Open AccessArticle
Vickers Hardness of Diamond and cBN Single Crystals: AFM Approach
Crystals 2017, 7(12), 369; doi:10.3390/cryst7120369 (registering DOI) -
Abstract
Atomic force microscopy in different operation modes (topography, derivative topography, and phase contrast) was used to obtain 3D images of Vickers indents on the surface of diamond and cBN single crystals with high spatial resolution. Confocal Raman spectroscopy and Kelvin probe force microscopy
[...] Read more.
Atomic force microscopy in different operation modes (topography, derivative topography, and phase contrast) was used to obtain 3D images of Vickers indents on the surface of diamond and cBN single crystals with high spatial resolution. Confocal Raman spectroscopy and Kelvin probe force microscopy were used to study the structure of the material in the indents. It was found that Vickers indents in diamond has no sharp and clear borders. However, the phase contrast operation mode of the AFM reveals a new viscoelastic phase in the indent in diamond. Raman spectroscopy and Kelvin probe force microscopy revealed that the new phase in the indent is disordered graphite, which was formed due to the pressure-induced phase transformation in the diamond during the hardness test. The projected contact area of the graphite layer in the indent allows us to measure the Vickers hardness of type-Ib synthetic diamond. In contrast to diamond, very high plasticity was observed for 0.5 N load indents on the (001) cBN single crystal face. Radial and ring cracks were absent, the shape of the indents was close to a square, and there were linear details in the indent, which looked like slip lines. The Vickers hardness of the (111) synthetic diamond and (111) and (001) cBN single crystals were determined using the AFM images and with account for the elastic deformation of the diamond Vickers indenter during the tests. Full article
Figures

Figure 1

Open AccessArticle
Phononic Crystal Made of Multilayered Ridges on a Substrate for Rayleigh Waves Manipulation
Crystals 2017, 7(12), 372; doi:10.3390/cryst7120372 (registering DOI) -
Abstract
We present a phononic crystal to achieve efficient manipulation of surface acoustic waves (SAW). The structure is made of finite phononic micro-ridges arranged periodically in a substrate surface. Each ridge is constructed by staking silicon and tungsten layers so that it behaves as
[...] Read more.
We present a phononic crystal to achieve efficient manipulation of surface acoustic waves (SAW). The structure is made of finite phononic micro-ridges arranged periodically in a substrate surface. Each ridge is constructed by staking silicon and tungsten layers so that it behaves as one-dimensional phononic crystal which exhibits band gaps for elastic waves. The band gap allows the existence of resonance modes where the elastic energy is either confined within units in the free end of the ridge or the ones in contact with the substrate. We show that SAW interaction with localized modes in the free surface of the ridge gives rise to sharp attenuation in the SAW transmission, while the modes confined within the ridge/substrate interface cause broad band attenuations of SAW. Furthermore, we demonstrate that the coupling between the two kinds of modes within the band gap gives high SAW transmission amplitude in the form of Fano-like peaks with high quality factor. The structure could provide an interesting solution for accurate SAW control for sensing applications, for instance. Full article
Figures

Figure 1

Open AccessArticle
Hydrophobic Calcium Carbonate for Cement Surface
Crystals 2017, 7(12), 371; doi:10.3390/cryst7120371 -
Abstract
This report describes a novel way to generate a highly effective hydrophobic cement surface via a carbonation route using sodium stearate. Carbonation reaction was carried out at different temperatures to investigate the hydrophobicity and morphology of the calcium carbonate formed with this process.
[...] Read more.
This report describes a novel way to generate a highly effective hydrophobic cement surface via a carbonation route using sodium stearate. Carbonation reaction was carried out at different temperatures to investigate the hydrophobicity and morphology of the calcium carbonate formed with this process. With increasing temperatures, the particles changed from irregular shapes to more uniform rod-like structures and then aggregated to form a plate-like formation. The contact angle against water was found to increase with increasing temperature; after 90 °C there was no further increase. The maximum contact angle of 129° was obtained at the temperature of 60 °C. It was also found that carbonation increased the micro hardness of the cement material. The micro hardness was found to be dependent on the morphology of the CaCO3 particles. The rod like structures which caused increased mineral filler produced a material with enhanced strength. The 13C cross polarization magic-angle spinning NMR spectra gave plausible explanation of the interaction of organic-inorganic moieties. Full article
Figures

