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Crystals, Volume 10, Issue 1 (January 2020) – 53 articles

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Cover Story (view full-size image) Stress–strain calculations are presented for nanoindentations made in two otherwise disparate [...] Read more.
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Open AccessArticle
Crystal Structural Analysis of DL-Mandelate Salt of Carvedilol and Its Correlation with Physicochemical Properties
Crystals 2020, 10(1), 53; https://doi.org/10.3390/cryst10010053 - 20 Jan 2020
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Abstract
A 1:1 salt of carvedilol (CVD), an anti-hypertensive drug, with DL-mandelic acid (DL-MA) was crystallized from ethanol and the structure was characterized by X-ray single-crystal diffraction, revealing salt formation by transfer of an acidic proton from the COOH group of MA to the [...] Read more.
A 1:1 salt of carvedilol (CVD), an anti-hypertensive drug, with DL-mandelic acid (DL-MA) was crystallized from ethanol and the structure was characterized by X-ray single-crystal diffraction, revealing salt formation by transfer of an acidic proton from the COOH group of MA to the aliphatic (acyclic) secondary amino NH group of CVD. The crystal structure is triclinic, with a P-1 space group and unit cell parameters a = 9.8416(5) Å, b = 11.4689(5) Å, c = 14.0746(7) Å, α = 108.595(8), β = 95.182(7), γ = 107.323(8), V = 1406.95(15) Å3, and Z = 2. The asymmetric unit contained one protonated CVD and one MA anion, linked via an N+–H∙∙∙O¯ strong hydrogen bond and a ratio of 1:1. As previously reported, the thermal, spectroscopic, and powder X-ray diffraction properties of the salt of CVD with DL-MA (CVD_DL-MA) differed from CVD alone. The intrinsic dissolution rate of CVD_DL-MA was about 10.7 times faster than CVD alone in a pH 6.8 buffer. Full article
(This article belongs to the Special Issue Pharmaceutical Crystals and Its Application)
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Open AccessArticle
Creep of Heusler-Type Alloy Fe-25Al-25Co
Crystals 2020, 10(1), 52; https://doi.org/10.3390/cryst10010052 - 20 Jan 2020
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Abstract
Creep of an alloy based on the intermetallic compound Fe2AlCo was studied by compressive creep tests in the temperature range from 873 to 1073 K. The stress exponent n and the activation energy of creep Q were determined using the multivariable [...] Read more.
Creep of an alloy based on the intermetallic compound Fe2AlCo was studied by compressive creep tests in the temperature range from 873 to 1073 K. The stress exponent n and the activation energy of creep Q were determined using the multivariable regression of the creep-rate data and their description by means of sinh equation (Garofalo equation). The evaluated stress exponents indicate that the dislocation climb controls creep deformation. The estimated apparent activation energies for creep are higher than the activation enthalpy for the diffusion of Fe in Fe3Al. This can be ascribed to the changes in crystal lattice and changing microstructure of the alloy. Full article
(This article belongs to the Special Issue Heusler Alloys)
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Open AccessArticle
Features of the Behavior of the Barocaloric Effect near Ferroelectric Phase Transition Close to the Tricritical Point
Crystals 2020, 10(1), 51; https://doi.org/10.3390/cryst10010051 - 19 Jan 2020
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Abstract
A detailed study of the effect of temperature and pressure on heat capacity, entropy and hysteresis phenomena near the ferroelectric phase transition in ammonium sulfate (AS) was performed. An analysis of experimental results within the framework of the phenomenological theory showed that taking [...] Read more.
A detailed study of the effect of temperature and pressure on heat capacity, entropy and hysteresis phenomena near the ferroelectric phase transition in ammonium sulfate (AS) was performed. An analysis of experimental results within the framework of the phenomenological theory showed that taking into account the temperature-dependent part of the anomalous entropy leads to a significant increase in the barocaloric effect (BCE). The maximum values of extensive and intensive BCE near the tricritical point are outstanding: Δ S B C E m a x 85 J/kgK, Δ T A D m a x 12 K and can be achieved at low pressure ∼0.5 GPa. Full article
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Open AccessArticle
Iron-Doped Lithium Tantalate Thin Films Deposited by Magnetron Sputtering: A Study of the Iron Role in the Structure and the Derived Magnetic Properties
Crystals 2020, 10(1), 50; https://doi.org/10.3390/cryst10010050 - 19 Jan 2020
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Abstract
Fe-doped LiTaO3 thin films with a low and high Fe concentration (labeled as LTO:Fe-LC and LTO:Fe-HC, respectively) were deposited by magnetron sputtering from two home-made targets. The dopant directly influenced the crystalline structure of the LiTaO3 thin films, causing the contraction [...] Read more.
