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Crystals, Volume 9, Issue 2 (February 2019)

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Cover Story (view full-size image) Introducing pyruvic acid and UV radiation into the growing process of silica-carbonate biomorphs [...] Read more.
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Open AccessArticle A Combined Experiment and Crystal Plasticity FEM Study of Microstructure and Texture in Aluminium Processed by Reverse and Unidirectional Accumulative Roll-Bonding
Crystals 2019, 9(2), 119; https://doi.org/10.3390/cryst9020119
Received: 23 January 2019 / Revised: 15 February 2019 / Accepted: 21 February 2019 / Published: 24 February 2019
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Abstract
In this report, reverse accumulative roll-bonding (ARB) was conducted for the first time. It was found that the microstructure after reverse ARB was relatively coarser than that after unidirectional ARB, and texture intensity was slightly weaker. In addition to the experimental study, the [...] Read more.
In this report, reverse accumulative roll-bonding (ARB) was conducted for the first time. It was found that the microstructure after reverse ARB was relatively coarser than that after unidirectional ARB, and texture intensity was slightly weaker. In addition to the experimental study, the crystal plasticity finite element method was applied to the ARB-processed polycrystalline aluminium. The simulation followed the real deformation of reverse ARB and unidirectional ARB, and the predictions were validated by the experimental observations. Compared to the second cycle of unidirectional ARB, the crystal orientations (after the first cycle) were relatively unstable during the second cycle of reverse ARB, which is believed to be the reason for the relatively coarser microstructure after reverse ARB. Full article
(This article belongs to the Section Crystalline Materials)
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Open AccessArticle Hierarchical Core/Shell Structured [email protected](OH)2 Nanospheres as Binder-Free Electrodes for High Performance Supercapacitors
Crystals 2019, 9(2), 118; https://doi.org/10.3390/cryst9020118
Received: 27 January 2019 / Revised: 17 February 2019 / Accepted: 21 February 2019 / Published: 24 February 2019
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Abstract
Hierarchical [email protected](OH)2 nanospheres were achieved directly on copper foam substrate through a convenient two-step process. Ag nanoflowers were formed on copper substrate by galvanic replacement technology between AgNO3 and copper foam followed by electrodeposition of a layer of Ni(OH)2. [...] Read more.
Hierarchical [email protected](OH)2 nanospheres were achieved directly on copper foam substrate through a convenient two-step process. Ag nanoflowers were formed on copper substrate by galvanic replacement technology between AgNO3 and copper foam followed by electrodeposition of a layer of Ni(OH)2. Ag nanostructures as cores not only dominated the final morphology of the composites, but also improved the electrical conductivity, increased the specific surface area of the active electrode material, and even directly participated in the electrochemical reactions. The resulted [email protected](OH)2 nanospheres could be directly used as high-performance binder-free electrodes and exhibited enhanced electrochemical performance with a high specific capacitance of 1.864 F cm−2 and long cycling lifespans of 90.43% capacity retaining after 3000 cycles. Full article
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Open AccessArticle Influence of Selected Saccharides on the Precipitation of Calcium-Vaterite Mixtures by the CO2 Bubbling Method
Crystals 2019, 9(2), 117; https://doi.org/10.3390/cryst9020117
Received: 31 January 2019 / Revised: 15 February 2019 / Accepted: 20 February 2019 / Published: 23 February 2019
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Abstract
Calcium carbonate is a compound existing in living organisms and produced for many biomedical applications. In this work, calcium carbonate was synthesized by a CO2 bubbling method using ammonia as a CO2 absorption promotor. Glucose, fructose, sucrose, and trehalose were added [...] Read more.
Calcium carbonate is a compound existing in living organisms and produced for many biomedical applications. In this work, calcium carbonate was synthesized by a CO2 bubbling method using ammonia as a CO2 absorption promotor. Glucose, fructose, sucrose, and trehalose were added into the reaction mixture to modify characteristics of precipitated calcium carbonate particles. To determine the polymorphic form of produced calcium carbonate particles, Fourier transform infrared spectroscopy (FTIR-ATR) and X-ray diffraction (XRD) analysis were performed. Scanning electron microscopy (SEM) was used to estimate the size and shape of produced particles. Mixtures of vaterite and calcite were synthesized in all experiments. The percentage content of the vaterite in the samples depended on used additive. The highest concentration of vaterite (90%) was produced from a solution containing sucrose, while the lowest concentration (2%) was when fructose was added. Saccharides affected the rate of CO2 absorption, which resulted in a change in the precipitation rate and, therefore, the polymorphic composition of calcium carbonate obtained in the presence of saccharides was more varied. Full article
(This article belongs to the Section Crystalline Materials)
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Open AccessArticle Solvent Effects on the Spin Crossover Properties of Iron(II) Imidazolylimine Complexes
Crystals 2019, 9(2), 116; https://doi.org/10.3390/cryst9020116
Received: 23 January 2019 / Revised: 19 February 2019 / Accepted: 20 February 2019 / Published: 22 February 2019
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Abstract
A series of Fe(II) complexes, fac-[Fe(4-ima-Bp)3](Y)2⋅sol (Y = ClO4; sol = 3EtOH 1, 3MeOH 2; Y= BF4; sol = EtOH⋅4H2O 3, 4H2O 4 and 3.5MeCN 5) [...] Read more.
A series of Fe(II) complexes, fac-[Fe(4-ima-Bp)3](Y)2⋅sol (Y = ClO4; sol = 3EtOH 1, 3MeOH 2; Y= BF4; sol = EtOH⋅4H2O 3, 4H2O 4 and 3.5MeCN 5) have been prepared and structurally and magnetically characterized. The low temperature structures of 1, 2 and 5 have been determined by X-ray crystallography with LS Fe(II) centres found in all cases. Extensive C–H···π interactions between the cations form 2D layers, which are linked to one another through N-H···O and O-H···O hydrogen bonds, resulting in high cooperativity. Despite 5 containing MeCN, N-H···O/F hydrogen bonds, and C–H···π and π-π interactions combine to give similar 2D layers. Magnetic measurements reveal moderately abrupt spin crossover for 1-4; becoming more gradual and only 50% complete in 1 due to solvent loss. The MeCN solvate shows more gradual SCO and reinforces how subtle changes in packing can significantly influence SCO behaviour. Full article
(This article belongs to the Special Issue Synthesis and Applications of New Spin Crossover Compounds)
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Open AccessArticle Radiation Defects in Heterostructures 3C-SiC/4H-SiC
Crystals 2019, 9(2), 115; https://doi.org/10.3390/cryst9020115
Received: 21 January 2019 / Revised: 20 February 2019 / Accepted: 20 February 2019 / Published: 22 February 2019
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Abstract
The effect of 8 MeV proton irradiation on n-3C-SiC epitaxial layers grown by sublimation on semi-insulating 4H-SiC substrates has been studied. Changes in sample parameters were recorded using the Hall-effect method and judged from photoluminescence spectra. It was found [...] Read more.
