cross-cut adhesion tape test and water contact angle measurement, proving that the torch is a suitable fabrication process for multifunctional color-tuned titanium. Full article
(This article belongs to the Special Issue TiO2 and Its Nanocomposites)
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Article
Quasi Natural Approach for Crystallization of Zeolites from Different Fly Ashes and Their Application as Adsorbent Media for Malachite Green Removal from Polluted Waters
Crystals 2020, 10(11), 1064; https://doi.org/10.3390/cryst10111064 - 23 Nov 2020
Cited by 4 | Viewed by 822
Abstract
Worldwide disposal of multi-tonnage solid waste from coal-burning thermal power plants (TPPs) creates serious environmental and economic problems, which necessitate the recovery of industrial waste in large quantities and at commercial prices. Fly ashes (FAs) and slag from seven Bulgarian TPPs have been [...] Read more.
Worldwide disposal of multi-tonnage solid waste from coal-burning thermal power plants (TPPs) creates serious environmental and economic problems, which necessitate the recovery of industrial waste in large quantities and at commercial prices. Fly ashes (FAs) and slag from seven Bulgarian TPPs have been successfully converted into valuable zeolite-like composites with various applications, including as adsorbents for capturing CO2 from gases and for removal of contaminants from water. The starting materials generated from different types of coal are characterized by a wide range of SiO2/Al2O3 ratio, heterogeneous structure and a complex chemical composition. The applied synthesis procedure resembles the formation of natural zeolites, as the raw FAs undergo long-term self-crystallization in an alkaline aqueous solution at ambient temperature. The phase and chemical composition, morphology and N2 adsorption of the final zeolite products were studied by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), X-Ray Diffraction (XRD) and Brunauer–Emmett–Teller (BET) analyses. The growth of faujasite (FAU) crystals as the main zeolite phase was established in all samples after 7 and 14 months of alkaline treatment. Phillipsite (PHI) crystals were also observed in several samples as an accompanying phase. The final products possess specific surface area over 400 m2/g. The relationships between the surface properties of the investigated samples and the characteristics of the raw FAs were discussed. All of the obtained zeolite-like composites were able to remove the highly toxic dye (malachite green, MG) from water solutions with efficiency over 96%. The experimental data were fitted with high correlation to the second-order kinetics. Full article
(This article belongs to the Special Issue Zeolites)
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Article
Experimental and Modeling Analysis of Holey Graphene Electrodes for High-Power-Density Li-Ion Batteries
Crystals 2020, 10(11), 1063; https://doi.org/10.3390/cryst10111063 - 22 Nov 2020
Cited by 4 | Viewed by 1021
Abstract
The performances of lithium-ion batteries (LIBs) using holey graphene (HGNS) as the anode material are compared with those using non-holey graphene (GNS). The effects of graphene holes on ion transport are analyzed with a combined experiment/modeling approach involving molecular dynamics (MD) simulations. The [...] Read more.
The performances of lithium-ion batteries (LIBs) using holey graphene (HGNS) as the anode material are compared with those using non-holey graphene (GNS). The effects of graphene holes on ion transport are analyzed with a combined experiment/modeling approach involving molecular dynamics (MD) simulations. The large aspect ratio of GNS leads to long transport paths for Li ions, and hence a poor rate capability. We demonstrate by both experiments and simulations that the holey structure can effectively improve the rate capability of LIBs by providing shortcuts for Li ion diffusion through the holes in fast charge/discharge processes. The HGNS anode exhibits a high specific capacity of 745 mAh/g at 0.1 A/g (after 80 cycles) and 141 mAh/g at a large current density of 10 A/g, which are higher than the capacity values of the GNS counterpart by 75% and 130%, respectively. MD simulations also reveal the difference in lithium ion transport between GNS and HGNS anodes. The calculations indicate that the HGNS system has a higher diffusion coefficient for lithium ions than the GNS system. In addition, it shows that the holey structure can improve the uniformity and quality of the solid electrolyte interphase (SEI) layer, which is important for Li ion conduction across this layer to access the electrode surface. Moreover, quantum chemistry (QC) computations show that ethylene carbonate (EC), a cyclic carbonate electrolyte with five-membered-ring molecules, has the lowest electron binding energy of 1.32 eV and is the most favorable for lithium-ion transport through the SEI layer. A holey structure facilitates uniform dispersion of EC on graphene sheets and thus enhances the Li ion transport kinetics. Full article
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Article
Crystal Chemistry of Alkali–Aluminum–Iron Sulfates from the Burnt Mine Dumps of the Chelyabinsk Coal Basin, South Urals, Russia
Crystals 2020, 10(11), 1062; https://doi.org/10.3390/cryst10111062 - 22 Nov 2020
Cited by 1 | Viewed by 1047
Abstract
Technogenic steklite, KAl(SO4)2, and unnamed mineral phase (K,Na)3Na3(Fe,Al)2(SO4)6 from burnt dumps of the Chelyabinsk Coal Basin have been investigated by single-crystal X-ray diffraction and electron microprobe analysis. Steklite is trigonal, [...] Read more.