Fe-doped LiTaO3 thin films with a low and high Fe concentration (labeled as LTO:Fe-LC and LTO:Fe-HC, respectively) were deposited by magnetron sputtering from two home-made targets. The dopant directly influenced the crystalline structure of the LiTaO3 thin films, causing the contraction of the unit cell, which was related to the incorporation of Fe3+ ions into the LiTaO3 structure, which occupied Li positions. This substitution was corroborated by Raman spectroscopy, where the bands associated with Li-O bonds broadened in the spectra of the samples. Magnetic hysteresis loops, zero-field cooling curves, and field cooling curves were obtained in a vibrating sample magnetometer. The LTO:Fe-HC sample demonstrates superparamagnetic behavior with a blocking temperature of 100 K, mainly associated with the appearance of Fe clusters in the thin film. On the other hand, a room temperature ferromagnetic behavior was found in the LTO:Fe-LC layer where saturation magnetization (3.80 kAm−1) and magnetic coercivities were not temperature-dependent. Moreover, the crystallinity and morphology of the samples were evaluated by X-ray diffraction and scanning electron microscopy, respectively. Full article
(This article belongs to the Section Crystalline Materials)
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Open AccessArticle
Skull Melting Growth and Characterization of (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 Crystals
Crystals 2020, 10(1), 49; https://doi.org/10.3390/cryst10010049 - 19 Jan 2020
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Abstract
(ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 crystals have been grown by directional melt crystallization in a cold crucible. The chemical and phase compositions of the crystals have been characterized using energy dispersion X-ray spectroscopy (EDX), [...] Read more.
(ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 crystals have been grown by directional melt crystallization in a cold crucible. The chemical and phase compositions of the crystals have been characterized using energy dispersion X-ray spectroscopy (EDX), Raman scattering spectroscopy and transmission electron microscopy (TEM). The X-ray photoelectron emission method has been used for determining the valence state of the Ce ions. We show that directional melt crystallization produces an inhomogeneous ceria distribution along the crystal length. The as-grown crystals are mixtures of cubic and rhombohedral zirconia modifications. The rhombohedral phase has an inhomogeneous distribution along crystal length. Melt crystallization does not produce single-phase cubic (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 crystals. The formation of the phase structure in the crystals for different synthesis methods has been discussed. Full article
(This article belongs to the Special Issue Kinetic Processes of Crystal Growth)
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Open AccessEditorial
Liquid Crystals
Crystals 2020, 10(1), 48; https://doi.org/10.3390/cryst10010048 - 18 Jan 2020
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Abstract
Liquid crystals were discovered by Friedrich Reinitzer in 1888 when he observed colors in cholesterol derivatives that are characteristic of highly birefringent materials [...] Full article
(This article belongs to the Section Liquid Crystals)
Open AccessArticle
Crossover from Deformation Twinning to Lattice Dislocation Slip in Metal–Graphene Composites with Bimodal Structures
Crystals 2020, 10(1), 47; https://doi.org/10.3390/cryst10010047 - 17 Jan 2020
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Abstract
Theoretical model is suggested, which describes of a new micromechanism of crossover from deformation twinning to lattice dislocation slip in metal–graphene nanocomposite with a bimodal structure. In the framework of the model, the lattice dislocation slip occurs through emission of lattice dislocations from [...] Read more.
Theoretical model is suggested, which describes of a new micromechanism of crossover from deformation twinning to lattice dislocation slip in metal–graphene nanocomposite with a bimodal structure. In the framework of the model, the lattice dislocation slip occurs through emission of lattice dislocations from the disclinated grain boundary fragments between a nanocrystalline metal–matrix and large (micrometer-size) grains providing the plastic deformation of bimodal metal–graphene nanocomposite. It is shown that the lattice dislocation emission serves as an effective stress relaxation channel being in competition with nanocrack generation. Full article
(This article belongs to the Special Issue Deformation and Fracture in Nanostructured Materials)
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Open AccessEditorial
New Trends in Protein Crystallization and Protein Crystallography
Crystals 2020, 10(1), 46; https://doi.org/10.3390/cryst10010046 - 17 Jan 2020
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Abstract
Biological crystals and their properties have recently unveiled the complex mechanisms where life is supported [...] Full article
Open AccessEditorial
Acknowledgement to Reviewers of Crystals in 2019
Crystals 2020, 10(1), 45; https://doi.org/10.3390/cryst10010045 - 17 Jan 2020
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Open AccessArticle
Hardening and Creep of Ion Irradiated CLAM Steel by Nanoindentation
Crystals 2020, 10(1), 44; https://doi.org/10.3390/cryst10010044 - 17 Jan 2020
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Abstract
Ion irradiation, combined with nanoindentation, has long been recognized as an effective way to study effects of irradiation on the mechanical properties of metallic materials. In this research, hardening and creep of ion irradiated Chinese low activation martensitic (CLAM) steel are investigated by [...] Read more.