The effect of 8 MeV proton irradiation on n-3C-SiC epitaxial layers grown by sublimation on semi-insulating 4H-SiC substrates has been studied. Changes in sample parameters were recorded using the Hall-effect method and judged from photoluminescence spectra. It was found that the carrier removal rate (Vd) in 3C-SiC is ~100 cm−1, which is close to Vd in 4H-SiC. Compared with 4H and 6H silicon carbide, no significant increase in the intensity of the so-called defect-related photoluminescence was observed. An assumption is made that radiation-induced compensation processes in 3C-SiC are affected by structural defects (twin boundaries), which are always present in epitaxial cubic silicon carbide layers grown on substrates of the hexagonal polytypes. Full article
(This article belongs to the Special Issue Development and Investigation of SiC and SiC-based Devices)
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Open AccessArticle Different Roles of Ce3+ Optical Centers in Oxyorthosilicate Nanocrystals at X-ray and UV Excitation
Crystals 2019, 9(2), 114; https://doi.org/10.3390/cryst9020114
Received: 17 January 2019 / Revised: 6 February 2019 / Accepted: 19 February 2019 / Published: 21 February 2019
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Abstract
Luminescence properties of Lu2SiO5:Ce3+ and Y2SiO5:Ce3+ nanocrystals were studied using photo- and X-ray luminescence techniques. The crystal structure of Re2SiO5 nanocrystals (P21/c space group) differs from the crystal [...] Read more.
Luminescence properties of Lu2SiO5:Ce3+ and Y2SiO5:Ce3+ nanocrystals were studied using photo- and X-ray luminescence techniques. The crystal structure of Re2SiO5 nanocrystals (P21/c space group) differs from the crystal structure of Re2SiO5 bulk crystals (C2/c space group) with 9- and 7-oxygen-coordinated cation positions instead of 6- and 7-coordinated ones observed for Re2SiO5 bulk crystals. Two optical centers (Ce1 and Ce2) were observed for Re2SiO5:Ce3+ nanocrystals originating from cerium ions substituting 9- and 7-oxygen-coordinated cation sites. Preferential substitution of larger cation sites by cerium ions leads to higher photoluminescence intensity of Ce1 centers, however, Ce2 centers are the main centers for electron-hole recombination, so only Ce2 band is observed in X-ray luminescence spectra. The features of oxygen coordination of Ce1 and Ce2 centers and high content of oxygen vacancies in Re2SiO5:Ce3+ nanocrystals can provide preferential trapping of electrons near Ce2 centers, and therefore, the dominant role of Ce2 band in X-ray luminescence spectra. Full article
(This article belongs to the Special Issue Crystals, Films and Nanocomposite Scintillators)
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Open AccessArticle Modification of TiO2 Nanowire Arrays with Sn Doping as Photoanode for Highly Efficient Dye-Sensitized Solar Cells
Crystals 2019, 9(2), 113; https://doi.org/10.3390/cryst9020113
Received: 31 January 2019 / Revised: 15 February 2019 / Accepted: 16 February 2019 / Published: 21 February 2019
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Abstract
The dye-sensitized solar cell (DSSC) is one candidate among the third-generation solar cells. The performance of most DSSCs based on TiO2 photoanode was limited by the low electron mobility within TiO2. To produce a much higher power conversion efficiency, Sn-doped [...] Read more.
The dye-sensitized solar cell (DSSC) is one candidate among the third-generation solar cells. The performance of most DSSCs based on TiO2 photoanode was limited by the low electron mobility within TiO2. To produce a much higher power conversion efficiency, Sn-doped TiO2 nanowire arrays were successfully prepared using a simple hydrothermal process. It was found that Sn doping augments electron mobility well and raises the flat band potential to improve the performance of DSSCs. The power conversion efficiency (η) of a DSSC based on the reasonable Sn-doped TiO2, N719 dye, platinized counter electrode and iodide/triiodide electrolyte reaches 8.75%. Furthermore, with an anatase TiO2 light scattering layer, a DSSC based on the Sn-doped TiO2 NWAs exhibits a remarkable power conversion efficiency of 9.43%, which is especially useful in weak light conditions. Full article
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Open AccessFeature PaperReview The Effect of Pressure on Magnetic Properties of Prussian Blue Analogues
Crystals 2019, 9(2), 112; https://doi.org/10.3390/cryst9020112
Received: 8 January 2019 / Revised: 5 February 2019 / Accepted: 16 February 2019 / Published: 20 February 2019
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Abstract
We present the review of pressure effect on the crystal structure and magnetic properties of Cr(CN)6-based Prussian blue analogues (PBs). The lattice volume of the fcc crystal structure space group Fm3¯m in the Mn-Cr-CN-PBs linearly decreases for p [...] Read more.
