Crystals

2870 KiB

Open AccessArticle

The Influence of Epitaxial Crystallization on the Mechanical Properties of Polyamide 66/Reduced Graphene Oxide Nanocomposite Injection Bar

by Enyi Chi, Minfang An, Guibin Yao, Feng Tian and Zongbao Wang

Crystals 2017, 7(12), 384; https://doi.org/10.3390/cryst7120384 - 20 Dec 2017

Cited by 14 | Viewed by 4066

Abstract

Polyamide 66 (PA66) was chosen as the representative of hydrophilic polymers, to investigate the influence of epitaxial crystals in semi-crystalline polymers/reduced graphene oxide nanocomposite injection-molding bars. A differential scanning calorimeter was used, and the two-dimensional wide-angle X-ray diffraction technique, as well as the [...] Read more.

Polyamide 66 (PA66) was chosen as the representative of hydrophilic polymers, to investigate the influence of epitaxial crystals in semi-crystalline polymers/reduced graphene oxide nanocomposite injection-molding bars. A differential scanning calorimeter was used, and the two-dimensional wide-angle X-ray diffraction technique, as well as the two-dimensional small angle X-ray scattering technique, were used to research the crystallization behavior in PA66/RGO nanocomposites. The results indicated that RGO was an effective nucleation agent for PA66. The presence of RGO could enhance the orientation degree of the PA66 crystals and did not influence the crystal structure of the PA66. The non-epitaxial crystals and the epitaxial crystals existed in PA66/RGO nanocomposites. The size of epitaxial crystals was much greater than that of the non-epitaxial crystals. Tensile test results showed that the presence of fewer epitaxial crystals can improve the mechanical properties of a polymer. Full article

(This article belongs to the Special Issue Graphene Mechanics)

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17993 KiB

Open AccessArticle

Far-field and Fresnel Liquid Crystal Geometric Phase Holograms via Direct-Write Photo-Alignment

by Xiao Xiang, Jihwan Kim and Michael J. Escuti

Crystals 2017, 7(12), 383; https://doi.org/10.3390/cryst7120383 - 20 Dec 2017

Cited by 17 | Viewed by 5928

Abstract

We study computer-generated geometric-phase holograms (GPHs) realized by photo-aligned liquid crystals, in both simulation and experiment. We demonstrate both far-field and Fresnel holograms capable of producing far-field and near-field images with preserved fidelity for all wavelengths. The GPHs are fabricated by patterning a [...] Read more.

We study computer-generated geometric-phase holograms (GPHs) realized by photo-aligned liquid crystals, in both simulation and experiment. We demonstrate both far-field and Fresnel holograms capable of producing far-field and near-field images with preserved fidelity for all wavelengths. The GPHs are fabricated by patterning a photo-alignment layer (PAL) using a direct-write laser scanner and coating the surface with a polymerizable liquid crystal (i.e., a reactive mesogen). We study various recording pixel sizes, down to 3 μm, that are easily recorded in the PAL. We characterize the fabricated elements and find good agreement with theory and numerical simulation. Because of the wavelength independent geometric phase, the (phase) fidelity of the replay images is preserved for all wavelengths, unlike conventional dynamic phase holograms. However, governed by the diffraction equation, the size and location of a reconstructed image depends on the replay wavelength for far-field and near-field GPHs, respectively. These offer interesting opportunities for white-light holography. Full article

(This article belongs to the Section Liquid Crystals)

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18898 KiB

Open AccessReview

Chemical Crystallography at the Advanced Light Source

by Laura J. McCormick, Nico Giordano, Simon J. Teat and Christine M. Beavers

Crystals 2017, 7(12), 382; https://doi.org/10.3390/cryst7120382 - 18 Dec 2017

Cited by 6 | Viewed by 6219

Abstract

Chemical crystallography at synchrotrons was pioneered at the Daresbury SRS station 9.8. The chemical crystallography beamlines at the Advanced Light Source seek to follow that example, with orders of magnitude more flux than a lab source, and various in situ experiments. This article [...] Read more.