Ion irradiation, combined with nanoindentation, has long been recognized as an effective way to study effects of irradiation on the mechanical properties of metallic materials. In this research, hardening and creep of ion irradiated Chinese low activation martensitic (CLAM) steel are investigated by nanoindentation. Firstly, it is demonstrated that ion irradiation results in the increase of hardness, because irradiation-induced defects impede the glide of dislocations. Secondly, the unirradiated CLAM steel shows indentation creep size effect (ICSE) that the indentation creep strain decreases with the applied load, and ICSE is found to be associated with the variations of geometrical necessary dislocations (GNDs) density. However, ion irradiation results in the alleviation of ICSE due to the irradiation hardening. Thirdly, ion irradiation accelerates nanoindentation creep due to the large numbers of irradiation-induced vacancies whose diffusion controls creep deformation. Meanwhile, owing to the annihilation of vacancies, ion irradiation has a significant influence on the primary creep while only negligible influence has been observed for the steady-state creep. Full article
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Open AccessArticle
Interplay between Convective and Viscoelastic Forces Controls the Morphology of In Vitro Paclitaxel-Stabilized Microtubules
Crystals 2020, 10(1), 43; https://doi.org/10.3390/cryst10010043 - 17 Jan 2020
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Abstract
Microtubules (MTs) are self-assembling, high-aspect-ratio tubular nanostructures formed from the polymerization of tubulin protein. MTs are capable of globally assembling into optically birefringent morphologies, but there is disagreement on the mechanisms driving this behavior. We investigated the temporal evolution of paclitaxel (PTX)-stabilized MT [...] Read more.
Microtubules (MTs) are self-assembling, high-aspect-ratio tubular nanostructures formed from the polymerization of tubulin protein. MTs are capable of globally assembling into optically birefringent morphologies, but there is disagreement on the mechanisms driving this behavior. We investigated the temporal evolution of paclitaxel (PTX)-stabilized MT solutions under a range of in vitro conditions. Significant morphological differences were observed in the polymerized PTX-MT solutions as a consequence of varying the orientation of the reaction vessel (vertical vs. horizontal), the type of heating source (hot plate vs. incubator), the incubation time, and the concentration of PTX (high vs. low). The most robust birefringent patterns were found only in vertically oriented cuvettes that were heated asymmetrically on a hot plate, suggesting dependence upon a convective flow, which we confirmed with a combination of optical and thermal imaging. Higher concentrations of PTX led to denser PTX-MT domain formation and brighter birefringence, due to more complete polymerization. Combining our experimental observations, we conclude that birefringent patterns arise principally through a combination of convective and viscoelastic forces, and we identify the sequence of dynamical stages through which they evolve. Full article
(This article belongs to the Special Issue Nematic Liquid Crystals)
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Open AccessArticle
Co-Crystal Structures of Furosemide:Urea and Carbamazepine:Indomethacin Determined from Powder X-Ray Diffraction Data
Crystals 2020, 10(1), 42; https://doi.org/10.3390/cryst10010042 - 17 Jan 2020
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Abstract
Co-crystallization is a promising approach to improving both the solubility and the dissolution rate of active pharmaceutical ingredients. Crystal structure determination from powder diffraction data plays an important role in determining co-crystal structures, especially those generated by mechanochemical means. Here, two new structures [...] Read more.
Co-crystallization is a promising approach to improving both the solubility and the dissolution rate of active pharmaceutical ingredients. Crystal structure determination from powder diffraction data plays an important role in determining co-crystal structures, especially those generated by mechanochemical means. Here, two new structures of pharmaceutical interest are reported: a 1:1 co‑crystal of furosemide with urea formed by liquid-assisted grinding and a second polymorphic form of a 1:1 co‑crystal of carbamazepine with indomethacin, formed by solvent evaporation. Energy minimization using dispersion-corrected density functional theory was used in finalizing both structures. In the case of carbamazepine:indomethacin, this energy minimization step was essential in obtaining a satisfactory final Rietveld refinement. Full article
(This article belongs to the Special Issue Crystal Structure Characterization by Powder Diffraction)
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Open AccessArticle
In Situ TEM Crystallization of Amorphous Iron Particles
Crystals 2020, 10(1), 41; https://doi.org/10.3390/cryst10010041 - 17 Jan 2020
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Abstract
Even though sub-micron and nano-sized iron particles generally display single or polycrystalline structures, a growing interest has also been dedicated to the class of amorphous ones, whose absence of a crystal structure is capable of modifying their physical properties. Among the several routes [...] Read more.
Even though sub-micron and nano-sized iron particles generally display single or polycrystalline structures, a growing interest has also been dedicated to the class of amorphous ones, whose absence of a crystal structure is capable of modifying their physical properties. Among the several routes so far described to prepare amorphous iron particles, we report here about the crystallization of those prepared by chemical reduction of Fe3+ ions using NaBH4, with sizes ranging between 80 and 200 nm and showing a high stability against oxidation. Their crystallization was investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD), and in situ heating transmission electron microscopy (TEM). The latter technique was performed by the combined use of electron diffraction of a selected sample area, and bright and dark field TEM imaging, and allowed determining that the crystallization turns the starting amorphous particles into polycrystalline α-Fe ones. Also, under the high vacuum of the TEM column, the crystallization temperature of the particles shifted to 550 °C from the 465 °C, previously observed by DSC and XRD under 105 Pa of Ar. This indicates the pivotal role of the external pressure in influencing the starting point of phase transition. Conversely, upon both the DSC/XRD pressure and the TEM vacuum conditions, the mean size of the crystal domains increases as a consequence of further thermal increase, even if with some pressure-related differences. Full article
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Open AccessArticle
Stability-Ranking of Crystalline Ice Polymorphs Using Density-Functional Theory
Crystals 2020, 10(1), 40; https://doi.org/10.3390/cryst10010040 - 16 Jan 2020
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Abstract
In this work, we consider low-enthalpy polymorphs of ice, predicted previously using a modified basin-hopping algorithm for crystal-structure prediction with the TIP4P empirical potential at three pressures (0, 4 and 8 kbar). We compare and (re)-rank the reported ice polymorphs in order of [...] Read more.