We present the review of pressure effect on the crystal structure and magnetic properties of Cr(CN)6-based Prussian blue analogues (PBs). The lattice volume of the fcc crystal structure space group Fm 3 ¯ m in the Mn-Cr-CN-PBs linearly decreases for p ≤ 1.7 GPa, the change of lattice size levels off at 3.2 GPa, and above 4.2 GPa an amorphous-like structure appears. The crystal structure recovers after removal of pressure as high as 4.5 GPa. The effect of pressure on magnetic properties follows the non-monotonous pressure dependence of the crystal lattice. The amorphous like structure is accompanied with reduction of the Curie temperature (TC) to zero and a corresponding collapse of the ferrimagnetic moment at 10 GPa. The cell volume of Ni-Cr-CN-PBs decreases linearly and is isotropic in the range of 0–3.1 GPa. The Raman spectra can indicate a weak linkage isomerisation induced by pressure. The Curie temperature in Mn2+-CrIII-PBs and Cr2+-CrIII-PBs with dominant antiferromagnetic super-exchange interaction increases with pressure in comparison with decrease of TC in Ni2+-CrIII-PBs and Co2+-CrIII-PBs ferromagnets. TC increases with increasing pressure for ferrimagnetic systems due to the strengthening of magnetic interaction because pressure, which enlarges the monoelectronic overlap integral S and energy gap ∆ between the mixed molecular orbitals. The reduction of bonding angles between magnetic ions connected by the CN group leads to a small decrease of magnetic coupling. Such a reduction can be expected on both compounds with ferromagnetic and ferrimagnetic ordering. In the second case this effect is masked by the increase of coupling caused by the enlarged overlap between magnetic orbitals. In the case of mixed ferro–ferromagnetic systems, pressure affects μ(T) by a different method in Mn2+–N≡C–CrIII subsystem and CrIII–C≡N–Ni2+ subsystem, and as a consequence Tcomp decreases when the pressure is applied. The pressure changes magnetization processes in both systems, but we expect that spontaneous magnetization is not affected in Mn2+-CrIII-PBs, Ni2+-CrIII-PBs, and Co2+-CrIII-PBs. Pressure-induced magnetic hardening is attributed to a change in magneto-crystalline anisotropy induced by pressure. The applied pressure reduces saturated magnetization of Cr2+-CrIII-PBs. The applied pressure p = 0.84 GPa induces high spin–low spin transition of cca 4.5% of high spin Cr2+. The pressure effect on magnetic properties of PBs nano powders and core–shell heterostructures follows tendencies known from bulk parent PBs. Full article
(This article belongs to the Special Issue Molecular Magnets) Printed Edition available
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Open AccessArticle A Fast-Response and Helicity-Dependent Lens Enabled by Micro-Patterned Dual-Frequency Liquid Crystals
Crystals 2019, 9(2), 111; https://doi.org/10.3390/cryst9020111
Received: 7 January 2019 / Revised: 6 February 2019 / Accepted: 16 February 2019 / Published: 20 February 2019
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Abstract
Liquid crystals are excellent candidates for tunable optical elements due to their large birefringence and continuous tunability by external fields. A dual-frequency liquid crystal lens integrated with Pancharatnam–Berry phase was fabricated via a dynamic photo-patterning technique. The proposed lens exhibited distinctive polarization-dependent characteristics [...] Read more.
Liquid crystals are excellent candidates for tunable optical elements due to their large birefringence and continuous tunability by external fields. A dual-frequency liquid crystal lens integrated with Pancharatnam–Berry phase was fabricated via a dynamic photo-patterning technique. The proposed lens exhibited distinctive polarization-dependent characteristics and ultra-high efficiency rates of up to 95%. Via merely alternating the frequency of the applied electric field, the switching time between unfocused and focused states was measured in submilliseconds. This work supplies a new strategy for fast-response, high-efficiency and helicity-dependent lens with merits of easy fabrication and low power consumption. Full article
(This article belongs to the Special Issue Liquid Crystal Optics and Physics: Recent Advances and Prospects)
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Open AccessArticle Substituent Effects in the Crystal Packing of Derivatives of 4′-Phenyl-2,2′:6′,2″-Terpyridine
Crystals 2019, 9(2), 110; https://doi.org/10.3390/cryst9020110
Received: 4 February 2019 / Revised: 12 February 2019 / Accepted: 17 February 2019 / Published: 20 February 2019
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Abstract
We report the preparation of a series of new 4′-substituted 2,2′:6′,2″-terpyridines: 4′-(3,5-dimethylphenyl)-2,2′:6′,2″-terpyridine (2), 4′-(3-fluoro-5-methylphenyl)-2,2′:6′,2″-terpyridine (3), 4′-(3,5-difluorophenyl)-2,2′:6′,2″-terpyridine (4), and 4′-(3,5- bis(trifluoromethyl)phenyl)-2,2′:6′,2″-terpyridine (5). The compounds have been characterized by mass spectrometry, solid-state IR spectroscopy and solution NMR [...] Read more.
We report the preparation of a series of new 4′-substituted 2,2′:6′,2″-terpyridines: 4′-(3,5-dimethylphenyl)-2,2′:6′,2″-terpyridine (2), 4′-(3-fluoro-5-methylphenyl)-2,2′:6′,2″-terpyridine (3), 4′-(3,5-difluorophenyl)-2,2′:6′,2″-terpyridine (4), and 4′-(3,5- bis(trifluoromethyl)phenyl)-2,2′:6′,2″-terpyridine (5). The compounds have been characterized by mass spectrometry, solid-state IR spectroscopy and solution NMR and absorption spectroscopies. The single-crystal X-ray diffraction structures of 3, 5 and 6·EtOH (6 = 4′-(3,5-bis(tert-butyl)phenyl)-2,2′:6′,2″-terpyridine) have been elucidated. The molecular structures of the compounds are unexceptional. Since 3 and 5 crystallize without lattice solvent, we are able to understand the influence of introducing substituents in the 4′-phenyl ring and compare the packing in the structures with that of the previously reported 4′-phenyl-2,2′:6′,2″-terpyridine (1). On going from 1 to 3, face-to-face π-stacking of pairs of 3-fluoro-5-methylphenyl rings contributes to a change in packing from a herringbone assembly in 1 with no ring π-stacking to a layer-like packing. The latter arises through a combination of π-stacking of aromatic rings and N…H–C hydrogen bonding. On going from 3 to 5, N…H–C and F…H–C hydrogen-bonding is dominant, supplemented by π-stacking interactions between pairs of pyridine rings. A comparison of the packing of molecules of 6 with that in 1, 3 and 5 is difficult because of the incorporation of solvent in 6·EtOH. Full article
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Open AccessArticle Structure and Properties of 1,3-Phenylenediboronic Acid: Combined Experimental and Theoretical Investigations
Crystals 2019, 9(2), 109; https://doi.org/10.3390/cryst9020109
Received: 16 January 2019 / Revised: 14 February 2019 / Accepted: 15 February 2019 / Published: 19 February 2019
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Abstract
The structure and properties of 1,3-phenylenediboronic acid are reported. Molecular and crystal structures were determined by single crystal as well as by powder X-ray diffraction methods. Acidity constant, thermal behavior, and NMR characterization of the title compound were also investigated. In addition to [...] Read more.