Chemical crystallography at synchrotrons was pioneered at the Daresbury SRS station 9.8. The chemical crystallography beamlines at the Advanced Light Source seek to follow that example, with orders of magnitude more flux than a lab source, and various in situ experiments. This article attempts to answer why a chemist would require synchrotron X-rays, to describe the techniques available at the ALS chemical crystallography beamlines, and place the current facilities in a historical context. Full article

(This article belongs to the Special Issue Advances in Synchrotron Radiation Applications for Crystal Structure Studies)

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7396 KiB

Open AccessArticle

High-Pressure Synthesis, Structure, and Magnetic Properties of Ge-Substituted Filled Skutterudite Compounds; Ln_xCo₄Sb_12−yGe_y, Ln = La, Ce, Pr, and Nd

by Hiroshi Fukuoka

Crystals 2017, 7(12), 381; https://doi.org/10.3390/cryst7120381 - 15 Dec 2017

Cited by 2 | Viewed by 3005

Abstract

A series of new Ge-substituted skutterudite compounds with the general composition of Ln_xCo₄Sb_12−yGe_y, where Ln = La, Ce, Pr, and Nd, is prepared by high-pressure and high-temperature reactions at 7 GPa and 800 °C. [...] Read more.

A series of new Ge-substituted skutterudite compounds with the general composition of Ln_xCo₄Sb_12−yGe_y, where Ln = La, Ce, Pr, and Nd, is prepared by high-pressure and high-temperature reactions at 7 GPa and 800 °C. They have a cubic unit cell and the lattice constant for each compound is 8.9504 (3), 8.94481 (6), 8.9458 (3), and 8.9509 (4) Å for the La, Ce, Pr, and Nd derivatives, respectively. Their chemical compositions, determined by electron prove microanalysis, are La_0.57Co₄Sb_10.1Ge_2.38, Ce_0.99Co₄Sb_9.65Ge_2.51, Pr_0.97Co₄Sb_9.52Ge_2.61, and Nd_0.87Co₄Sb_9.94Ge_2.28. Their structural parameters are refined by Rietveld analysis. The guest atom size does not affect the unit cell volume. The Co–Sb/Ge distance mainly determines the unit cell size as well as the size of guest atom site. The valence state of lanthanide ions is 3+. Full article

(This article belongs to the Special Issue High-Pressure Studies of Crystalline Materials)

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18733 KiB

Open AccessArticle

The Effect of the Vertex Angles of Wedged Indenters on Deformation during Nanoindentation

by Xiaowen Hu and Yushan Ni

Crystals 2017, 7(12), 380; https://doi.org/10.3390/cryst7120380 - 14 Dec 2017

Cited by 2 | Viewed by 3576

Abstract

In order to study the effect of the angle of wedged indenters during nanoindentation, indenters with half vertex angles of 60°, 70° and 80° are used for the simulations of nanoindentation on FCC aluminum (Al) bulk material by the multiscale quasicontinuum method (QC). [...] Read more.

In order to study the effect of the angle of wedged indenters during nanoindentation, indenters with half vertex angles of 60°, 70° and 80° are used for the simulations of nanoindentation on FCC aluminum (Al) bulk material by the multiscale quasicontinuum method (QC). The load-displacement responses, the strain energy-displacement responses, and hardness of Al bulk material are obtained. Besides, atomic configurations for each loading situation are presented. We analyze the drop points in the load-displacement responses, which correspond to the changes of microstructure in the bulk material. From the atom images, the generation of partial dislocations as well as the nucleation and the emission of perfect dislocations have been observed with wedged indenters of half vertex angles of 60° and 70°, but not 80°. The stacking faults move beneath the indenter along the direction

[1 \bar{1} 0]