Technogenic steklite, KAl(SO4)2, and unnamed mineral phase (K,Na)3Na3(Fe,Al)2(SO4)6 from burnt dumps of the Chelyabinsk Coal Basin have been investigated by single-crystal X-ray diffraction and electron microprobe analysis. Steklite is trigonal, space group P3¯, a = 4.7277(3), c = 7.9871(5) Å, V = 154.60(2) Å3. The crystal structure was refined to R1 = 0.026 (wR2 = 0.068). It is based upon the [Al(SO4)2] layers formed by corner sharing of SO4 tetrahedra and AlO6 polyhedra. The anionic [Al(SO4)2] layers are parallel to the (001) plane and linked via interlayer K+ ions. The regular octahedral coordination of Al is observed that distinguishes technogenic steklite from that found in Tolbachik fumaroles. The (K,Na)3Na3(Fe,Al)2(SO4)6 phase is trigonal, space group R3¯, a = 13.932(2), c = 17.992(2) Å, V = 3024.4(7) Å3, R1 = 0.073 (wR2 = 0.108). The crystal structure is based upon the anionic chains [(Fe,Al)(SO4)3]3− running parallel to the c axis and interconnected via K+ and Na+ ions. There are no known minerals or synthetic compounds isotypic to (K,Na)3Na3(Fe,Al)2(SO4)6, due to the presence of separate K and Na sites in its structure. Full article
(This article belongs to the Special Issue Crystal Chemistry and Properties of Minerals)
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Article
Dissolution Behavior of Al2O3 Inclusions in CaO-Al2O3 Based Slag Representing Aluminothermic Reduction Slag
Crystals 2020, 10(11), 1061; https://doi.org/10.3390/cryst10111061 - 22 Nov 2020
Cited by 2 | Viewed by 897
Abstract
In the preparation of CuCr alloy using the self-propagating high-temperature synthesis (SHS)-metallurgy method, the dissolution of alumina in molten slag has an important influence in two key steps: aluminum thermal reduction and slag refining. In the present work, the dissolution behavior of Al [...] Read more.
In the preparation of CuCr alloy using the self-propagating high-temperature synthesis (SHS)-metallurgy method, the dissolution of alumina in molten slag has an important influence in two key steps: aluminum thermal reduction and slag refining. In the present work, the dissolution behavior of Al2O3 into molten SHS-metallurgical slags was investigated by employing the rotating cylinder method and static dissolution method. It is concluded that the increase of MgO, CaF2, CaO, and Na3AlF6 contents can increase the dissolution rate of alumina in SHS-metallurgical slag, and the order of influence is from strong to weak. Both temperature and rotating speed can increase the dissolution rate, and the rate-limiting step is the diffusion of alumina in the boundary layer, with the solid alumina first reacting with lime to form two intermediate phases, CaO·2Al2O3 and CaO·6Al2O3, and finally dissolving into the slag in the form of an aluminum polymer. Full article
(This article belongs to the Special Issue Metallurgical Slag)
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Article
Single Crystal Heat Capacity Measurement of Charge Glass Compound θ-(BEDT-TTF)2CsZn(SCN)4 Performed under Current and Voltage Application
Crystals 2020, 10(11), 1060; https://doi.org/10.3390/cryst10111060 - 21 Nov 2020
Cited by 1 | Viewed by 923
Abstract
Heat capacity measurements of θ-(BEDT-TTF)2CsZn(SCN)4 in its non-equilibrium electronic states induced by applying electric currents and voltages were performed by a modified relaxation calorimetry technique. We developed a single crystal heat capacity measurements system by which the Joule heating produced [...] Read more.
Heat capacity measurements of θ-(BEDT-TTF)2CsZn(SCN)4 in its non-equilibrium electronic states induced by applying electric currents and voltages were performed by a modified relaxation calorimetry technique. We developed a single crystal heat capacity measurements system by which the Joule heating produced in samples by external currents and voltages can be balanced with the cooling power to make a non-equilibrium steady state. Although temperature versus time profiles in the relaxation process in calorimetry can be obtained as exponential curves as in the usual relaxation technique, we found that the change of resistivity that occurs during the heating and relaxation process should be taken into account in analyzing the data. By correcting this factor in the analyses, we succeeded in evaluating absolute values of Cp(I) and Cp(V) in these non-equilibrium states. The experiments up to 150 μA and the constant voltage of 20 mV do not induce visible change in the structure of the Boson peak in CpT−3 vs. T suggestive of the glassy ground state of phonons. Although the suppression of the short-range fluctuations of the charge density has been reported, it does not seriously affect the glassy phonons in this current range. Full article
(This article belongs to the Special Issue Organic Conductors)
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Article
TCAD Simulation Study of ESD Behavior of InGaAs/InP Heterojunction Tunnel FETs
Crystals 2020, 10(11), 1059; https://doi.org/10.3390/cryst10111059 - 21 Nov 2020
Cited by 3 | Viewed by 901
Abstract
For the first time, we investigated the electrostatic discharge (ESD) behavior of an InGaAs/InP heterojunction tunneling field effect transistor (HTFET). The device structure in this study has a high on-state current without extra process steps. Under the positive transmission line pulse (TLP) simulation, [...] Read more.