The structure and properties of 1,3-phenylenediboronic acid are reported. Molecular and crystal structures were determined by single crystal as well as by powder X-ray diffraction methods. Acidity constant, thermal behavior, and NMR characterization of the title compound were also investigated. In addition to the experimental data, calculations of rotational barrier and intermolecular interaction energies were performed. The compound reveals a two-step acid–base equilibrium with different pKa values. TGA and DSC measurements show a typical dehydration reaction with formation of boroxine. In crystals, hydrogen-bonded dimers with syn-anti conformation of hydroxyl groups form large numbers of ribbon motifs. The 2D potential energy surface scan of rotation of two boronic groups with respect to phenyl ring reveals that the rotation barrier is close to 37 kJ⋅mol−1, which is higher than the double value for the rotation of the boronic group in phenylboronic acid. This effect was ascribed to intermolecular interaction with C–H hydrogen atom located between boronic groups. Furthermore, the molecules in the crystal lattice adopt a less stable molecular conformation most likely resulting from intermolecular forces. These were further investigated by periodic DFT calculations supported by an estimation of dimer interaction energy, and also by topological analysis of electron density in the framework of AIM theory. Full article
(This article belongs to the Special Issue Novel Hydrogen-bonded Materials with Significant Physical Properties)
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Open AccessArticle Preparation, Thermal, and Physical Properties of Perovskite-Type (C3H7NH3)2CdCl4 Crystals
Crystals 2019, 9(2), 108; https://doi.org/10.3390/cryst9020108
Received: 14 December 2018 / Revised: 12 February 2019 / Accepted: 14 February 2019 / Published: 19 February 2019
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Abstract
To investigate the thermal and physical properties of perovskite-type (C3H7NH3)2CdCl4, its temperature-dependent chemical shifts and spin–lattice relaxation times are measured using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), magic angle spinning nuclear magnetic [...] Read more.
To investigate the thermal and physical properties of perovskite-type (C3H7NH3)2CdCl4, its temperature-dependent chemical shifts and spin–lattice relaxation times are measured using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), magic angle spinning nuclear magnetic resonance (MAS NMR), and static NMR methods. Above 300 K, two phase transitions are observed at 398 K and 538 K. Each proton and carbon in the (C3H7NH3) cation is distinguished in the MAS NMR results. The environments around 1H, 13C, and 14N do not change with temperature according to the NMR spectra. In contrast, the resonance frequency of 113Cd in the CdCl6 octahedra decreases with increasing temperature, indicating an environmental change. The uniaxial rotations for 1H and 13C have high mobility at both high and low temperatures, and these are related to the phase transitions. In addition, the molecular motion of 113Cd in the anion becomes activated upon raising the temperature. Full article
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Open AccessArticle Crystal Structure of a Putative Modulator of Gyrase (TldE) from Thermococcus kodakarensis
Crystals 2019, 9(2), 107; https://doi.org/10.3390/cryst9020107
Received: 15 January 2019 / Revised: 11 February 2019 / Accepted: 15 February 2019 / Published: 19 February 2019
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Abstract
TldD and TldE proteins interact and form a complex to degrade unfolded peptides. The gene Tk0499 from Thermococcus kodakarensis encoded a putative modulator of gyrase (TkTldE). Although TldE genes were common in bacteria and archaea, the structural basis on the evolution [...] Read more.
TldD and TldE proteins interact and form a complex to degrade unfolded peptides. The gene Tk0499 from Thermococcus kodakarensis encoded a putative modulator of gyrase (TkTldE). Although TldE genes were common in bacteria and archaea, the structural basis on the evolution of proteins remained largely unknown. Here, the three-dimensional structure of TkTldE was determined by X-ray diffraction. Crystals were acquired by the sitting-drop vapor-diffusion method. X-ray diffraction data from crystals were collected at 2.35 Å. The space group and unit-cell parameters suggested that there were two molecules in the asymmetric unit. Our results showed that TkTldE forms a homodimer, which contained anti-parallel β-strands and a pair of α-helices. Comparison of the structures of TldE and TldD showed that despite their high sequence similarity, TldE lacked the conserved HExxxH and GxC motif in which two His and a Cys residues bound a metal ion. Taken together, these results provided insight into the structural information of this class of TldE/TldD. Full article
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Open AccessReview Choosing the Method of Crystallization to Obtain Optimal Results
Crystals 2019, 9(2), 106; https://doi.org/10.3390/cryst9020106
Received: 21 January 2019 / Revised: 11 February 2019 / Accepted: 16 February 2019 / Published: 19 February 2019
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Abstract
Anyone who has ever attempted to crystallise a protein or other biological macromolecule has encountered at least one, if not all of the following scenarios: No crystals at all, tiny low quality crystals; phase separation; amorphous precipitate and the most frustrating; large, beautiful [...] Read more.
Anyone who has ever attempted to crystallise a protein or other biological macromolecule has encountered at least one, if not all of the following scenarios: No crystals at all, tiny low quality crystals; phase separation; amorphous precipitate and the most frustrating; large, beautiful crystals that do not diffract at all. In this paper we review a number of simple ways to overcome such problems, which have worked well in our hands and in other laboratories. It brings together information that has been dispersed in various publications and lectures over the years and includes further information that has not been previously published. Full article
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Open AccessArticle Identification of Unentangled–Entangled Border in the Luttinger Liquid Phase
Crystals 2019, 9(2), 105; https://doi.org/10.3390/cryst9020105
Received: 8 January 2019 / Revised: 6 February 2019 / Accepted: 14 February 2019 / Published: 18 February 2019
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Abstract
Quantum discord and entanglement are both criteria for distinguishing quantum correlations in a quantum system. We studied the effect of the transverse magnetic field on the quantum discord of the one-dimensional spin-1/2 XX model. This study focused on the pair of spins at [...] Read more.