In this work, we consider low-enthalpy polymorphs of ice, predicted previously using a modified basin-hopping algorithm for crystal-structure prediction with the TIP4P empirical potential at three pressures (0, 4 and 8 kbar). We compare and (re)-rank the reported ice polymorphs in order of energetic stability, using high-level quantum-chemical calculations, primarily in the guise of sophisticated Density-Functional Theory (DFT) approaches. In the absence of applied pressure, ice Ih is predicted to be energetically more stable than ice Ic, and TIP4P-predicted results and ranking compare well with the results obtained from DFT calculations. However, perhaps not unexpectedly, the deviation between TIP4P- and DFT-calculated results increases with applied external pressure. Full article
(This article belongs to the Section Crystalline Materials)
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Open AccessArticle
Controllable Synthesis of Metal-Organic Framework/Polyethersulfone Composites
Crystals 2020, 10(1), 39; https://doi.org/10.3390/cryst10010039 - 15 Jan 2020
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Abstract
Composite materials that contain metal-organic frameworks (MOFs) as a filler and a polymer matrix have attracted attention because they present a combination of high porosity and structural integrity. Phase compatibilities of the MOF and polymer play a vital role in the formation of [...] Read more.
Composite materials that contain metal-organic frameworks (MOFs) as a filler and a polymer matrix have attracted attention because they present a combination of high porosity and structural integrity. Phase compatibilities of the MOF and polymer play a vital role in the formation of the composites. In particular, the stiff polymer cannot easily adapt to penetrate into the surface pore of MOF and mainly depends on chemical attractions to form the MOF/polymer composites. We report the synthesis of MOF/polyethersulfone (Young’s modulus = ~2.6 GPa) via different fabrication methods, different MOF types and particle sizes, and different solvents. The formed network structures are robust, monolithic composites with 60% MOF loadings; also, the MOF surface area and porosity were fully preserved. The study explored the formation of the composite between MOF and a stiff polymer and encourages the design of more MOF/polymer composite materials across a wide range of applications. Full article
(This article belongs to the Section Crystalline Materials)
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Open AccessReview
Raman Scattering: From Structural Biology to Medical Applications
Crystals 2020, 10(1), 38; https://doi.org/10.3390/cryst10010038 - 15 Jan 2020
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Abstract
This is a review of relevant Raman spectroscopy (RS) techniques and their use in structural biology, biophysics, cells, and tissues imaging towards development of various medical diagnostic tools, drug design, and other medical applications. Classical and contemporary structural studies of different water-soluble and [...] Read more.
This is a review of relevant Raman spectroscopy (RS) techniques and their use in structural biology, biophysics, cells, and tissues imaging towards development of various medical diagnostic tools, drug design, and other medical applications. Classical and contemporary structural studies of different water-soluble and membrane proteins, DNA, RNA, and their interactions and behavior in different systems were analyzed in terms of applicability of RS techniques and their complementarity to other corresponding methods. We show that RS is a powerful method that links the fundamental structural biology and its medical applications in cancer, cardiovascular, neurodegenerative, atherosclerotic, and other diseases. In particular, the key roles of RS in modern technologies of structure-based drug design are the detection and imaging of membrane protein microcrystals with the help of coherent anti-Stokes Raman scattering (CARS), which would help to further the development of protein structural crystallography and would result in a number of novel high-resolution structures of membrane proteins—drug targets; and, structural studies of photoactive membrane proteins (rhodopsins, photoreceptors, etc.) for the development of new optogenetic tools. Physical background and biomedical applications of spontaneous, stimulated, resonant, and surface- and tip-enhanced RS are also discussed. All of these techniques have been extensively developed during recent several decades. A number of interesting applications of CARS, resonant, and surface-enhanced Raman spectroscopy methods are also discussed. Full article
(This article belongs to the Special Issue Raman Spectroscopy of Crystals)
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Open AccessArticle
Stability and Phase Transitions of Nontoxic γ-Cyclodextrin-K+ Metal-Organic Framework in Various Solvents
Crystals 2020, 10(1), 37; https://doi.org/10.3390/cryst10010037 - 15 Jan 2020
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Abstract
Cyclodextrin (CD) has been used to prepare biocompatible and nontoxic metal-organic frameworks (MOFs) suitable for biomedical applications as drug carriers. In this study, γ-CD/K-based MOF (γ-CD-MOF-1-α) was synthesized and its stability in various solvents was explored by single-crystal X-ray diffractometry (SCXRD) and powder [...] Read more.