For the first time, we investigated the electrostatic discharge (ESD) behavior of an InGaAs/InP heterojunction tunneling field effect transistor (HTFET). The device structure in this study has a high on-state current without extra process steps. Under the positive transmission line pulse (TLP) simulation, the band-to-band tunneling (BTBT) current acts as an important initial current to accelerate the occurrence of impact ionization and the device is turned on quickly. Under the negative transmission line pulse (TLP) simulation, the operating principle of the HTFET is the same as for a poly-bounded diode. The ESD robustness of the device under TLP simulation are evaluated, and the impact factors, with regard to ESD robustness and failure mode, are discussed. Finally, the device behavior under very fast transmission line pulse (VFTLP) simulations with different rise times and pulse widths is also investigated. The results show that this device may be used for the ESD protection of next-generation III–V technology. Full article
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Communication
Impact of the Co/Ni-Ratio on Microstructure, Thermophysical Properties and Creep Performance of Multi-Component γ′-Strengthened Superalloys
Crystals 2020, 10(11), 1058; https://doi.org/10.3390/cryst10111058 - 21 Nov 2020
Cited by 5 | Viewed by 1300
Abstract
The Ni content is a crucial factor for the development of γ′-strengthened Co-based superalloys and some studies have systematically addressed its influence on various properties in model superalloys. In this paper, we report for the first time the influence of the Co/Ni ratio [...] Read more.
The Ni content is a crucial factor for the development of γ′-strengthened Co-based superalloys and some studies have systematically addressed its influence on various properties in model superalloys. In this paper, we report for the first time the influence of the Co/Ni ratio in the more advanced nine-component superalloy ERBOCo-1: exchanging Co and Ni in this Co/Ni-based superalloy while keeping the other alloying elements constants has a big influence on a variety of material properties. The elemental segregation after casting is slightly more pronounced in the alloy with higher Ni-content. Microstructural characterization of this alloy termed ERBOCo-1X after heat-treatment reveals that the precipitates are cuboidal in the Co- and spherical in the Ni-rich alloy, indicating a decrease in the γ/γ′ lattice misfit. Analyzing the elemental partitioning behavior by atom probe tomography suggests that the partitioning behavior of W is responsible for that. Furthermore, it is found that even though Ni exhibits the highest overall concentration, the γ matrix phase is still Co-based, because Ni is strongly enriched in the γ′ precipitates. Creep tests at 900 °C reveal that even though the microstructure looks less favorable, the creep resistance of the Ni-rich alloy is slightly superior to the Co-rich variant. Full article
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Review
Halogen Bonds Fabricate 2D Molecular Self-Assembled Nanostructures by Scanning Tunneling Microscopy
Crystals 2020, 10(11), 1057; https://doi.org/10.3390/cryst10111057 - 20 Nov 2020
Viewed by 977
Abstract
Halogen bonds are currently new noncovalent interactions due to their moderate strength and high directionality, which are widely investigated in crystal engineering. The study about supramolecular two-dimensional architectures on solid surfaces fabricated by halogen bonding has been performed recently. Scanning tunneling microscopy (STM) [...] Read more.
Halogen bonds are currently new noncovalent interactions due to their moderate strength and high directionality, which are widely investigated in crystal engineering. The study about supramolecular two-dimensional architectures on solid surfaces fabricated by halogen bonding has been performed recently. Scanning tunneling microscopy (STM) has the advantages of realizing in situ, real-time, and atomic-level characterization. Our group has carried out molecular self-assembly induced by halogen bonds at the liquid–solid interface for about ten years. In this review, we mainly describe the concept and history of halogen bonding and the progress in the self-assembly of halogen-based organic molecules at the liquid/graphite interface in our laboratory. Our focus is mainly on (1) the effect of position, number, and type of halogen substituent on the formation of nanostructures; (2) the competition and cooperation of the halogen bond and the hydrogen bond; (3) solution concentration and solvent effects on the molecular assembly; and (4) a deep understanding of the self-assembled mechanism by density functional theory (DFT) calculations. Full article
(This article belongs to the Special Issue σ- and π-Hole Interactions)
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Article
Probing Lithium-Ion Battery Electrolytes with Laboratory Near-Ambient Pressure XPS
Crystals 2020, 10(11), 1056; https://doi.org/10.3390/cryst10111056 - 20 Nov 2020
Cited by 14 | Viewed by 1426
Abstract
In this article, we present Near Ambient Pressure (NAP)-X-ray Photoelectron Spectroscopy (XPS) results from model and commercial liquid electrolytes for lithium-ion battery production using an automated laboratory NAP-XPS system. The electrolyte solutions were (i) LiPF6 in EC/DMC (LP30) as a [...] Read more.