Quantum discord and entanglement are both criteria for distinguishing quantum correlations in a quantum system. We studied the effect of the transverse magnetic field on the quantum discord of the one-dimensional spin-1/2 XX model. This study focused on the pair of spins at different distances. We show that quantum discord is finite for all studied spin pairs in the Luttinger liquid phase. In addition, relying on our calculations, we show that the derivatives of quantum discord can be used to identify the border between entangled and separable regions in the Luttinger liquid phase. Full article
(This article belongs to the Special Issue Magnetic Field-induced Phase Transition)
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Open AccessArticle Insight into Physical and Thermodynamic Properties of X3Ir (X = Ti, V, Cr, Nb and Mo) Compounds Influenced by Refractory Elements: A First-Principles Calculation
Crystals 2019, 9(2), 104; https://doi.org/10.3390/cryst9020104
Received: 21 January 2019 / Revised: 5 February 2019 / Accepted: 14 February 2019 / Published: 18 February 2019
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Abstract
The effects of refractory metals on physical and thermodynamic properties of X3Ir (X = Ti, V, Cr, Nb and Mo) compounds were investigated using local density approximation (LDA) and generalized gradient approximation (GGA) methods within the first-principles calculations based on density [...] Read more.
The effects of refractory metals on physical and thermodynamic properties of X3Ir (X = Ti, V, Cr, Nb and Mo) compounds were investigated using local density approximation (LDA) and generalized gradient approximation (GGA) methods within the first-principles calculations based on density functional theory. The optimized lattice parameters were both in good compliance with the experimental parameters. The GGA method could achieve an improved structural optimization compared to the LDA method, and thus was utilized to predict the elastic, thermodynamic and electronic properties of X3Ir (X = Ti, V, Cr, Nb and Mo) compounds. The calculated mechanical properties (i.e., elastic constants, elastic moduli and elastic anisotropic behaviors) were rationalized and discussed in these intermetallics. For instance, the derived bulk moduli exhibited the sequence of Ti3Ir < Nb3Ir < V3Ir < Cr3Ir < Mo3Ir. This behavior was discussed in terms of the volume of unit cell and electron density. Furthermore, Debye temperatures were derived and were found to show good consistency with the experimental values, indicating the precision of our calculations. Finally, the electronic structures were analyzed to explain the ductile essences in the iridium compounds. Full article
(This article belongs to the Special Issue First-Principles Prediction of Structures and Properties in Crystals)
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Open AccessArticle Design of Polarization Splitter via Liquid and Ti Infiltrated Photonic Crystal Fiber
Crystals 2019, 9(2), 103; https://doi.org/10.3390/cryst9020103
Received: 31 January 2019 / Revised: 14 February 2019 / Accepted: 15 February 2019 / Published: 18 February 2019
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Abstract
We propose a new polarization splitter (PS) based on Ti and liquid infiltrated photonic crystal fiber (PCF) with high birefringence. Impacts of parameters such as shape and size of the air holes in the cladding and filling material are investigated by using a [...] Read more.
We propose a new polarization splitter (PS) based on Ti and liquid infiltrated photonic crystal fiber (PCF) with high birefringence. Impacts of parameters such as shape and size of the air holes in the cladding and filling material are investigated by using a vector beam propagation method. The results indicate that the PS offers an ultra-short length of 83.9 μm, a high extinction ratio of −44.05 dB, and a coupling loss of 0.0068 dB and at 1.55 μm. Moreover, an extinction ratio higher than −10 dB is achieved a bandwidth of 32.1 nm. Full article
(This article belongs to the Special Issue Sonic and Photonic Crystals)
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Open AccessArticle Effect of Side Surface Orientation on the Mechanical Properties of Silicon Nanowires: A Molecular Dynamics Study
Crystals 2019, 9(2), 102; https://doi.org/10.3390/cryst9020102
Received: 20 January 2019 / Revised: 11 February 2019 / Accepted: 12 February 2019 / Published: 18 February 2019
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We investigated the mechanical properties of <100>-oriented square cross-sectional silicon nanowires under tension and compression, with a focus on the effect of side surface orientation. Two types of silicon nanowires (i.e., nanowires with four {100} side surfaces and those with four {110} side [...] Read more.
We investigated the mechanical properties of <100>-oriented square cross-sectional silicon nanowires under tension and compression, with a focus on the effect of side surface orientation. Two types of silicon nanowires (i.e., nanowires with four {100} side surfaces and those with four {110} side surfaces) were simulated by molecular dynamics simulations at a temperature of 300 K. The deformation mechanism exhibited no dependence on the side surface orientation, while the tensile strength and compressive strength did. Brittle cleavage was observed under tension, whereas dislocation nucleation was witnessed under compression. Silicon nanowires with {100} side surfaces had a lower tensile strength but higher compressive strength. The effect of side surface orientation became stronger as the nanowire width decreased. The obtained results may provide some insight into the design of silicon-based nano-devices. Full article
(This article belongs to the Section Crystalline Materials)
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Open AccessArticle A New Half-Salamo-Based Homo-Trinuclear Nickel(II) Complex: Crystal Structure, Hirshfeld Surface Analysis, and Fluorescence Properties
Crystals 2019, 9(2), 101; https://doi.org/10.3390/cryst9020101
Received: 10 January 2019 / Revised: 3 February 2019 / Accepted: 15 February 2019 / Published: 18 February 2019
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Abstract
A new homo-trinuclear Ni(II) half-salamo-based complex [Ni3(L)2(μ-OAc)2(OAc)2(CH3OH)2]·2CH3OH was synthesized via the reaction of a tridentate ligand HL (2-[O-(1-ethyloxyamide)]oxime-4-bromophenol) and Ni(OAc)2·4H2O, and [...] Read more.
A new homo-trinuclear Ni(II) half-salamo-based complex [Ni3(L)2(μ-OAc)2(OAc)2(CH3OH)2]·2CH3OH was synthesized via the reaction of a tridentate ligand HL (2-[O-(1-ethyloxyamide)]oxime-4-bromophenol) and Ni(OAc)2·4H2O, and characterized using elemental analyses, IR spectra, UV-Vis absorption spectra, X-ray crystallography, and Hirshfeld analysis. Interestingly, single-crystal X-ray analysis showed that the two acetate molecules were bonded simultaneously with the Ni(II) atoms by mono-dentate chelating and bidentate bridging coordination modes, respectively, and the resulting hexa-coordinate geometries were ultimately formed. Furthermore, the Hirshfeld analysis of the complex was studied. Compared with HL, the complex fluorescence intensity was significantly lowered, indicating that the Ni(II) ions have fluorescence quenching characteristics. Full article
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Open AccessArticle Effect of C on the Martensitic Transformation in Fe-C Alloys in the Presence of Pre-Existing Defects: A Molecular Dynamics Study
Crystals 2019, 9(2), 99; https://doi.org/10.3390/cryst9020099
Received: 12 December 2018 / Revised: 31 January 2019 / Accepted: 5 February 2019 / Published: 15 February 2019
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Abstract
Molecular dynamics simulations are used to investigate the atomic effects of carbon (C) addition in Fe on the martensitic phase transformation in the presence of pre-existing defects such as stacking faults and twin boundaries. The pre-existing defect structures in Fe-C alloys have the [...] Read more.