Cyclodextrin (CD) has been used to prepare biocompatible and nontoxic metal-organic frameworks (MOFs) suitable for biomedical applications as drug carriers. In this study, γ-CD/K-based MOF (γ-CD-MOF-1-α) was synthesized and its stability in various solvents was explored by single-crystal X-ray diffractometry (SCXRD) and powder X-ray diffractometry (PXRD). As a result of solvent-induced phase transformations, two novel crystalline phases of γ-CD-MOF-1 were discovered. The newly formed ε- and δ-phases crystallize in orthorhombic and tetragonal symmetry, respectively. In ε-phase, toluene was determined as a guest molecule by SCXRD. Interactions between γ-cyclodextrin and solvent molecules in ε-phase were evaluated using Hirshfeld surface analysis. The thermal stability of the new crystal forms of γ-CD-MOF-1 was analyzed by differential scanning calorimetry and thermogravimetric analysis. Full article
(This article belongs to the Section Crystalline Materials)
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Open AccessArticle
Morpholino-Substituted BODIPY Species: Synthesis, Structure and Electrochemical Studies
Crystals 2020, 10(1), 36; https://doi.org/10.3390/cryst10010036 - 14 Jan 2020
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Abstract
Functionalization of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) chromophores at the 2,6-positions with iodo substituents and morpholino-substituted α-methyl groups affords molecules with strong absorbance in the visible spectrum. The effect of such substitution on the solid-state arrangements, absorption, fluorescence and electronic properties of these dye molecules is [...] Read more.
Functionalization of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) chromophores at the 2,6-positions with iodo substituents and morpholino-substituted α-methyl groups affords molecules with strong absorbance in the visible spectrum. The effect of such substitution on the solid-state arrangements, absorption, fluorescence and electronic properties of these dye molecules is reported. The spectroscopic and spectroelectrochemical measurements display intense absorptions in the UV-visible spectrum with bathochromic shifts, in comparison to unfunctionalized BODIPY, and a positive shift in redox potentials due to functionalisation of the BODIPY core. Halogen bonds are observed in the solid-state structures of both halogenated BODIPY species, which in one case leads to the formation of an unusual halogen bonded framework. Full article
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Open AccessArticle
Incorporation of Cd-Doping in SnO2
Crystals 2020, 10(1), 35; https://doi.org/10.3390/cryst10010035 - 13 Jan 2020
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Abstract
Tuning the electrical properties of materials by controlling their doping content has been utilized for decades in semiconducting oxides. Here, an atomistic view is successfully employed to obtain local information on the charge distribution and point defects in Cd-doped SnO2. We [...] Read more.
Tuning the electrical properties of materials by controlling their doping content has been utilized for decades in semiconducting oxides. Here, an atomistic view is successfully employed to obtain local information on the charge distribution and point defects in Cd-doped SnO2. We present a study that uses the time-differential perturbed gamma–gamma angular correlations (TDPAC) method in samples prepared by using a sol–gel approach. The hyperfine field parameters are presented as functions of the annealing temperature in pellet samples to show the evolution of incorporating Cd dopants into the crystal lattice. Additionally, the system was characterized with X-ray fluorescence, electron dispersive spectroscopy, and scanning electron microscopy after the probe nuclei 111In(111Cd) decayed. The TDPAC results reveal that the probe ions were incorporated into two different local environments of the SnO2 lattice at temperatures up to 973 K for cation substitutional sites. Full article
(This article belongs to the Special Issue Defects in Crystals)
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Open AccessArticle
On the Nitrogen Doping in Erbium and Nitrogen Codoped Magnesium Zinc Oxide Diode by Spray Pyrolysis
Crystals 2020, 10(1), 34; https://doi.org/10.3390/cryst10010034 - 12 Jan 2020
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Abstract
Diodes with an erbium and nitrogen codoped magnesium zinc oxide (MgZnO:Er,N) active layer were fabricated by spray pyrolysis on Si substrate with aqueous solutions including magnesium nitrate, zinc acetate, erbium acetate, ammonium acetate, and indium nitrate precursors. Diodes with different nitrogen content in [...] Read more.
Diodes with an erbium and nitrogen codoped magnesium zinc oxide (MgZnO:Er,N) active layer were fabricated by spray pyrolysis on Si substrate with aqueous solutions including magnesium nitrate, zinc acetate, erbium acetate, ammonium acetate, and indium nitrate precursors. Diodes with different nitrogen content in their precursor were prepared and their properties were investigated. With scanning electron microscopy, film surface with mixed hexagonal flakes and tiny blocks was characterized for all samples. Certain morphologies varied for samples with different N contents. In the photoluminescence analyses, the intensity of the oxygen-related defects peak increased with the increasing of nitrogen content. The diodes were fabricated with an Au and In deposition on the top and backside. The diode current–voltage as well as capacitance–voltage characteristics were examined. An ununiformed n-type concentration distribution with high concentration near the interface in the MgZnO:Er,N layer was characterized for all samples. Diodes with high nitrogen content exhibit reduced breakdown voltage and higher interface concentration characteristics. Under reversed bias conditions with an injection current of 50 mA, a light spectrum with two distinct green emissions around wavelengths 532 and 553 nm was observed. A small spectrum variation was characterized for diodes prepared from different nitrogen content. The diode luminescence characteristics were examined and the diode prepared from N/Zn=1 in the precursor showed an optimal injection current-to-luminescence property. The current and luminescence properties of the diode were characterized and discussed. Full article
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Open AccessArticle
Inhomogeneity and Segregation Effect in the Surface Layer of Fe-Doped SrTiO3 Single Crystals
Crystals 2020, 10(1), 33; https://doi.org/10.3390/cryst10010033 - 10 Jan 2020
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Abstract
The effect of Fe doping on SrTiO3 single crystals was investigated in terms of crystal and electronic structure over a wide temperature range in both oxidizing and reducing conditions. The electrical properties were thoroughly studied with a special focus on the resistive [...] Read more.