In this article, we present Near Ambient Pressure (NAP)-X-ray Photoelectron Spectroscopy (XPS) results from model and commercial liquid electrolytes for lithium-ion battery production using an automated laboratory NAP-XPS system. The electrolyte solutions were (i) LiPF6 in EC/DMC (LP30) as a typical commercial battery electrolyte and (ii) LiTFSI in PC as a model electrolyte. We analyzed the LP30 electrolyte solution, first in its vapor and liquid phase to compare individual core-level spectra. In a second step, we immersed a V2O5 crystal as a model cathode material in this LiPF6 solution. Additionally, the LiTFSI electrolyte model system was studied to compare and verify our findings with previous NAP-XPS data. Photoelectron spectra recorded at pressures of 2–10 mbar show significant chemical differences for the different lithium-based electrolytes. We show the enormous potential of laboratory NAP-XPS instruments for investigations of solid-liquid interfaces in electrochemical energy storage systems at elevated pressures and illustrate the simplicity and ease of the used experimental setup (EnviroESCA). Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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Article
Microscopic Observation of π Spin Polarization by d Localized Spin in λ Type BETS Based Organic Superconductors
Crystals 2020, 10(11), 1055; https://doi.org/10.3390/cryst10111055 - 20 Nov 2020
Cited by 1 | Viewed by 722
Abstract
In this study, 77Se NMR measurements were carried out to detect the π spin polarization of the organic BETS (BETS = Bis(ethylenedithio)tetraselenafulvalene) molecule of the field induced superconductor, λ-(BETS)2Fe1−xGaxCl4, which shows a superconducting transition [...] Read more.
In this study, 77Se NMR measurements were carried out to detect the π spin polarization of the organic BETS (BETS = Bis(ethylenedithio)tetraselenafulvalene) molecule of the field induced superconductor, λ-(BETS)2Fe1−xGaxCl4, which shows a superconducting transition at relatively low magnetic field compared to the non-doped λ-(BETS)2FeCl4. From the analysis of the NMR spectrum at low temperature, it was clarified that the exchange interaction between π and 3d spins in the Ga doping system is smaller than that in the Fe salt. It is also clarified that the conduction π spins feel the “averaged” exchange field from the localized 3d spins at the dilute Fe sites. Full article
(This article belongs to the Special Issue Organic Conductors)
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Article
Influence of Al and N Content and Cooling Rate on the Characteristics of Complex MnS Inclusions in AHSS
Crystals 2020, 10(11), 1054; https://doi.org/10.3390/cryst10111054 - 19 Nov 2020
Cited by 3 | Viewed by 770
Abstract
This study focused on the characteristics of complex MnS inclusions in advanced high strength steels. The effect of metal chemistry (Al and N) and the cooling rate of steel were evaluated by analyzing the inclusions present in five laboratory produced steels. The observed [...] Read more.
This study focused on the characteristics of complex MnS inclusions in advanced high strength steels. The effect of metal chemistry (Al and N) and the cooling rate of steel were evaluated by analyzing the inclusions present in five laboratory produced steels. The observed complex MnS inclusions contained Al2O3-MnS, AlN-MnS, and AlON-MnS. An increase in Al content from 0.5% to 6% increased the number of complex MnS inclusions by ~4 times. In comparison, a decrease of ~80% was observed due to the increased N content of steel from <10 ppm to ~50 ppm. MnS precipitation ratio was used to determine the potency of different inclusions forming complex MnS inclusions due to heterogeneous nucleation. It was found that the MnS precipitation ratio of the observed inclusions was related to their misfit with MnS, and it decreased in the order of AlN > AlON > Al2O3. Moreover, it was determined that AlN particles could be easily engulfed at the solidification front relative to Al2O3, which resulted in a higher MnS precipitation ratio for Al2O3 under slow cooling conditions. Full article
(This article belongs to the Special Issue Liquid Steel Alloying Process)
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Article
Numerical Simulation Study on the Front Shape and Thermal Stresses in Growing Multicrystalline Silicon Ingot: Process and Structural Design
Crystals 2020, 10(11), 1053; https://doi.org/10.3390/cryst10111053 - 19 Nov 2020
Cited by 3 | Viewed by 652
Abstract
In this paper, a transient numerical simulation method is used to investigate the effects of the two furnace configurations on the thermal field: the shape of the melt–crystal (M/C) interface and the thermal stress in the growing multicrystalline ingot. First, four different power [...] Read more.
In this paper, a transient numerical simulation method is used to investigate the effects of the two furnace configurations on the thermal field: the shape of the melt–crystal (M/C) interface and the thermal stress in the growing multicrystalline ingot. First, four different power ratios (top power to side power) are investigated, and then three positions (i.e., the vertical, angled, and horizontal positions) of the insulation block are compared with the conventional setup. The power ratio simulation results show that with a descending power ratio, the M/C interface becomes flatter and the thermal stress in the solidified ingot is lower. In our cases, a power ratio of 1:3–1:4 is more feasible for high-quality ingot. The block’s position simulation results indicate that the horizontal block can more effectively reduce the radial temperature gradient, resulting in a flatter M/C interface and lower thermal stress. Full article
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Article
A Coloring Study of the Ga Richest Alkali Gallides: New In- and Hg-Containing Gallides with the RbGa7- and the K3Ga13-Type Structure
Crystals 2020, 10(11), 1052; https://doi.org/10.3390/cryst10111052 - 19 Nov 2020
Cited by 1 | Viewed by 725
Abstract
The Ga-rich gallides of the alkali metals present an interesting, yet still scarcely investigated case of polyanionic cluster compounds with subtle variations in the character of their chemical bonding. In the present work, the Ga richest phases K3Ga13, RbGa [...] Read more.