Figure 1

Open AccessArticle
Synthesis, Crystal Structure, Gas Absorption, and Separation Properties of a Novel Complex Based on Pr and a Three-Connected Ligand
Crystals 2017, 7(12), 370; doi:10.3390/cryst7120370 -
Abstract
A novel Pr complex, constructed from a rigid three-connected H3TMTA and praseodymium(III) ion, has been synthesized in a mixed solvent system and characterized by X-ray single crystal diffraction, infrared spectroscopy, a thermogravimetric analysis, an element analysis, and powder X-ray diffraction, which
[...] Read more.
A novel Pr complex, constructed from a rigid three-connected H3TMTA and praseodymium(III) ion, has been synthesized in a mixed solvent system and characterized by X-ray single crystal diffraction, infrared spectroscopy, a thermogravimetric analysis, an element analysis, and powder X-ray diffraction, which reveals that complex 1 crystallizes in a three-dimensional porous framework. Moreover, the thermal stabilities and the fluorescent and gas adsorption and separation properties of complex 1 were investigated systematically. Full article
Figures

Figure 1

Open AccessArticle
Improvement in the Photorefractive Response Speed and Mechanism of Pure Congruent Lithium Niobate Crystals by Increasing the Polarization Current
Crystals 2017, 7(12), 368; doi:10.3390/cryst7120368 -
Abstract
A series of pure congruent lithium niobate (LiNbO3, CLN) crystals were grown and directly polarized under different electric currents in the growth furnace. Their holographic properties were investigated from the ultraviolet to the visible range. The response time shortened, whereas the
[...] Read more.
A series of pure congruent lithium niobate (LiNbO3, CLN) crystals were grown and directly polarized under different electric currents in the growth furnace. Their holographic properties were investigated from the ultraviolet to the visible range. The response time shortened, whereas the diffraction efficiency increased incrementally with the electric current. In particular, the response time of CLN polarized under 100 mA can be reduced by a factor of 10 with a still high saturation diffraction efficiency of about 40.8% at 351 nm. Moreover, its response speed improved by 60 times and 10 times for 473 and 532 nm laser, respectively. The light erasing behavior implies that at least two kinds of photorefractive centers exist in the crystals. Increasing the polarization current induces two pronounced UV absorption peaks and a wide visible absorption peak in CLN crystals. The diffusion effect dominates the photorefractive process and electrons are the dominant carriers. The possible mechanism for the fast photorefractive response is discussed. Increasing the polarization electric current is an effective method to improve the photorefractive response of LN crystal. Full article
Figures

Figure 1

Open AccessArticle
Chalcogenide Quaternary Cu2FeSnS4 Nanocrystals for Solar Cells: Explosive Character of Mechanochemical Synthesis and Environmental Challenge
Crystals 2017, 7(12), 367; doi:10.3390/cryst7120367 -
Abstract
In this study we demonstrate the synthesis of quaternary semiconductor nanocrystals of stannite Cu2FeSnS4/rhodostannite Cu2FeSn3S8 (CFTS) via mechanochemical route using Cu, Fe, Sn and S elements as precursors in one-pot experiments. Methods of X-ray
[...] Read more.
In this study we demonstrate the synthesis of quaternary semiconductor nanocrystals of stannite Cu2FeSnS4/rhodostannite Cu2FeSn3S8 (CFTS) via mechanochemical route using Cu, Fe, Sn and S elements as precursors in one-pot experiments. Methods of X-ray diffraction (XRD), nitrogen adsorption, high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) were applied to characterize properties of the unique nanostructures. Mechanochemical route of synthesis induced new phenomena like explosive character of reaction, where three stages could be identified and the formation of nanostructures 5–10 nm in size. By using XPS method, Cu(I), Fe(II), Sn(IV) and S(-II) species were identified on the surface of CFTS. The value of optical band gap 1.27 eV is optimal for semiconductors applicable as absorbers in solar cells. The significant photocatalytic activity of the CFTS nanocrystals was also evidenced. The obtained results confirm the excellent properties of the quaternary semiconductor nanocrystals synthesized from earth-abundant elements. Full article
Figures