The effect of Fe doping on SrTiO3 single crystals was investigated in terms of crystal and electronic structure over a wide temperature range in both oxidizing and reducing conditions. The electrical properties were thoroughly studied with a special focus on the resistive switching phenomenon. Contrary to the undoped SrTiO3 crystals, where isolated filaments are responsible for resistive switching, the iron-doped crystals showed stripe-like conducting regions at the nanoscale. The results showed a non-uniform Fe distribution of as-received crystals and the formation of new phases in the surface layer of reduced/oxidized samples. The oxidation procedure led to a separation of Ti(Fe) and Sr, while the reduction resulted in the tendency of Fe to agglomerate and migrate away from the surface as seen from the time of flight mass spectroscopy measurements. Moreover, a clear presence of Fe-rich nano-filament in the reduced sample was found. Full article
(This article belongs to the Special Issue Electronic Phenomena of Transition Metal Oxides)
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Open AccessCommunication
De novo Phasing Xenons Observed in the Frog Ependymin-Related Protein
Crystals 2020, 10(1), 32; https://doi.org/10.3390/cryst10010032 - 10 Jan 2020
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Abstract
Pressurizing Xe or Kr noble gas into the protein crystal for de novo phasing has been one method of choice when the introduction of other heavy-atom compounds fails. One reason is because, unlike other heavy-atom compounds, their immobilized sites are mostly hydrophobic cavities. [...] Read more.
Pressurizing Xe or Kr noble gas into the protein crystal for de novo phasing has been one method of choice when the introduction of other heavy-atom compounds fails. One reason is because, unlike other heavy-atom compounds, their immobilized sites are mostly hydrophobic cavities. Previously, the structure of frog ependymin-related protein (EPDR) has been determined using a single wavelength anomalous diffraction (SAD) on a Xe-pressurized crystal. Since no report on the four Xe binding sites has been made, these sites are analyzed in this study. Of the four Xe atoms, three are found along the hydrophobic interfaces created by the two crystallographic symmetry mates of EPDR. One final Xe atom occupies a Ca2+-binding site of the native protein entirely stabilized by the polar atoms of the surrounding EDPR residues. We believe that this atypical Xe location is very unique and merits further study. Full article
(This article belongs to the Section Biomolecular Crystals)
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Open AccessArticle
The Electric and Dielectric Properties of SrF2:Tb3+ Nanocrystals Revealed by AC Impedance Spectroscopy
Crystals 2020, 10(1), 31; https://doi.org/10.3390/cryst10010031 - 10 Jan 2020
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Abstract
The electric and dielectric properties of SrF2:Tb3+ nanocrystals were studied by AC impedance spectroscopy. The grain and grain boundary resistances and the complex permittivity with different Tb-doped concentrations were obtained. As the Tb-doping concentration increases, the grain and grain boundary [...] Read more.
The electric and dielectric properties of SrF2:Tb3+ nanocrystals were studied by AC impedance spectroscopy. The grain and grain boundary resistances and the complex permittivity with different Tb-doped concentrations were obtained. As the Tb-doping concentration increases, the grain and grain boundary resistances decrease until 6% and then increase. The Tb doping leads to the increase of interstitial F quantity and the decrease of the activation enthalpy, and finally causes the decreases of grain and grain boundary resistances. When the Tb-doping is larger than 6%, the effect of the deformation potential scattering is dominant, which leads to the increases of grain and grain boundary resistances. The strong dispersion of the permittivity at the low frequencies indicates the carrier was hopping in the transport process. The ε′ and ε″ values at the low frequencies decrease as the sample resistance increases. Full article
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Open AccessArticle
Influence of Crystallization Behavior of Gas Quenching Blast Furnace Slag on the Preparation of Amorphous Slag Beads
Crystals 2020, 10(1), 30; https://doi.org/10.3390/cryst10010030 - 10 Jan 2020
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Abstract
Slag beads with different crystal content could be obtained through the gas quenching blast furnace slag (BFS) process. In order to increase the additional value of the slag beads as much as possible, it was necessary to restrain the crystallization of the slag [...] Read more.