The Ga-rich gallides of the alkali metals present an interesting, yet still scarcely investigated case of polyanionic cluster compounds with subtle variations in the character of their chemical bonding. In the present work, the Ga richest phases K3Ga13, RbGa7, and CsGa7, which are formally electron-precise Zintl/Wade cluster compounds, are systematically studied with respect to a partial substitution of Ga by In and Hg. The pure hepta-gallides AGa7 (A = Rb/Cs; R3¯m), which were formerly obtained from Ga-rich melts in powder form only, were crystallized from Hg-rich melts. Herein, up to 9.9/13.6% (Rb/Cs) of Ga could be substituted by In, which partly takes the four-bonded [M2] dumbbells connecting layers of Ga-icosahedra. Even though the structures are electron precise, the pseudo band gap does not coincide with the Fermi level. In the most Ga-rich potassium compound K3Ga13 (Cmcm) only 1.2% of In and 2.7% of Hg could be incorporated. Although Rb3Ga13 remains unknown, ternary variants containing 5.2 to 8.2% In could be obtained; this structure is also stabilized by a small Hg-proportion. The likewise closed-shell 3D polyanion consists of all-exo-bonded Ga-icosahedra and closo [Ga11] clusters, which are connected by two tetrahedrally four-bonded Ga and a trigonal-planar three-bonded Ga0. The aspects of the electronic structures and the site-specific Ga↦Hg/In substitution in the polyanion (“coloring”) are discussed for the title compounds and other mixed Ga/In trielides. Full article
(This article belongs to the Special Issue Compounds with Polar Metallic Bonding Volume II)
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Article
Termination Effects in Aluminosilicate and Aluminogermanate Imogolite Nanotubes: A Density Functional Theory Study
Crystals 2020, 10(11), 1051; https://doi.org/10.3390/cryst10111051 - 19 Nov 2020
Cited by 5 | Viewed by 834
Abstract
We investigate termination effects in aluminosilicate (AlSi) and aluminogermanate (AlGe) imogolite nanotubes (NTs) by means of semi-local and range-corrected hybrid Density Functional Theory (DFT) simulations. Following screening and identification of the smallest finite model capable of accommodating full relaxation of the NT terminations [...] Read more.
We investigate termination effects in aluminosilicate (AlSi) and aluminogermanate (AlGe) imogolite nanotubes (NTs) by means of semi-local and range-corrected hybrid Density Functional Theory (DFT) simulations. Following screening and identification of the smallest finite model capable of accommodating full relaxation of the NT terminations around an otherwise geometrically and electrostatically unperturbed core region, we quantify and discuss the effects of physical truncation on the structure, relative energy, electrostatics and electronic properties of differently terminated, finite-size models of the NTs. In addition to composition-dependent changes in the valence (VB) and conduction band (CB) edges and resultant band gap (BG), the DFT simulations uncover longitudinal band bending and separation in the finite AlSi and AlGe models. Depending on the given termination of the NTs, such longitudinal effects manifest in conjunction with the radial band separation typical of fully periodic AlSi and AlGe NTs. The strong composition dependence of the longitudinal and radial band bending in AlSi and AlGe NTs suggests different mechanisms for the generation, relaxation and separation of photo-generated holes in AlSi and AlGe NTs, inviting further research in the untapped potential of imogolite compositional and structural flexibility for photo-catalytic applications. Full article
(This article belongs to the Special Issue Synthesis, Structure, and Properties of Inorganic Nanotubes)
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Editorial
Layered Double Hydroxides
Crystals 2020, 10(11), 1050; https://doi.org/10.3390/cryst10111050 - 19 Nov 2020
Cited by 1 | Viewed by 1006
Abstract
The impact of layered double hydroxides (LDHs) within the multidisciplinary fields of materials sciences, physics, chemistry, and biology is rapidly growing, given their easiness of synthesis, flexibility in composition, tunable biocompatibility and morphology [...] Full article
(This article belongs to the Special Issue Layered Double Hydroxides)
Article
Controlled Size Reduction of Liquid Exfoliated Graphene Micro-Sheets via Tip Sonication
Crystals 2020, 10(11), 1049; https://doi.org/10.3390/cryst10111049 - 18 Nov 2020
Cited by 5 | Viewed by 1096
Abstract
Liquid exfoliation of three-dimensional bulk solids with an inherent layered structure is an effective and scalable method to produce stable re-aggregation colloidal inks of 2D materials that are suitable for solution processing. Shear mixing is a relatively gentle technique that allows exfoliation while [...] Read more.