Molecular dynamics simulations are used to investigate the atomic effects of carbon (C) addition in Fe on the martensitic phase transformation in the presence of pre-existing defects such as stacking faults and twin boundaries. The pre-existing defect structures in Fe-C alloys have the same effect on the atomistic mechanisms of martensitic transformation as in pure Fe. However, C addition decreases the martensitic transformation temperature. This effect is captured by characterizing three parameters at the atomic level: atomic shear stresses, atomic energy, and total energy as a function of temperature for face-centered-cubic (fcc) and body-centered-cubic (bcc) phases. The thermodynamic effect of fcc phase stabilization by C addition is revealed by the atomic energy at a particular temperature and total energy as a function of temperature. The barrier for fcc-to-bcc transformation is revealed by analysis of atomic shear stresses. The analysis indicates that addition of C increases the atomic shear stresses for atomic displacements during martensitic transformation, which in turn decreases the martensitic transformation temperature. Full article
(This article belongs to the Special Issue Microstructures and Properties of Martensitic Materials)
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Open AccessArticle Element Segregation and Electrical Properties of PMN-32PT Grown Using the Bridgman Method
Crystals 2019, 9(2), 98; https://doi.org/10.3390/cryst9020098
Received: 5 January 2019 / Revised: 29 January 2019 / Accepted: 13 February 2019 / Published: 15 February 2019
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Abstract
A single crystal with nominal composition Pb(Mg1/3Nb2/3)O3-32PbTiO3 (PMN-32PT) was grown by the Bridgman technique. Crystal orientation was determined using the rotating orientation X-ray diffraction (RO-XRD). Element distribution was measured along different directions using inductively coupled plasma-mass [...] Read more.
A single crystal with nominal composition Pb(Mg1/3Nb2/3)O3-32PbTiO3 (PMN-32PT) was grown by the Bridgman technique. Crystal orientation was determined using the rotating orientation X-ray diffraction (RO-XRD). Element distribution was measured along different directions using inductively coupled plasma-mass spectrometry (ICP-MS). The effect of the element segregation along axial and radial directions on the electrical properties of the PMN-32PT crystal was investigated. It is indicated that the electrical properties of the samples along the axial direction were strongly dependent on the PT (PbTiO3) content. With the increase of the PT content, the piezoelectric coefficient and remnant polarization were improved. Differently, the electrical properties of the samples along the radial direction were mainly determined by the ratio of the Nb and Mg. The reasons for the element segregation and electrical properties varied with the composition were discussed. Full article
(This article belongs to the Special Issue Synthesis and Characterization of Ferroelectrics)
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Open AccessReview Crystallochemical Design of Huntite-Family Compounds
Crystals 2019, 9(2), 100; https://doi.org/10.3390/cryst9020100
Received: 18 December 2018 / Revised: 9 February 2019 / Accepted: 12 February 2019 / Published: 15 February 2019
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Abstract
Huntite-family nominally-pure and activated/co-activated LnM3(BO3)4 (Ln = La–Lu, Y; M = Al, Fe, Cr, Ga, Sc) compounds and their-based solid solutions are promising materials for lasers, nonlinear optics, spintronics, and photonics, which are characterized by multifunctional properties [...] Read more.
Huntite-family nominally-pure and activated/co-activated LnM3(BO3)4 (Ln = La–Lu, Y; M = Al, Fe, Cr, Ga, Sc) compounds and their-based solid solutions are promising materials for lasers, nonlinear optics, spintronics, and photonics, which are characterized by multifunctional properties depending on a composition and crystal structure. The purpose of the work is to establish stability regions for the rare-earth orthoborates in crystallochemical coordinates (sizes of Ln and M ions) based on their real compositions and space symmetry depending on thermodynamic, kinetic, and crystallochemical factors. The use of diffraction structural techniques to study single crystals with a detailed analysis of diffraction patterns, refinement of crystallographic site occupancies (real composition), and determination of structure–composition correlations is the most efficient and effective option to achieve the purpose. This approach is applied and shown primarily for the rare-earth scandium borates having interesting structural features compared with the other orthoborates. Visualization of structures allowed to establish features of formation of phases with different compositions, to classify and systematize huntite-family compounds using crystallochemical concepts (structure and superstructure, ordering and disordering, isostructural and isotype compounds) and phenomena (isomorphism, morphotropism, polymorphism, polytypism). Particular attention is paid to methods and conditions for crystal growth, affecting a crystal real composition and symmetry. A critical analysis of literature data made it possible to formulate unsolved problems in materials science of rare-earth orthoborates, mainly scandium borates, which are distinguished by an ability to form internal and substitutional (Ln and Sc atoms), unlimited and limited solid solutions depending on the geometric factor. Full article
(This article belongs to the Special Issue Crystal Growth of Multifunctional Borates and Related Materials)
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Open AccessArticle Threefold Spiral Structure Constructed by 1D Chains of [[M(NCS)2(bpa)2]·biphenyl]n (M = Fe, Co; bpa = 1,2-bis(4-pyridyl)ethane)
Crystals 2019, 9(2), 97; https://doi.org/10.3390/cryst9020097
Received: 27 December 2018 / Revised: 12 February 2019 / Accepted: 12 February 2019 / Published: 14 February 2019
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Abstract
Assembled complexes [[M(NCS)2(bpa)2]·biphenyl]n (M = Fe, Co; bpa = 1,2-bis(4-pyridyl)ethane) have been synthesized because [Fe(NCBH3)2(bpa)2·biphenyl]n has a novel threefold spiral structure and shows stepwise spin-crossover phenomenon. We attempted to obtain spiral [...] Read more.