Figure 1

Open AccessArticle
Structural Characterization of Febuxostat/l-Pyroglutamic Acid Cocrystal Using Solid-State 13C-NMR and Investigational Study of Its Water Solubility
Crystals 2017, 7(12), 365; doi:10.3390/cryst7120365 -
Abstract
Febuxostat (FB) is a poorly water-soluble drug that belongs to BCS class II. The drug is employed for the treatment of inflammatory disease arthritis urica (gout), and the free base, FB form-A, is most preferred for drug formulation. In order to achieve a
[...] Read more.
Febuxostat (FB) is a poorly water-soluble drug that belongs to BCS class II. The drug is employed for the treatment of inflammatory disease arthritis urica (gout), and the free base, FB form-A, is most preferred for drug formulation. In order to achieve a goal of improving the water solubility of FB form-A, this study was carried out using the cocrystallization technique called the liquid-assisted grinding method to produce FB cocrystals. Here, five amino acids containing amine (NH), oxygen (O), and hydroxyl (OH) functional groups, and possessing difference of pKa less than 3 with FB, were selected as coformers. Then, solvents including methanol, ethanol, isopropyl alcohol, n-hexane, dichloromethane, and acetone were used for the cocrystal screening. As a result, a cocrystal was obtained when acetone and l-pyroglutamic acid (PG) of 0.5 eq. were employed as solvent and coformer, respectively. The ratio of 2:1, which is the ratio of FB to PG within FB-PG cocrystal, was predicted by means of solid-state CP/MAS 13C-NMR, solution-state NMR (1H, 13C, and 2D) and FT-IR. Moreover, Powder X-ray Diffraction (PXRD), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA) were used to investigate the characteristics of FB-PG cocrystal. In addition, comparative solubility tests between FB-PG cocrystal and FB form-A were conducted in deionized water and under simulated gastrointestinal pH (1.2, 4, and 6.8) conditions. The result revealed that FB-PG cocrystal has a solubility of four-fold higher than FB form-A in deionized water and two-fold and five-fold greater than FB form-A at simulated gastrointestinal pH 1.2 and pH 4, respectively. Besides, solubilities of FB-PG cocrystal and FB form-A at pH 6.8 were similar to the results measured in deionized water. Therefore, it is postulated that FB-PG cocrystal has a potential overcoming the limitations related to the low aqueous solubility of FB form-A. Accordingly, FB-PG cocrystal is suggested as an alternative active pharmaceutical ingredient of the currently used FB form-A. Full article
Figures

Figure 1

Open AccessArticle
Experimental and Theoretical Investigation of Lowering the Band Gaps of Phononic Crystal Beams through Fluid-Solid Coupling
Crystals 2017, 7(12), 366; doi:10.3390/cryst7120366 -
Abstract
We experimentally and theoretically investigate the band-gap and transmission properties of phononic crystal (PC) beams immersed in water. Spectral element method (SEM) is developed for theoretical analysis in which the hydrodynamic loading is taken into consideration. Influence of the hydrodynamic loading on band-gap
[...] Read more.
We experimentally and theoretically investigate the band-gap and transmission properties of phononic crystal (PC) beams immersed in water. Spectral element method (SEM) is developed for theoretical analysis in which the hydrodynamic loading is taken into consideration. Influence of the hydrodynamic loading on band-gap and transmission properties of the PC beams are studied. To directly detect the displacement transmission of a fully or partially submerged PC beam, a fiber Bragg grating (FBG) displacement sensing system is set up. Agreement between the experimental results and theoretical/numerical calculations also indicates the excellent dynamic sensing performance of the FBG sensing system in the research of the fluid-structure interaction (FSI) problem. Obvious lowering of the band gaps due to fluid-solid coupling is clearly demonstrated. The results in this work might be useful in research such as active tuning of the band gap and transmission properties of the PCs through fluid-solid coupling. Full article
Figures