Liquid exfoliation of three-dimensional bulk solids with an inherent layered structure is an effective and scalable method to produce stable re-aggregation colloidal inks of 2D materials that are suitable for solution processing. Shear mixing is a relatively gentle technique that allows exfoliation while preserving the native lateral size of the 3D precursors, while tip sonication often leads to extensive structural damage, producing 2D sheets where many edge defects are introduced. We present a mixed approach to obtain liquid dispersions of few-layer graphene flakes, wherein the average lateral size of the colloids can be tuned in a controlled way. This strategy relies on the application of defined tip sonication steps on graphene inks previously prepared through the use of a shear mixer, thus starting with already-exfoliated micro-sheets with a limited amount of edge defects. Our approach could represent a valuable method to prepare 2D material inks with variable size distributions, as differences in this parameter could have a significant impact on the electronic behavior of the final material and thus on its field of application. Full article
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Article
Crystal Structure and Supramolecular Architecture of Antiallergic Diphenylene Diethyl Dioxalamates
Crystals 2020, 10(11), 1048; https://doi.org/10.3390/cryst10111048 - 18 Nov 2020
Viewed by 715
Abstract
The crystal structure and the supramolecular architectures of the antiallergic compounds N,N′-(4,4′-methanediyl-di-phenyl)-bis-diethyl dioxalamate (1); N′,N′-(4,4′-oxydi-p-phenylene)-bis-diethyl dioxalamate (2); N,N′-(4,4′-biphenylene)-bis- diethyl dioxalamate (3) are reported. The supramolecular self-assembly in 1-3 is driven [...] Read more.
The crystal structure and the supramolecular architectures of the antiallergic compounds N,N′-(4,4′-methanediyl-di-phenyl)-bis-diethyl dioxalamate (1); N′,N′-(4,4′-oxydi-p-phenylene)-bis-diethyl dioxalamate (2); N,N′-(4,4′-biphenylene)-bis- diethyl dioxalamate (3) are reported. The supramolecular self-assembly in 1-3 is driven by N-H···O=C hydrogen bonds and reinforced by C-H···O=C, C-H···π and C=O···C=O interactions. The three compounds preferred to form cross-linked supramolecular architectures. Intermolecular interactions also were studied by the Hirshfeld surface analysis, revealing that the H···H, O···H, and C···H are the more dominant contacts in the three compounds. The knowledge of crystal structure will allow us to perform theoretical studies to evaluate the antiallergic activity of compounds 1-3. Full article
(This article belongs to the Special Issue Hydrogen Bonds in Crystals)
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Article
Crack Propagation Behavior of a Ni-Based Single-Crystal Superalloy during In Situ SEM Tensile Test at 1000 °C
Crystals 2020, 10(11), 1047; https://doi.org/10.3390/cryst10111047 - 17 Nov 2020
Cited by 1 | Viewed by 916
Abstract
An in situ scanning electron microscope (SEM) tensile test for Ni-based single-crystal superalloy was carried out at 1000 °C. The stress displacement was obtained, and the yield strength and tensile strength of the superalloy were 699 MPa and 826 MPa, respectively. The crack [...] Read more.
An in situ scanning electron microscope (SEM) tensile test for Ni-based single-crystal superalloy was carried out at 1000 °C. The stress displacement was obtained, and the yield strength and tensile strength of the superalloy were 699 MPa and 826 MPa, respectively. The crack propagation process, consisting of Model I crack and crystallographic shearing crack, was determined. More interestingly, the crack propagation path and rate affected by eutectics was directly observed and counted. Results show that the coalescence of the primary crack and second microcrack at the interface of a γ/γ′ matrix and eutectics would make the crack propagation rate increase from 0.3 μm/s to 0.4 μm/s. On the other hand, crack deflection decreased the rate to 0.05 μm/s. Moreover, movement of dislocations in front of the crack was also analyzed to explain the different crack propagation behavior in the superalloy. Full article
(This article belongs to the Special Issue Microstructural and Mechanical Characterization of Alloys Volume II)
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Article
Enhanced Dissolution Efficiency of Tamoxifen Combined with Methacrylate Copolymers in Amorphous Solid Dispersions
Crystals 2020, 10(11), 1046; https://doi.org/10.3390/cryst10111046 - 17 Nov 2020
Viewed by 935
Abstract
Amorphous solid dispersions (SDs) containing poorly soluble tamoxifen dispersed in a meth(acrylate) copolymer combination were proposed as a controlled release system. The objective of this work was to investigate the characteristics and performance of the tamoxifen–polymer mixture and evaluate the changes in functionality [...] Read more.
Amorphous solid dispersions (SDs) containing poorly soluble tamoxifen dispersed in a meth(acrylate) copolymer combination were proposed as a controlled release system. The objective of this work was to investigate the characteristics and performance of the tamoxifen–polymer mixture and evaluate the changes in functionality through a supersaturating dissolution study condition while comparing it to a physical mixture at a fixed drug-loading proportion. Two polymers, Eudragit® L 100 and Eudragit® RL 100, were used to prepare SDs with a 1:1 polymer ratio, containing 10%, 20%, or 30% (wt/wt%) of tamoxifen, by the solvent evaporation method. A physical mixture containing 30% of tamoxifen was also prepared for comparison. SDs were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy. Dissolution tests were conducted under non-sink conditions to verify the occurrence of drug recrystallization upon its release. Solid-state characterizations confirmed that the drug was in the amorphous state within the polymeric matrix. Tamoxifen release in an acidic medium was mainly affected by the increase in drug concentration caused by the possible loss of interactions that characterize the main polymer functionalities. At pH 7.4, supersaturation was slowly achieved while also contributing to the increase in the kinetic solubility of the drug. The physical mixture demonstrated the best overall performance, suggesting that the polymeric interactions may have negatively affected the drug release. The combination of polymers in the composing SD proved to be a promising strategy to tailor the delivery of poorly soluble drugs. Our study highlights important information on the behavior of tamoxifen as a poorly soluble drug in supersaturating dissolution conditions while released from SD systems. Full article
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Article
Graded Grain Structure to Improve Hydrogen-Embrittlement Resistance of TWIP Steel
Crystals 2020, 10(11), 1045; https://doi.org/10.3390/cryst10111045 - 17 Nov 2020
Cited by 1 | Viewed by 787
Abstract
The high strength of twinning-induced plasticity (TWIP) steels makes them vulnerable to the hydrogen embrittlement (HE) phenomenon, thereby limiting their potential applications. This study suggests inducing a graded grain structure (GGS) in a Fe-17Mn-0.8C TWIP steel through shot peening and subsequent heat treatment [...] Read more.