Assembled complexes [[M(NCS)2(bpa)2]·biphenyl]n (M = Fe, Co; bpa = 1,2-bis(4-pyridyl)ethane) have been synthesized because [Fe(NCBH3)2(bpa)2·biphenyl]n has a novel threefold spiral structure and shows stepwise spin-crossover phenomenon. We attempted to obtain spiral structures for [[Fe(NCS)2(bpa)2]·biphenyl]n and [[Co(NCS)2(bpa)2]·biphenyl]n using a one-step diffusion method, while the reported spiral structure of [[Fe(NCBH3)2(bpa)2]·biphenyl]n was obtained by diffusion method after synthesizing Fe(II)-pyridine complex. X-ray structural analysis revealed that [[Fe(NCS)2(bpa)2]·biphenyl]n and [[Co(NCS)2(bpa)2]·biphenyl]n had a chiral propeller structure of pyridines around the central metal, and they had a novel spiral structure and chiral space group P3121 without the presence of chiral auxiliaries. It was shown that the host 1D chain, having a chiral propeller structure of pyridines around the central metal along with its concerted interaction with an atropisomer of biphenyl, made a threefold spiral structure. Full article
(This article belongs to the Special Issue Synthesis and Applications of New Spin Crossover Compounds)
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Open AccessArticle Construction and Optimization of Through-Hole LED Models for Use in Designing Traffic Signboards
Crystals 2019, 9(2), 96; https://doi.org/10.3390/cryst9020096
Received: 30 November 2018 / Revised: 2 February 2019 / Accepted: 12 February 2019 / Published: 14 February 2019
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Abstract
A modeling procedure was proposed for the through-hole LEDs commonly used in traffic signs. The measurements from a sample batch of LEDs were performed at several midfield distances to provide a set of representative angular intensity distributions as the target pattern in the [...] Read more.
A modeling procedure was proposed for the through-hole LEDs commonly used in traffic signs. The measurements from a sample batch of LEDs were performed at several midfield distances to provide a set of representative angular intensity distributions as the target pattern in the modeling process. The flat outer dimensions of the LED were accurately measured while the curvature and refractive index of the packaging dome were roughly estimated. These physical parameters were used to build a preliminary LED model in the Monte Carlo simulation software. The simulated angular intensity distribution at each distance was generated by tracing 20,000,000 rays. The normalized cross correlation (NCC) between the measured and simulated data was calculated to represent the resemblance of the model to the real LED. The roughly estimated parameters were then varied within their physical limits to optimize the NCC value. The possibilities of two parameters having interactions were also considered. The final model has all NCCs above 98.8% between the target and simulated patterns. Full article
(This article belongs to the Special Issue Advanced LED Solid-state Lighting Optics)
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Open AccessReview Recent Advances on Carrier and Exciton Self-Trapping in Strontium Titanate: Understanding the Luminescence Emissions
Crystals 2019, 9(2), 95; https://doi.org/10.3390/cryst9020095
Received: 29 December 2018 / Revised: 4 February 2019 / Accepted: 11 February 2019 / Published: 13 February 2019
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Abstract
An up-to-date review on recent results for self-trapping of free electrons and holes, as well as excitons, in strontium titanate (STO), which gives rise to small polarons and self-trapped excitons (STEs) is presented. Special attention is paid to the role of carrier and [...] Read more.
An up-to-date review on recent results for self-trapping of free electrons and holes, as well as excitons, in strontium titanate (STO), which gives rise to small polarons and self-trapped excitons (STEs) is presented. Special attention is paid to the role of carrier and exciton self-trapping on the luminescence emissions under a variety of excitation sources with special emphasis on experiments with laser pulses and energetic ion-beams. In spite of the extensive research effort, a definitive identification of such localized states, as well as a suitable understanding of their operative light emission mechanisms, has remained lacking or controversial. However, promising advances have been recently achieved and are the objective of the present review. In particular, significant theoretical advances in the understanding of electron and hole self-trapping are discussed. Also, relevant experimental advances in the kinetics of light emission associated with electron-hole recombination have been obtained through time-resolved experiments using picosecond (ps) laser pulses. The luminescence emission mechanisms and the light decay processes from the self-trapped excitons are also reviewed. Recent results suggest that the blue emission at 2.8 eV, often associated with oxygen vacancies, is related to a transition from unbound conduction levels to the ground singlet state of the STE. The stabilization of small electron polarons by oxygen vacancies and its connection with luminescence emission are discussed in detail. Through ion-beam irradiation experiments, it has recently been established that the electrons associated with the vacancy constitute electron polaron states (Ti3+) trapped in the close vicinity of the empty oxygen sites. These experimental results have allowed for the optical identification of the oxygen vacancy center through a red luminescence emission centered at 2.0 eV. Ab-initio calculations have provided strong support for those experimental findings. Finally, the use of Cr-doped STO has offered a way to monitor the interplay between the chromium centers and oxygen vacancies as trapping sites for the electron and hole partners resulting from the electronic excitation. Full article
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Open AccessArticle The Mechanism of High-Strength Quenching-Partitioning-Tempering Martensitic Steel at Elevated Temperatures
Crystals 2019, 9(2), 94; https://doi.org/10.3390/cryst9020094
Received: 11 December 2018 / Revised: 21 January 2019 / Accepted: 1 February 2019 / Published: 13 February 2019
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Abstract
High-strength medium-carbon martensitic steel was heat treated through a quenching-partitioning-tempering (Q-P-T) treatment. Both the mechanism for improved ductility and the high temperature stability of austenite were investigated. The Q-P-T martensitic steel showed good products of strength and elongation (PSE) at various deformation temperatures [...] Read more.