. The microstructures of residual displacements are also discussed. In addition, hardness of the Al bulk material is different in simulations with wedged indenters of half vertex angles of 60° and 70°, and critical hardness in the simulation with the 70° indenter is bigger than that with the 60° indenter. The size effect of hardness in plastic wedged nanoindentation is observed. There are fewer abrupt drops in the strain energy-displacement response than in the load-displacement response, and the abrupt drops in strain energy-displacement response reflect the nucleation of perfect dislocations or extended dislocations rather than partial dislocations. The wedged indenter with half vertex angle of 70° is recommended for investigating dislocations during nanoindentation. Full article

(This article belongs to the Special Issue Crystal Indentation Hardness)

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5859 KiB

Open AccessArticle

Influence of Alkali Metal Substitution on the Phase Transition Behavior of CsGaQ₂ (Q = S, Se)

by Daniel Friedrich, Marc Schlosser, Martin Etter and Arno Pfitzner

Crystals 2017, 7(12), 379; https://doi.org/10.3390/cryst7120379 - 14 Dec 2017

Cited by 9 | Viewed by 4462

Abstract

The formation of solid solution series Cs_1−xM_xGaQ₂-mC64 (M = K, Rb; Q = S, Se; x = 0–1) was studied by X-ray diffraction and spectroscopic methods, revealing a complete miscibility of CsGa [...] Read more.

The formation of solid solution series Cs_1−xM_xGaQ₂-mC64 (M = K, Rb; Q = S, Se; x = 0–1) was studied by X-ray diffraction and spectroscopic methods, revealing a complete miscibility of CsGaQ₂-mC64 with RbGaQ₂ and KGaSe₂, and a large miscibility gap with KGaS₂. All solid solution members exhibit similar Raman spectra, indicating the covalent Ga-Q bonding character. The similar optical band gaps likewise further contribute to this conclusion. Up to a certain degree of substitution, these solid solutions undergo a phase transition similar to CsGaQ₂-mC64. The influence of the substitution parameter x on phase transition process was investigated in situ using high-temperature X-ray powder diffraction experiments. Phase-pure solid solutions of the high-temperature polymorphs Cs_1−xM_xGaQ₂-mC16 were obtained up to x_max(K) = 0.1 and x_max(Rb) = 0.3. The crystal structures of these new CsGaQ₂-mC16 analogous high-temperature phases were refined from synchrotron diffraction data by Rietveld-refinement. Full article

(This article belongs to the Special Issue Synthesis and Structural Investigations of Polymorphic Compounds)

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2515 KiB

Open AccessArticle

Thermal Stability of Epitaxial Graphene Electrodes for Conductive Polymer Nanofiber Devices

by Kyung Ho Kim, Samuel Lara-Avila, Hans He, Hojin Kang, Yung Woo Park, Rositsa Yakimova and Sergey Kubatkin

Crystals 2017, 7(12), 378; https://doi.org/10.3390/cryst7120378 - 14 Dec 2017

Cited by 3 | Viewed by 3793

Abstract

We used large area, monolayer graphene epitaxially grown on SiC (0001) as contact electrodes for polymer nanofiber devices. Our fabrication process, which avoids polymer resist residues on the graphene surface, results in graphene-polyaniline nanofiber devices with Ohmic contacts and electrical conductivity comparable to [...] Read more.

We used large area, monolayer graphene epitaxially grown on SiC (0001) as contact electrodes for polymer nanofiber devices. Our fabrication process, which avoids polymer resist residues on the graphene surface, results in graphene-polyaniline nanofiber devices with Ohmic contacts and electrical conductivity comparable to that of Au-nanofiber devices. We further checked the thermal stability of the graphene contacts to polyaniline devices by annealing up to T = 800 °C, the temperature at which polyaniline nanofibers are carbonized but the graphene electrode remains intact. The thermal stability and Ohmic contact of polymer nanofibers are demonstrated here, which together with the chemical stability and atomic flatness of graphene, make epitaxial graphene on SiC an attractive contact material for future all-carbon electronic devices. Full article