The high strength of twinning-induced plasticity (TWIP) steels makes them vulnerable to the hydrogen embrittlement (HE) phenomenon, thereby limiting their potential applications. This study suggests inducing a graded grain structure (GGS) in a Fe-17Mn-0.8C TWIP steel through shot peening and subsequent heat treatment to solve the problem. The microstructures and fracture surfaces of GGS TWIP steel were compared with those of conventionally manufactured TWIP steel possessing a uniform grain structure (UGS). Compared with the conventional UGS TWIP steel, GGS steel showed similar tensile properties with a yield strength of 310 MPa, tensile strength of 1060 MPa, and elongation-to-failure of 135%. It also exhibited moderately enhanced low-cycle fatigue (LCF) resistance in terms of fatigue life (8196 cycles to failure) compared with the UGS steel (7201 cycles). Furthermore, GGS TWIP steel exhibited a marked improvement in HE resistance, both in the monotonic (by a slow-strain-rate test) and cyclic deformation modes (by the LCF test) in a hydrogen environment. A relatively fine-grained (d = 15.6 μm) surficial area enhanced the HE resistance by inhibiting hydrogen penetration and decreasing twin density, while the coarse-grained (d = 74.6 μm) interior promoted the LCF resistance by suppressing crack growth. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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Article
Mesomorphic, Optical and DFT Aspects of Near to Room-Temperature Calamitic Liquid Crystal
Crystals 2020, 10(11), 1044; https://doi.org/10.3390/cryst10111044 - 16 Nov 2020
Cited by 8 | Viewed by 947
Abstract
A new liquid crystalline, optical material-based Schiff base core with a near to room-temperature mesophase, (4-methoxybenzylideneamino)phenyl oleate (I), was prepared from a natural fatty acid derivative, and its physical and chemical properties investigated by experimental and theoretical approaches. The molecular structure was confirmed [...] Read more.
A new liquid crystalline, optical material-based Schiff base core with a near to room-temperature mesophase, (4-methoxybenzylideneamino)phenyl oleate (I), was prepared from a natural fatty acid derivative, and its physical and chemical properties investigated by experimental and theoretical approaches. The molecular structure was confirmed by elemental analysis, FT-IR (Fourier-Transform-Infrared Spectroscopy) and NMR (nuclear magnetic resonance) spectroscopy. Optical and mesomorphic activities were characterized by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The results show that compound (I) exhibits an enantiotropic monomorphic phase comprising a smectic A phase within the near to room-temperature range. Ordinary and extraordinary refractive indices as well as birefringence with changeable temperatures were analyzed. Microscopic and macroscopic order parameters were also calculated. Theoretical density functional theory (DFT) calculations were carried out to estimate the geometrical molecular structures of the prepared compounds, and the DFT results were used to illustrate the mesomorphic results and optical characteristics in terms of their predicted data. Three geometrical isomers of the prepared compound were investigated to predict the most stable isomer. Many parameters were affected by the geometrical isomerism such as aspect ratio, planarity, and dipole moment. Thermal parameters of the theoretical calculations revealed that the highest co-planar aromatic core is the most stable conformer. Full article
(This article belongs to the Special Issue Optical and Molecular Aspects of Liquid Crystals)
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Article
Structural and Electrochemical Analysis of Decarburized Graphene Electrodes for Supercapacitor Applications
Crystals 2020, 10(11), 1043; https://doi.org/10.3390/cryst10111043 - 16 Nov 2020
Cited by 6 | Viewed by 987
Abstract
In this research, a facile and cost-effective method of graphene synthesis by the modified carburization process and its applications for supercapacitor electrodes is reported. In this simple approach, carbon was diffused into nickel foam and naturally cooled to obtain carbon precipitation for the [...] Read more.