High-strength medium-carbon martensitic steel was heat treated through a quenching-partitioning-tempering (Q-P-T) treatment. Both the mechanism for improved ductility and the high temperature stability of austenite were investigated. The Q-P-T martensitic steel showed good products of strength and elongation (PSE) at various deformation temperatures ranging within 25–350 °C. The optimum PSE value (>57,738 MPa%) was achieved at 200 °C. The microstructure of the Q-P-T steel is constituted of laths martensite with dislocations, retained austenite located within lath martensite and small niobium carbides (NbC), and/or transitional ε-carbides that precipitated in the lath martensite. The good ductility can be mainly attributed to the laminar-like austenite that remained within the lath-martensite. The austenite can effectively enhance ductility through the effect of dislocation absorption by the retained austenite and through transformation-induced plasticity. The relationship between the microstructures and mechanical properties was investigated at high deformation temperatures. Full article
(This article belongs to the Special Issue Microstructures and Properties of Martensitic Materials)
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Open AccessArticle Thermodynamics and Magnetic Excitations in Quantum Spin Trimers: Applications for the Understanding of Molecular Magnets
Crystals 2019, 9(2), 93; https://doi.org/10.3390/cryst9020093
Received: 21 January 2019 / Revised: 3 February 2019 / Accepted: 4 February 2019 / Published: 12 February 2019
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Abstract
Molecular magnets provide a playground of interesting phenomena and interactions that have direct applications for quantum computation and magnetic systems. A general understanding of the underlying geometries for molecular magnets therefore generates a consistent foundation for which further analysis and understanding can be [...] Read more.
Molecular magnets provide a playground of interesting phenomena and interactions that have direct applications for quantum computation and magnetic systems. A general understanding of the underlying geometries for molecular magnets therefore generates a consistent foundation for which further analysis and understanding can be established. Using a Heisenberg spin-spin exchange Hamiltonian, we investigate the evolution of magnetic excitations and thermodynamics of quantum spin isosceles trimers (two sides J and one side α J ) with increasing spin. For the thermodynamics, we produce exact general solutions for the energy eigenstates and spin decomposition, which can be used to determine the heat capacity and magnetic susceptibility quickly. We show how the thermodynamic properties change with α coupling parameters and how the underlying ground state governs the Schottky anomaly. Furthermore, we investigate the microscopic excitations by examining the inelastic neutron scattering excitations and structure factors. Here, we illustrate how the individual dimer subgeometry governs the ability for probing underlying excitations. Overall, we feel these calculations can help with the general analysis and characterization of molecular magnet systems. Full article
(This article belongs to the Special Issue Molecular Magnets) Printed Edition available
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Open AccessArticle A 1,6-Diphenylpyrene-Based, Photoluminescent Cyclophane Showing a Nematic Liquid-Crystalline Phase at Room Temperature
Crystals 2019, 9(2), 92; https://doi.org/10.3390/cryst9020092
Received: 21 January 2019 / Revised: 9 February 2019 / Accepted: 9 February 2019 / Published: 11 February 2019
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Abstract
Photoluminescent nematic liquid crystals have been an attractive research target for decades, because of their potential applications in optoelectrical devices. Integration of luminescent motifs into cyclic structures is a promising approach to induce low-ordered liquid-crystalline phases, even though relatively large and rigid luminophores [...] Read more.
Photoluminescent nematic liquid crystals have been an attractive research target for decades, because of their potential applications in optoelectrical devices. Integration of luminescent motifs into cyclic structures is a promising approach to induce low-ordered liquid-crystalline phases, even though relatively large and rigid luminophores are used as emitters. Here, we demonstrate a 1,6-diphenylpyrene-based, unsymmetric cyclophane showing a stable nematic phase at room temperature and exhibiting strong photoluminescence from the condensed state. The observed sky-blue photoluminescence was dominated by the emission species ascribed to assembled luminophores rather than monomers. Full article
(This article belongs to the Special Issue Synthesis and Properties of Light-emitting Liquid Crystals)
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Open AccessArticle Terbium Substituted Lanthanum Orthoniobate: Electrical and Structural Properties
Crystals 2019, 9(2), 91; https://doi.org/10.3390/cryst9020091
Received: 2 January 2019 / Revised: 5 February 2019 / Accepted: 6 February 2019 / Published: 11 February 2019
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Abstract
The results of electrical conductivity studies, structural measurements and thermogravimetric analysis of La1−xTbxNbO4+δ (x = 0.00, 0.05, 0.1, 0.15, 0.2, 0.3) are presented and discussed. The phase transition temperatures, measured by high-temperature x-ray diffraction, were 480 °C, 500 [...] Read more.
The results of electrical conductivity studies, structural measurements and thermogravimetric analysis of La1−xTbxNbO4+δ (x = 0.00, 0.05, 0.1, 0.15, 0.2, 0.3) are presented and discussed. The phase transition temperatures, measured by high-temperature x-ray diffraction, were 480 °C, 500 °C, and 530 °C for La0.9Tb0.1NbO4+δ, La0.8Tb0.2NbO4+δ, and La0.7Tb0.3NbO4+δ, respectively. The impedance spectroscopy results suggest mixed conductivity of oxygen ions and electron holes in dry conditions and protons in wet. The water uptake has been analyzed by the means of thermogravimetry revealing a small mass increase in the order of 0.002% upon hydration, which is similar to the one achieved for undoped lanthanum orthoniobate. Full article
(This article belongs to the Special Issue Ceramic Conductors)
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Open AccessArticle Very Low Nucleation Rates of Glucose Isomerase Crystals under Microgravity in the International Space Station
Crystals 2019, 9(2), 90; https://doi.org/10.3390/cryst9020090
Received: 28 December 2018 / Revised: 5 February 2019 / Accepted: 8 February 2019 / Published: 11 February 2019
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Abstract
In situ observation of the nucleation and growth of glucose isomerase (GI) crystals under microgravity was conducted using an optical microscope during the first flight of the Advanced Nano Step project undertaken in the International Space Station (ISS). Very low apparent nucleation rates [...] Read more.
In situ observation of the nucleation and growth of glucose isomerase (GI) crystals under microgravity was conducted using an optical microscope during the first flight of the Advanced Nano Step project undertaken in the International Space Station (ISS). Very low apparent nucleation rates (J’) of GI crystals in the solution and on the substrate of the growth container were confirmed compared with those on the ground. In particular, J’ of GI crystals in the solution were a few times lower than that on the substrate. The growth rates (R) of the {101} faces of GI crystals on the substrate and the apparent growth rates (R’) in the solution were measured. The very low nucleation rates allowed us to successfully measure R at a very high supersaturation region (up to ln(C/Ce) = 6), at which R cannot be measured on the ground. Full article
(This article belongs to the Special Issue Protein Crystallography)
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