(This article belongs to the Special Issue Integration of 2D Materials for Electronics Applications)

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1665 KiB

Open AccessArticle

Crystallization, Structure Determination and Reticular Twinning in Iron(III) Salicylate: Fe[(HSal)(Sal)(H₂O)₂]

by Jitschaq Anne Van der Horn, Bernd Souvignier and Martin Lutz

Crystals 2017, 7(12), 377; https://doi.org/10.3390/cryst7120377 - 14 Dec 2017

Cited by 6 | Viewed by 9057

Abstract

In this contribution, we present the first crystal structure of iron(III) salicylate without additional counterions. The octahedral complex contains two salicylate and two water molecules as ligands. One salicylate is mono-anionic while the other is di-anionic. Because of the centrosymmetry of the complex, [...] Read more.

In this contribution, we present the first crystal structure of iron(III) salicylate without additional counterions. The octahedral complex contains two salicylate and two water molecules as ligands. One salicylate is mono-anionic while the other is di-anionic. Because of the centrosymmetry of the complex, the acidic hydrogen atom is disordered on the midpoint between two salicylate oxygens. The structure determination of the tiny crystal indicates the presence of reticular twinning. The structure solution of the twin is shown and an explanation based on the crystal packing is provided. Full article

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4328 KiB

Open AccessReview

Aromatic C-Nitroso Compounds and Their Dimers: A Model for Probing the Reaction Mechanisms in Crystalline Molecular Solids

by Ivana Biljan and Hrvoj Vančik

Crystals 2017, 7(12), 376; https://doi.org/10.3390/cryst7120376 - 14 Dec 2017

Cited by 12 | Viewed by 6454

Abstract

This review is focused on the dimerization and dissociation of aromatic C-nitroso compounds and their dimers, the reactions that could be used as a convenient model for studying the thermal organic solid-state reaction mechanisms. This molecular model is simple because it includes formation [...] Read more.

This review is focused on the dimerization and dissociation of aromatic C-nitroso compounds and their dimers, the reactions that could be used as a convenient model for studying the thermal organic solid-state reaction mechanisms. This molecular model is simple because it includes formation or breaking of only one covalent bond between two nitrogen atoms. The crystalline molecular solids of nitroso dimers (azodioxides) dissociate by photolysis under the cryogenic conditions, and re-dimerize by slow warming. The thermal re-dimerization reaction is examined under the different topotactic conditions in crystals: disordering, surface defects, and phase transformations. Depending on the conditions, and on the molecular structure, aromatic C-nitroso compounds can associate to form one-dimensional polymeric structures and are able to self-assemble on gold surfaces. Full article

(This article belongs to the Special Issue Photocrystallography and Solid-State Structural Dynamics)

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1019 KiB

Open AccessReview

Defects in Static Elasticity of Quasicrystals

by Qin Xu, Jing Lu and Wu Li

Crystals 2017, 7(12), 373; https://doi.org/10.3390/cryst7120373 - 14 Dec 2017

Viewed by 3244

Abstract

A review on mathematical elasticity of quasicrystals is given. In this review, the focus is on various defects of quasicrystals. Dislocation and crack are two classes of typical topological defects, while their existence has great influence on the mechanical behavior of quasicrystals. The [...] Read more.