Slag beads with different crystal content could be obtained through the gas quenching blast furnace slag (BFS) process. In order to increase the additional value of the slag beads as much as possible, it was necessary to restrain the crystallization of the slag beads as much as possible. In this paper, the mineral types and crystallization temperatures of BFS with different basicities and cooling rates were studied by using Factsage thermodynamic software, XRD, and differential scanning calorimeter (DSC) experiments, which obtained the gas quenching temperature and the cooling rate needed to restrain crystallization behavior in the gas quenching process; The crystallization mechanism was studied by calculating crystallization activation energy (Ec) using the DSC experiment, at the same time, the thermodynamic results were verified. The proper basicity and cooling rate of BFS were found to be conducive to the preparation of amorphous slag beads. The results showed that the initial crystallization temperature decreased with decreasing the basicity and increasing the cooling rate, which could increase the amorphous content of slag beads in the gas quenching process. The crystallization activation energy (Ec) increased with decreasing basicity, which increased the crystallization barrier. Full article
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Open AccessArticle
Microstructure and Mechanical Properties of Carbon/Carbon Composites Infiltrated with Ti–6Al–4V Titanium Alloy
Crystals 2020, 10(1), 29; https://doi.org/10.3390/cryst10010029 - 08 Jan 2020
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Abstract
In this work, chemical vapor infiltration (CVI) was combined with reactive melt infiltration (RMI) using Ti–6Al–4V titanium alloy powder to prepare Cf/C–TiC composites. The microstructure and composition of Cf/C–TiC composites were characterized by scanning electron microscopy (SEM) and X-ray [...] Read more.
In this work, chemical vapor infiltration (CVI) was combined with reactive melt infiltration (RMI) using Ti–6Al–4V titanium alloy powder to prepare Cf/C–TiC composites. The microstructure and composition of Cf/C–TiC composites were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The flexural properties of the composites were also analyzed. The results indicated that the Ti–6Al–4V titanium alloy infiltrated the Cf/C preform and reacted with the pyrolytic carbon (PyC) to form a TiC–VC and Al4C3 matrix, and no residual Ti, Al, or V was detected. Moreover, Al4C3 was concentrated and independently distributed, whereas Ti and V reacted with C to form a TiC–VC solid solution. The porosity was 6.75%, and the bulk density of Cf/C–TiC was 1.96 g/cm3. The flexural strength, flexural modulus, and failure strains were 256 ± 18 MPa, 89 ± 9 GPa, and 0.93 ± 0.13%, respectively. The work of fracture of the Cf/C–TiC composite was about 6.8 ± 0.38 KJ/m2. Due to the propagation and deflection of cracks, as well as debonding and fiber pullout, the Cf/C–TiC composite showed ductile fracture behavior. Full article
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Open AccessArticle
Determination of the Mechanical Properties of PIN–PMN–PT Bulk Single Crystals by Nanoindentation
Crystals 2020, 10(1), 28; https://doi.org/10.3390/cryst10010028 - 08 Jan 2020
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Abstract
The present study aimed to experimentally evaluate the mechanical properties of Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) bulk single crystals with different crystallographic directions using the nanoindentation technique. The loadindentation depth curves, [...] Read more.
The present study aimed to experimentally evaluate the mechanical properties of Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) bulk single crystals with different crystallographic directions using the nanoindentation technique. The loadindentation depth curves, elastic and plastic deformations, hardnesses, and Young’s moduli of [100]- and [110]-oriented 0.28PIN–0.43PMN–0.29PT bulk single crystals were investigated. Our results show that with an increase in the maximum indentation depth hmax, the plastic residual percentage increased for both the [100]- and the [110]-oriented single crystals. At each hmax, the plastic residual percentage of the [100]-oriented PIN–PMN–PT single crystals was less than that of the [110]-oriented PIN–PMN–PT single crystals. At hmax from 500 nm to 2000 nm, the plastic deformation was larger than the elastic deformation, and the plastic residual percentage was larger than 50% for both the [100]- and the [110]-oriented single crystals. This means that the plastic deformation dominated in the indentation process of PIN–PMN–PT single crystals. The indentation size effect on the hardness of the PIN–PMN–PT single crystals was apparent in the nanoindentation process. Both the hardness and the Young’s modulus of the [100]-PIN–PMN–PT single crystals were greater than those of the [110]-PIN–PMN–PT single crystals, which indicates that the PIN–PMN–PT single crystals had anisotropic mechanical characteristics. Full article
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Open AccessReview
Quantitative Phase Analysis by X-ray Diffraction—Doping Methods and Applications
Crystals 2020, 10(1), 27; https://doi.org/10.3390/cryst10010027 - 07 Jan 2020
Viewed by 268
Abstract
X-ray powder diffraction is an ideal technique for the quantitative analysis of a multiphase sample. The intensities of diffraction lines of a phase in a multiphase sample are proportional to the phase fraction and the quantitative analysis can be obtained if the correction [...] Read more.