Figure 1

Open AccessArticle
The Influence of Liquid on the Outcome of Halogen-Bonded Metal–Organic Materials Synthesis by Liquid Assisted Grinding
Crystals 2017, 7(12), 363; doi:10.3390/cryst7120363 -
Abstract
In this work, we describe novel multi-component halogen bonded solids of Co(ii) complexes and 1,4-diiodotetrafluorobenzene, 14tfib. We present the important influence of liquid on the outcome of liquid assisted grinding of dichlorobis(1,10-phenantroline)cobalt(ii), CoCl2(phen)2
[...] Read more.
In this work, we describe novel multi-component halogen bonded solids of Co(ii) complexes and 1,4-diiodotetrafluorobenzene, 14tfib. We present the important influence of liquid on the outcome of liquid assisted grinding of dichlorobis(1,10-phenantroline)cobalt(ii), CoCl2(phen)2 and 14tfib. Grinding of solid reactants with a small amount of water gives the cocrystal product [CoCl2(phen)2](14tfib) (1) while grinding with a small amount of methanol gives an ionic structure, the four-component solid [CoCl(MeOH)(phen)2]Cl(14tfib)(MeOH) (2). Both solid products were also obtained by crystallization from the solution. Single crystal X-ray diffraction reveals that the dominant supramolecular interaction in 1 is the I···Cl halogen bond between 14tfib and CoCl2(phen)2 building blocks. On the other hand, the dominant supramolecular interactions in 2 are I···Cl charge-assisted halogen bonds between the halogen bond donor and the chloride anion as well as hydrogen bonds between the chloride anion and OH groups of coordinated and solvated methanol molecules. Full article
Figures

Open AccessArticle
Reversible Single-Crystal-to-Single-Crystal Structural Transformation in a Mixed-Ligand 2D Layered Metal-Organic Framework: Structural Characterization and Sorption Study
Crystals 2017, 7(12), 364; doi:10.3390/cryst7120364 -
Abstract
A 3D supramolecular network, [Cd(bipy)(C4O4)(H2O)2]·3H2O (1) (bipy = 4,4′-bipyridine and C4O42− = dianion of H2C4O4), constructed by mixed-ligand two-dimensional (2D) metal-organic
[...] Read more.
A 3D supramolecular network, [Cd(bipy)(C4O4)(H2O)2]·3H2O (1) (bipy = 4,4′-bipyridine and C4O42− = dianion of H2C4O4), constructed by mixed-ligand two-dimensional (2D) metal-organic frameworks (MOFs) has been reported and structurally determined by the single-crystal X-ray diffraction method and characterized by other physicochemical methods. In 1, the C4O42− and bipy both act as bridging ligands connecting the Cd(II) ions to form a 2D layered MOF, which are then extended to a 3D supramolecular network via the mutually parallel and interpenetrating arrangements among the 2D-layered MOFs. Compound 1 shows a two-step dehydration process with weight losses of 11.0% and 7.3%, corresponding to the weight-loss of three guest and two coordinated water molecules, respectively, and exhibits an interesting reversible single-crystal-to-single-crystal (SCSC) structural transformation upon de-hydration and re-hydration for guest water molecules. The SCSC structural transformation have been demonstrated and monitored by single-crystal and X-ray powder diffraction, and thermogravimetic analysis studies. Full article
Figures

Figure 1

Open AccessArticle
Growth of Calcite in Confinement
Crystals 2017, 7(12), 361; doi:10.3390/cryst7120361 -
Abstract
Slow growth of calcite in confinement is abundant in Nature and man-made materials. There is ample evidence that such confined growth may create forces that fracture solids. The thermodynamic limits are well known, but since confined crystal growth is transport limited and difficult
[...] Read more.
Slow growth of calcite in confinement is abundant in Nature and man-made materials. There is ample evidence that such confined growth may create forces that fracture solids. The thermodynamic limits are well known, but since confined crystal growth is transport limited and difficult to control in experiments, we have almost no information on the mechanisms or limits of these processes. We present a novel approach to the in situ study of confined crystal growth using microfluidics for accurate control of the saturation state of the fluid and interferometric measurement of the topography of the growing confined crystal surface. We observe and quantify diffusion-limited confined growth rims and explain them with a mass balance model. We have quantified and modeled crystals “floating” on a fluid film of 25–50 nm in thickness due to the disjoining pressure. We find that there are two end-member nanoconfined growth behaviors: (1) smooth and (2) rough intermittent growth, the latter being faster than the former. The intermittent growth rims have regions of load- bearing contacts that move around the rim causing the crystal to “wobble” its way upwards. We present strong evidence that the transition from smooth to rough is a generic confinement-induced instability not limited to calcite. Full article
Figures