A review on mathematical elasticity of quasicrystals is given. In this review, the focus is on various defects of quasicrystals. Dislocation and crack are two classes of typical topological defects, while their existence has great influence on the mechanical behavior of quasicrystals. The analytic and numerical solutions of dislocations and crack in quasicrystals are the core of the static and dynamic elasticity theory, and this paper gives a comprehensive review on the solutions for dislocations and crack with different configurations in different various important quasicrystalline systems. We review some results in linear elasticity of quasicrystals, referring to different boundary value problems. We also add some new achievements. Full article

(This article belongs to the Special Issue Structure and Properties of Quasicrystalline Materials)

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5391 KiB

Open AccessArticle

Stable Stacking Faults Bounded by Frank Partial Dislocations in Al7075 Formed through Precipitate and Dislocation Interactions

by Sijie Li, Hongyun Luo, Hui Wang, Pingwei Xu, Jun Luo, Chu Liu and Tao Zhang

Crystals 2017, 7(12), 375; https://doi.org/10.3390/cryst7120375 - 13 Dec 2017

Cited by 6 | Viewed by 8966

Abstract

Through high-resolution electron microscopy, stacking faults (SFs) due to Frank partial dislocations were found in an aluminum alloy following deformation with low strain and strain rate, while also remaining stable during artificial aging. Extrinsic stacking faults were found surrounded by dislocation areas and [...] Read more.

Through high-resolution electron microscopy, stacking faults (SFs) due to Frank partial dislocations were found in an aluminum alloy following deformation with low strain and strain rate, while also remaining stable during artificial aging. Extrinsic stacking faults were found surrounded by dislocation areas and precipitates. An intrinsic stacking fault was found between two Guinier-Preston II (GP II) zones when the distance of the two GP II zones was 2 nm. Defects (precipitates and dislocations) are considered to have an influence on the formation of the SFs, as their appearance may cause local strain and promote the gathering of vacancies to lower the energy. Full article

(This article belongs to the Special Issue Crystal Dislocations: Their Impact on Physical Properties of Crystals)

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1771 KiB

Open AccessArticle

Influence of External Static Magnetic Fields on Properties of Metallic Functional Materials

by Xiaowei Zuo, Lin Zhang and Engang Wang

Crystals 2017, 7(12), 374; https://doi.org/10.3390/cryst7120374 - 13 Dec 2017

Cited by 9 | Viewed by 3817

Abstract

Influence of external static magnetic fields on solidification, solid phase transformation of metallic materials have been reviewed in terms of Lorentz force, convection, magnetization, orientation, diffusion, and so on. However, the influence of external static magnetic fields on properties of metallic functional materials [...] Read more.

Influence of external static magnetic fields on solidification, solid phase transformation of metallic materials have been reviewed in terms of Lorentz force, convection, magnetization, orientation, diffusion, and so on. However, the influence of external static magnetic fields on properties of metallic functional materials is rarely reviewed. In this paper, the effect of static magnetic fields subjected in solidification and/or annealing on the properties of Fe–Ga magnetostrictive material, high strength high conductivity Cu-based material (Cu–Fe and Cu–Ag alloys), and Fe–Sn magnetic material were summarized. Both the positive and negative impacts from magnetic fields were found. Exploring to maximize the positive influence of magnetic fields is still a very meaningful and scientific issue in future. Full article

(This article belongs to the Special Issue Non-Ambient Crystallography)

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4929 KiB

Open AccessArticle

Phononic Crystal Made of Multilayered Ridges on a Substrate for Rayleigh Waves Manipulation

by Mourad Oudich, Bahram Djafari-Rouhani, Bernard Bonello, Yan Pennec and Frédéric Sarry

Crystals 2017, 7(12), 372; https://doi.org/10.3390/cryst7120372 - 12 Dec 2017

Cited by 21 | Viewed by 5819

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

(This article belongs to the Special Issue Phononics)

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19045 KiB

Open AccessArticle

Vickers Hardness of Diamond and cBN Single Crystals: AFM Approach

by Sergey Dub, Petro Lytvyn, Viktor Strelchuk, Andrii Nikolenko, Yurii Stubrov, Igor Petrusha, Takashi Taniguchi and Sergey Ivakhnenko

Crystals 2017, 7(12), 369; https://doi.org/10.3390/cryst7120369 - 12 Dec 2017

Cited by 40 | Viewed by 15399

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

(This article belongs to the Special Issue Crystal Indentation Hardness)