X-ray powder diffraction is an ideal technique for the quantitative analysis of a multiphase sample. The intensities of diffraction lines of a phase in a multiphase sample are proportional to the phase fraction and the quantitative analysis can be obtained if the correction for the absorption of X-rays in the sample is performed. Simple procedures of quantitative X-ray diffraction phase analysis of a multiphase sample are presented. The matrix-flushing method, with the application of reference intensities, yields the relationship between the intensity and phase fraction free from the absorption effect, thus, shunting calibration curves or internal standard procedures. Special attention is paid to the doping methods: (i) simultaneous determination of the fractions of several phases using a single doping and (ii) determination of the fraction of the dominant phase. The conditions to minimize systematic errors are discussed. The problem of overlapping of diffraction lines can be overcome by combining the doping method (i) and the individual profile fitting method, thus performing the quantitative phase analysis without the reference to structural models of particular phases. Recent suggestions in quantitative phase analysis are quoted, e.g., in study of the decomposition of supersaturated solid solutions—intermetallic alloys. Round Robin on Quantitative Phase Analysis, organized by the IUCr Commission on Powder Diffraction, is discussed shortly. The doping methods have been applied in various studies, e.g., phase transitions in titanium dioxide, biomineralization processes, and phases in intermetallic oxide systems and intermetallic alloys. Full article
(This article belongs to the Special Issue Crystal Structure Characterization by Powder Diffraction)
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Open AccessArticle
The Temperature Dependence of the Magnetization Process of the Kondo Insulator YbB12
Crystals 2020, 10(1), 26; https://doi.org/10.3390/cryst10010026 - 07 Jan 2020
Viewed by 178
Abstract
The properties of the Kondo insulator in a strong magnetic field are one of the most intriguing subjects in condensed matter physics. The Kondo insulating state is expected to be suppressed by magnetic fields, which results in the dramatic change in the electronic [...] Read more.
The properties of the Kondo insulator in a strong magnetic field are one of the most intriguing subjects in condensed matter physics. The Kondo insulating state is expected to be suppressed by magnetic fields, which results in the dramatic change in the electronic state. We have studied the magnetization process of one of the prototypical Kondo insulators YbB 12 at several temperatures in magnetic fields of up to 80 T. The metamagnetism due to the insulator-metal (IM) transition seen around 50 T was found to become significantly broadened at approximately 30 K. This characteristic temperature T * 30 K in YbB 12 is an order of magnitude lower than the Kondo temperature T K = 240 K. Our results suggest that there is an energy scale smaller than the Kondo temperature that is important to understanding the nature of Kondo insulators. Full article
(This article belongs to the Special Issue Magnetic Field-induced Phase Transition)
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Open AccessArticle
Low Gate Lag Normally-Off p-GaN/AlGaN/GaN High Electron Mobility Transistor with Zirconium Gate Metal
Crystals 2020, 10(1), 25; https://doi.org/10.3390/cryst10010025 - 06 Jan 2020
Viewed by 251
Abstract
The impact of gate metal on the leakage current and breakdown voltage of normally-off p-GaN gate high-electron-mobility-transistor (HEMT) with nickel (Ni) and zirconium (Zr) metals were studied and investigated. In this study, a Zr metal as a gate contact to p-GaN/AlGaN/GaN high mobility [...] Read more.
The impact of gate metal on the leakage current and breakdown voltage of normally-off p-GaN gate high-electron-mobility-transistor (HEMT) with nickel (Ni) and zirconium (Zr) metals were studied and investigated. In this study, a Zr metal as a gate contact to p-GaN/AlGaN/GaN high mobility transistor (HEMT) was first applied to improve the hole accumulation at the high gate voltage region. In addition, the ZrN interface is also beneficial for improving the Schottky barrier with low nitrogen vacancy induced traps. The features of Zr are low work function (4.05 eV) and high melting point, which are two key parameters with p-GaN Schottky contact at reversed voltage. Therefore, Zr/p-GaN interface exhibits highly potential for GaN-based switching power device applications. Full article
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Open AccessArticle
Effect of Molecular Structure of Organic Acids on the Crystal Habit of α-CaSO4·0.5H2O from Phosphogypsum
Crystals 2020, 10(1), 24; https://doi.org/10.3390/cryst10010024 - 06 Jan 2020
Viewed by 195
Abstract
The organic acid crystal modifiers play an important role in the control of the crystal habit of α-hemihydrate gypsum (α-CaSO4·0.5H2O) from phosphogypsum, but the molecular structure characteristics of crystal modifiers have not been clarified, which makes it difficult to [...] Read more.
The organic acid crystal modifiers play an important role in the control of the crystal habit of α-hemihydrate gypsum (α-CaSO4·0.5H2O) from phosphogypsum, but the molecular structure characteristics of crystal modifiers have not been clarified, which makes it difficult to judge whether an organic acid has the ability to regulate the crystal habit of α-CaSO4·0.5H2O directly. In this work, the effect of organic acids with different molecular structures on the crystal habit of α-CaSO4·0.5H2O and its adsorption differences onto the α-CaSO4·0.5H2O surface were explored. The results show that the molecular structure characteristics of crystal modifiers contain two or more carboxylic groups (COOH) that are separated by two methylene or methine groups. Furthermore, organic acids with the regulation ability can adsorb on the surface of α-CaSO4·0.5H2O and change its growth habit. With the increase in the crystal modifier concentration, the α-CaSO4·0.5H2O crystals are shortened in length and enlarged in width, resulting in the decrease in aspect ratio and the increase in compressive strength. Conversely, when the adsorption of ineffective organic acids on the surface of α-CaSO4·0.5H2O was not detected, the α-CaSO4·0.5H2O crystals remained long hexagonal prisms. These results have guiding significance for the screening of novel organic acid crystal modifiers. Full article
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