Figure 1

Open AccessArticle
Study of Anisotropic Plastic Behavior in High Pressure Torsion of Aluminum Single Crystal by Crystal Plasticity Finite Element Method
Crystals 2017, 7(12), 362; doi:10.3390/cryst7120362 -
Abstract
In this study, a crystal plasticity finite element method (CPFEM) model has been developed to investigate the anisotropic plastic behavior of (001) aluminum single crystal during high-pressure torsion (HPT). The distributions of equivalent plastic strain and Mises stress recorded on the sample surface
[...] Read more.
In this study, a crystal plasticity finite element method (CPFEM) model has been developed to investigate the anisotropic plastic behavior of (001) aluminum single crystal during high-pressure torsion (HPT). The distributions of equivalent plastic strain and Mises stress recorded on the sample surface are presented. The directional variations of plastic strain and Mises stress with the development of four-fold symmetry pattern are observed along the sample circumference. The crystallographic orientation evolution along the tangential direction is studied, and the corresponding lattice rotation and slip trace are predicted, respectively. The plastic anisotropy mechanism is discussed in detail based on the theory of crystal plasticity. The simulation results reveal that the differences in slip systems activation (dominant slip and multiple slips) are responsible for the anisotropic plastic deformation in HPT. Full article
Figures

Figure 1

Open AccessArticle
Remote Access Revolution: Chemical Crystallographers Enter a New Era at Diamond Light Source Beamline I19
Crystals 2017, 7(12), 360; doi:10.3390/cryst7120360 -
Abstract
Since the inception of the use of synchrotron radiation in the structural characterisation of crystalline materials by single-crystal diffraction in the late 20th century, the field has undergone an explosion of technological developments. These cover all aspects of the experiments performed, from the
[...] Read more.
Since the inception of the use of synchrotron radiation in the structural characterisation of crystalline materials by single-crystal diffraction in the late 20th century, the field has undergone an explosion of technological developments. These cover all aspects of the experiments performed, from the construction of the storage rings and insertion devices, to the end user functionalities in the experimental hutches. Developments in automation have most frequently been driven by the macromolecular crystallography community. The drive towards greater access to ever-brighter X-ray sources has benefited the entire field. Herein, we detail the revolution that is now occurring within the chemical crystallography community, utilising many of the tools developed by their more biologically oriented colleagues, along with specialised functionalities that are tailored to the small-molecule world. We discuss the benefits of utilising the advanced features of Diamond Light Source beamline I19 in the newly developed remote access mode and the step-change in productivity that can be established as a result. Full article
Figures

Figure 1

Open AccessArticle
Structurally Complex Frank–Kasper Phases and Quasicrystal Approximants: Electronic Origin of Stability
Crystals 2017, 7(12), 359; doi:10.3390/cryst7120359 -
Abstract
Metal crystals with tetrahedral packing are known as Frank–Kasper phases, with large unit cells with the number of atoms numbering from hundreds to thousands. The main factors of the formation and stability of these phases are the atomic size ratio and the number
[...] Read more.
Metal crystals with tetrahedral packing are known as Frank–Kasper phases, with large unit cells with the number of atoms numbering from hundreds to thousands. The main factors of the formation and stability of these phases are the atomic size ratio and the number of valence electrons per atom. The significance of the electronic energy contribution is analyzed within the Fermi sphere–Brillouin zone interaction model for several typical examples: Cu4Cd3, Mg2Al3 with over a thousand atoms per cell, and for icosahedral quasicrystal approximants with 146–168 atoms per cell. Our analysis shows that to minimize the crystal energy, it is important that the Fermi sphere (FS) is in contact with the Brillouin zones that are related to the strong diffraction peaks: the zones either inscribe the FS or are circumscribed by the FS creating contact at edges or vertices. Full article
Figures