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4789 KiB

Open AccessArticle

Hydrophobic Calcium Carbonate for Cement Surface

by Shashi B. Atla, Yi-Hsun Huang, James Yang, How-Ji Chen, Yi-Hao Kuo, Chun-Mei Hsu, Wen-Chien Lee, Chien-Cheng Chen, Duen-Wei Hsu and Chien-Yen Chen

Crystals 2017, 7(12), 371; https://doi.org/10.3390/cryst7120371 - 11 Dec 2017

Cited by 19 | Viewed by 7275

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

(This article belongs to the Special Issue Carbonates)

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4349 KiB

Open AccessArticle

Synthesis, Crystal Structure, Gas Absorption, and Separation Properties of a Novel Complex Based on Pr and a Three-Connected Ligand

by Jie Sun, Minghui Zhang, Aiyun Wang and Ziwei Cai

Crystals 2017, 7(12), 370; https://doi.org/10.3390/cryst7120370 - 11 Dec 2017

Cited by 3 | Viewed by 3258

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

(This article belongs to the Special Issue Structural Design and Properties of Coordination Polymers)

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3704 KiB

Open AccessArticle

Improvement in the Photorefractive Response Speed and Mechanism of Pure Congruent Lithium Niobate Crystals by Increasing the Polarization Current

by Tian Tian, Xiaodong Yan, Yongfa Kong, Hongde Liu, Dahuai Zheng, Shiguo Liu, Shaolin Chen, Jingjun Xu and Jiayue Xu

Crystals 2017, 7(12), 368; https://doi.org/10.3390/cryst7120368 - 11 Dec 2017

Cited by 4 | Viewed by 3350

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

(This article belongs to the Special Issue Lithium Niobate: Bulk Crystals, Composites, Thin Films and Nanocrystals)

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2575 KiB

Open AccessArticle

Chalcogenide Quaternary Cu₂FeSnS₄ Nanocrystals for Solar Cells: Explosive Character of Mechanochemical Synthesis and Environmental Challenge

by Peter Baláž, Matej Baláž, María J. Sayagués, Alexander Eliyas, Nina G. Kostova, Mária Kaňuchová, Erika Dutková and Anna Zorkovská

Crystals 2017, 7(12), 367; https://doi.org/10.3390/cryst7120367 - 09 Dec 2017

Cited by 16 | Viewed by 4567

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

(This article belongs to the Special Issue Polymorphism of Mechanochemically Synthesized Cocrystals)

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3096 KiB

Open AccessArticle

Experimental and Theoretical Investigation of Lowering the Band Gaps of Phononic Crystal Beams through Fluid-Solid Coupling

by Xiang Fang, Kuo-Chih Chuang, Zhi-Wen Yuan and Zhi-Long Huang

Crystals 2017, 7(12), 366; https://doi.org/10.3390/cryst7120366 - 08 Dec 2017

Cited by 1 | Viewed by 3607

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

(This article belongs to the Special Issue Phononics)

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1837 KiB

Open AccessArticle

Structural Characterization of Febuxostat/l-Pyroglutamic Acid Cocrystal Using Solid-State ¹³C-NMR and Investigational Study of Its Water Solubility

by Ji-Hun An, Changjin Lim, Hyung Chul Ryu, Jae Sun Kim, Hyuk Min Kim, Alice Nguvoko Kiyonga, Minho Park, Young-Ger Suh, Gyu Hwan Park and Kiwon Jung

Crystals 2017, 7(12), 365; https://doi.org/10.3390/cryst7120365 - 08 Dec 2017

Cited by 15 | Viewed by 7966

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

(This article belongs to the Special Issue Novel Pharmaceutical Cocrystals and Their Applications)