In this research, a facile and cost-effective method of graphene synthesis by the modified carburization process and its applications for supercapacitor electrodes is reported. In this simple approach, carbon was diffused into nickel foam and naturally cooled to obtain carbon precipitation for the in situ growth of graphene by decarburization. Phase-structure and surface-morphology analysis revealed the presence of a highly reduced structure of the graphene layer. Furthermore, the large-intensity D, substantial G, and 2D bands in Raman spectra were attributed to disordered multilayer graphene. The three-electrode systems were used to measure electrochemical efficiency. The electrode sample exhibited enhanced current density of 0.6 A/g, electrode energy of 1.0008 Wh/kg, and power density of 180 W/kg, showing significant electrochemical performance for supercapacitor electrode applications. Full article
(This article belongs to the Section Inorganic Crystalline Materials)
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Article
Reproducible Orientation Relationships Developed from Phase Transformations—Role of Interfaces
Crystals 2020, 10(11), 1042; https://doi.org/10.3390/cryst10111042 - 16 Nov 2020
Cited by 2 | Viewed by 986
Abstract
The orientation relationship (OR) between phases related by a phase transformation is often reproducible. This study interprets and predicts the reproducible ORs with a two-stage approach. The initial OR formed at the nucleation stage tends to allow a periodic structure of a preferred [...] Read more.
The orientation relationship (OR) between phases related by a phase transformation is often reproducible. This study interprets and predicts the reproducible ORs with a two-stage approach. The initial OR formed at the nucleation stage tends to allow a periodic structure of a preferred state to form in the interface. A matching correspondence of either a one-to-one or n-to-m nature can be specified in the periodic structure. An initial OR will become the final reproducible OR if there is no misfit. Otherwise, a reproducible OR developed at the growth stage tends to permit a singular dislocation structure to form in an interface where the preferred state must be sustained locally. The actual change in the OR is subject to the given material system and the phase-transformation condition. Various singular dislocation structures and their constraints on the ORs are analyzed, with thermodynamics and kinetics applied conceptually. The resulting ORs can be specified by following one or more Δg parallelism rules. A set of workable steps is provided to facilitate the interpretation of observed reproducible ORs. Some unsolved problems are identified, which call for further studies that can quantitatively combine the thermodynamics, kinetics and crystallography of phase transformations. Full article
(This article belongs to the Special Issue Crystallography of Structural Phase Transformations)
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Article
The Genetic Algorithm: Using Biology to Compute Liquid Crystal Director Configurations
Crystals 2020, 10(11), 1041; https://doi.org/10.3390/cryst10111041 - 16 Nov 2020
Cited by 2 | Viewed by 950 | Correction
Abstract
The genetic algorithm is an optimization routine for finding the solution to a problem that requires a function to be minimized. It accomplishes this by creating a population of solutions and then producing “offspring” solutions from this population by combining two “parental” solutions [...] Read more.
The genetic algorithm is an optimization routine for finding the solution to a problem that requires a function to be minimized. It accomplishes this by creating a population of solutions and then producing “offspring” solutions from this population by combining two “parental” solutions in much the way that the DNA of biological parents is combined in the DNA of offspring. Strengths of the algorithm include that it is simple to implement, no trial solution is required, and the results are fairly accurate. Weaknesses include its slow computational speed and its tendency to find a local minimum that does not represent the global minimum of the function. By minimizing the elastic, surface, and electric free energies, the genetic algorithm is used to compute the liquid crystal director configuration for a wide range of situations, including one- and two-dimensional problems with various forms of boundary conditions, with and without an applied electric field. When appropriate, comparisons are made with the exact solutions. Ways to increase the performance of the algorithm as well as how to avoid various pitfalls are discussed. Full article
(This article belongs to the Special Issue In Celebration of Noel A. Clark’s 80th Birthday)
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Article
Microwave-Assisted vs. Conventional Hydrothermal Synthesis of MoS2 Nanosheets: Application towards Hydrogen Evolution Reaction
Crystals 2020, 10(11), 1040; https://doi.org/10.3390/cryst10111040 - 16 Nov 2020
Cited by 6 | Viewed by 1365
Abstract
Molybdenum sulfide (MoS2) has emerged as a promising catalyst for hydrogen evolution applications. The synthesis method mainly employed is a conventional hydrothermal method. This method requires a longer time compared to other methods such as microwave synthesis methods. There is a [...] Read more.
Molybdenum sulfide (MoS2) has emerged as a promising catalyst for hydrogen evolution applications. The synthesis method mainly employed is a conventional hydrothermal method. This method requires a longer time compared to other methods such as microwave synthesis methods. There is a lack of comparison of the two synthesis methods in terms of crystal morphology and its electrochemical activities. In this work, MoS2 nanosheets are synthesized using both hydrothermal (HT-MoS2) and advanced microwave methods (MW-MoS2), their crystal morphology, and catalytical efficiency towards hydrogen evolution reaction (HER) were compared. MoS2 nanosheet is obtained using microwave-assisted synthesis in a very short time (30 min) compared to the 24 h hydrothermal synthesis method. Both methods produce thin and aggregated nanosheets. However, the nanosheets synthesized by the microwave method have a less crumpled structure and smoother edges compared to the hydrothermal method. The as-prepared nanosheets are tested and used as a catalyst for hydrogen evolution results in nearly similar electrocatalytic performance. Experimental results showed that: HT-MoS2 displays a current density of 10 mA/cm2 at overpotential (−280 mV) compared to MW-MoS2 which requires −320 mV to produce a similar current density, suggesting that the HT-MoS2 more active towards hydrogen evolutions reaction. Full article
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