Figure 1

Open AccessArticle
A Different View of Solvent Effects in Crystallization
Crystals 2017, 7(12), 357; doi:10.3390/cryst7120357 -
Abstract
Solvents are widely used in crystallization, but their effects on the shape development of crystals are under debate. Here, we report a view on how solvents play their role by considering the viscosity of solvents. We synthesize silver particles in a mixture of
[...] Read more.
Solvents are widely used in crystallization, but their effects on the shape development of crystals are under debate. Here, we report a view on how solvents play their role by considering the viscosity of solvents. We synthesize silver particles in a mixture of alcohol and water. The viscosity of the solvent is changed by varying the volume ratio of alcohol in water. With the variation of viscosity, diverse morphologies of silver particles are synthesized. Small cubic crystals are formed at low viscosity, while hierarchical flower-like particles are formed at high viscosity. Two alcohols are employed, namely ethanol and propanol. No matter which alcohol is employed, the results are similar. Due to the limitation of mass transfer at high viscosity, the particles synthesized in such solvent are smaller and stabilized by the solvent. When the solution containing these particles are dropped onto metal substrates, these tiny particles firstly aggregate, which is followed by classic crystallization, forming flower-like hierarchical structures. These findings show the importance of the viscosity of solvents in shaping particles, which is underestimated previously. Full article
Figures

Open AccessArticle
Persistence of Smectic-A Oily Streaks into the Nematic Phase by UV Irradiation of Reactive Mesogens
Crystals 2017, 7(12), 358; doi:10.3390/cryst7120358 -
Abstract
Thin smectic liquid crystal films with competing boundary conditions (planar and homeotropic at opposing surfaces) form well-known striated structures known as “oily streaks”, which are a series of hemicylindrical caps that run perpendicular to the easy axis of the planar substrate. The streaks
[...] Read more.
Thin smectic liquid crystal films with competing boundary conditions (planar and homeotropic at opposing surfaces) form well-known striated structures known as “oily streaks”, which are a series of hemicylindrical caps that run perpendicular to the easy axis of the planar substrate. The streaks vanish on heating into the nematic phase, where the film becomes uniform and exhibits hybrid alignment. On adding sufficient reactive mesogen and polymerizing, the oily streak texture is maintained on heating through the entire nematic phase until reaching the bulk isotropic phase, above which the texture vanishes. Depending on the liquid crystal thickness, the oily streak structure may be retrieved after cooling, which demonstrates the strong impact of the polymer backbone on the liquid crystal texture. Polarizing optical, atomic force, and scanning electron microscopy data are presented. Full article
Figures

Figure 1

Open AccessArticle
Structural Characterization of Perpendicularly Aligned Submicrometer-Thick Synthetic Glycolipid Polycrystalline Films Using Conventional X-ray Diffraction
Crystals 2017, 7(12), 356; doi:10.3390/cryst7120356 -
Abstract
The structural analysis of the synthetic glycolipid crystalline phase has been performed during the past few decades; however, it has not been sufficiently understood in terms of both static and dynamic aspects. We have recently shown that grazing incidence X-ray diffraction (GIXD) affords
[...] Read more.
The structural analysis of the synthetic glycolipid crystalline phase has been performed during the past few decades; however, it has not been sufficiently understood in terms of both static and dynamic aspects. We have recently shown that grazing incidence X-ray diffraction (GIXD) affords better information than conventional powder X-ray diffraction (PXRD) for the crystal structure analysis of octyl β-d-galactoside (MOβGal) using sub-micrometer-thick crystalline films and a two-dimensional detector, together with a synchrotron radiation source. However, access to this technique is not universal because of the limited machine time at the required synchrotron radiation sources. Herein, we employed XRD analysis on MOβGal hemihydrate crystalline films using commercial X-ray sources instead of synchrotron radiation sources to extend the availability of the methodology. We investigated some technical aspects of the methodology, such as incident angle and radiation time, using MOβGal polycrystalline films with different thicknesses in order to obtain sufficient reciprocal data for identifying the lattice constants with conventional X-ray sources. Complementary uses of GIXD with a two-dimensional detector, with much higher incident angles than the total reflection angle using a NANO-Viewer system and out-of-plane and in-plane measurements using SmartLab, enabled us to determine the complete lattice parameters for the MOβGal hemihydrate crystalline film. Full article
Figures

Figure 1

Open AccessArticle
Crystallization of Calcium Carbonate in Alginate and Xanthan Hydrogels
Crystals 2017, 7(12), 355; doi:10.3390/cryst7120355 -
Abstract
Calcium carbonate polymorphs were crystallized in alginate and xanthan hydrogels in which a degree of entanglement was altered by the polysaccharide concentration. Both hydrogels contain functional groups (COOH and OH) attached at diverse proportions on saccharide units. In all systems, the precipitation process
[...] Read more.
Calcium carbonate polymorphs were crystallized in alginate and xanthan hydrogels in which a degree of entanglement was altered by the polysaccharide concentration. Both hydrogels contain functional groups (COOH and OH) attached at diverse proportions on saccharide units. In all systems, the precipitation process was initiated simultaneously with gelation, by the fast mixing of the calcium and carbonate solutions, which contain the polysaccharide molecules at respective concentrations. The initial supersaturation was adjusted to be relatively high in order to ensure the conditions suitable for nucleation of all CaCO3 polymorphs and amorphous phase(s). In the model systems (no polysaccharide), a mixture of calcite, vaterite and amorphous calcium carbonate initially precipitated, but after short time only calcite remained. In the presence of xanthan hydrogels, precipitation of either, calcite single crystals, porous polyhedral aggregates, or calcite/vaterite mixtures were observed after five days of ageing, because of different degrees of gel entanglement. At the highest xanthan concentrations applied, the vaterite content was significantly higher. In the alginate hydrogels, calcite microcrystalline aggregates, rosette-like and/or stuck-like monocrystals and vaterite/calcite mixtures precipitated as well. Time resolved crystallization experiments performed in alginate hydrogels indicated the initial formation of a mixture of calcite, vaterite and amorphous calcium carbonate, which transformed to calcite after 24 h of ageing. Full article
Figures

Figure 1

Open AccessArticle
Synthesis, Crystal Structure and Luminescent Properties of 2D Zinc Coordination Polymers Based on Bis(1,2,4-triazol-1-yl)methane and 1,3-Bis(1,2,4-triazol-1-yl)propane
Crystals 2017, 7(12), 354; doi:10.3390/cryst7120354 -
Abstract
Two new two-dimensional zinc(II) coordination polymers containing 2,5-thiophenedicarboxylate and bitopic ligands bis(1,2,4-triazol-1-yl)methane (btrm) or 1,3-bis(1,2,4-triazol-1-yl)propane (btrp) were synthesized. Synthesized compounds were characterized by IR spectroscopy, elemental analysis, powder X-ray diffraction, and thermal analysis. Crystal structures of coordination polymers were determined and their structural
[...] Read more.
Two new two-dimensional zinc(II) coordination polymers containing 2,5-thiophenedicarboxylate and bitopic ligands bis(1,2,4-triazol-1-yl)methane (btrm) or 1,3-bis(1,2,4-triazol-1-yl)propane (btrp) were synthesized. Synthesized compounds were characterized by IR spectroscopy, elemental analysis, powder X-ray diffraction, and thermal analysis. Crystal structures of coordination polymers were determined and their structural peculiarities are discussed. The differences in structural features, thermal behavior, and luminescent properties are discussed. Full article
Figures

Open AccessArticle
Freeform Phononic Waveguides
Crystals 2017, 7(12), 353; doi:10.3390/cryst7120353 -
Abstract
We employ a recently introduced class of artificial structurally-disordered phononic structures that exhibit large and robust elastic frequency band gaps for efficient phonon guiding. Phononic crystals are periodic structures that prohibit the propagation of elastic waves through destructive interference and exhibit large band
[...] Read more.
We employ a recently introduced class of artificial structurally-disordered phononic structures that exhibit large and robust elastic frequency band gaps for efficient phonon guiding. Phononic crystals are periodic structures that prohibit the propagation of elastic waves through destructive interference and exhibit large band gaps and ballistic propagation of elastic waves in the permitted frequency ranges. In contrast, random-structured materials do not exhibit band gaps and favour localization or diffusive propagation. Here, we use structures with correlated disorder constructed from the so-called stealthy hyperuniform disordered point patterns, which can smoothly vary from completely random to periodic (full order) by adjusting a single parameter. Such amorphous-like structures exhibit large band gaps (comparable to the periodic ones), both ballistic-like and diffusive propagation of elastic waves, and a large number of localized modes near the band edges. The presence of large elastic band gaps allows the creation of waveguides in hyperuniform materials, and we analyse various waveguide architectures displaying nearly 100% transmission in the GHz regime. Such phononic-circuit architectures are expected to have a direct impact on integrated micro-electro-mechanical filters and modulators for wireless communications and acousto-optical sensing applications. Full article
Figures

Figure 1