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2266 KiB

Open AccessArticle

Reversible Single-Crystal-to-Single-Crystal Structural Transformation in a Mixed-Ligand 2D Layered Metal-Organic Framework: Structural Characterization and Sorption Study

by Chih-Chieh Wang, Szu-Yu Ke, Kuan-Ting Chen, Yi-Fang Hsieh, Tzu-Heng Wang, Gene-Hsiang Lee and Yu-Chun Chuang

Crystals 2017, 7(12), 364; https://doi.org/10.3390/cryst7120364 - 07 Dec 2017

Cited by 8 | Viewed by 5047

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

(This article belongs to the Special Issue Structural Design and Properties of Coordination Polymers)

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2327 KiB

Open AccessArticle

The Influence of Liquid on the Outcome of Halogen-Bonded Metal–Organic Materials Synthesis by Liquid Assisted Grinding

by Katarina Lisac and Dominik Cinčić

Crystals 2017, 7(12), 363; https://doi.org/10.3390/cryst7120363 - 07 Dec 2017

Cited by 12 | Viewed by 5433

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

(This article belongs to the Special Issue Polymorphism of Mechanochemically Synthesized Cocrystals)

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2227 KiB

Open AccessArticle

Study of Anisotropic Plastic Behavior in High Pressure Torsion of Aluminum Single Crystal by Crystal Plasticity Finite Element Method

by Peitang Wei, Cheng Lu, Huaiju Liu, Lihong Su, Guanyu Deng and Kiet Tieu

Crystals 2017, 7(12), 362; https://doi.org/10.3390/cryst7120362 - 06 Dec 2017

Cited by 7 | Viewed by 4306

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

(This article belongs to the Special Issue Crystal Dislocations: Their Impact on Physical Properties of Crystals)

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2535 KiB

Open AccessArticle

Growth of Calcite in Confinement

by Lei Li, Felix Kohler, Anja Røyne and Dag Kristian Dysthe

Crystals 2017, 7(12), 361; https://doi.org/10.3390/cryst7120361 - 06 Dec 2017

Cited by 14 | Viewed by 5023

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

(This article belongs to the Special Issue Effects of Confinement and Topography on Crystallization)

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2455 KiB

Open AccessArticle

Remote Access Revolution: Chemical Crystallographers Enter a New Era at Diamond Light Source Beamline I19

by Natalie T. Johnson, Paul G. Waddell, William Clegg and Michael R. Probert

Crystals 2017, 7(12), 360; https://doi.org/10.3390/cryst7120360 - 05 Dec 2017

Cited by 24 | Viewed by 5824

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

(This article belongs to the Special Issue Advances in Synchrotron Radiation Applications for Crystal Structure Studies)

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1896 KiB

Open AccessArticle

Structurally Complex Frank–Kasper Phases and Quasicrystal Approximants: Electronic Origin of Stability

by Valentina F. Degtyareva and Natalia S. Afonikova

Crystals 2017, 7(12), 359; https://doi.org/10.3390/cryst7120359 - 04 Dec 2017

Cited by 2 | Viewed by 3990

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

(This article belongs to the Special Issue Structure and Properties of Quasicrystalline Materials)

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3372 KiB

Open AccessArticle

Persistence of Smectic-A Oily Streaks into the Nematic Phase by UV Irradiation of Reactive Mesogens

by Ines Gharbi, Amine Missaoui, Dominique Demaille, Emmanuelle Lacaze and Charles Rosenblatt

Crystals 2017, 7(12), 358; https://doi.org/10.3390/cryst7120358 - 03 Dec 2017

Cited by 8 | Viewed by 5239

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

(This article belongs to the Section Liquid Crystals)

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6602 KiB

Open AccessArticle

A Different View of Solvent Effects in Crystallization

by Han Wang, Qiang Lin, Xiangyu Dou, Tao Yang and Yongsheng Han

Crystals 2017, 7(12), 357; https://doi.org/10.3390/cryst7120357 - 03 Dec 2017

Cited by 13 | Viewed by 7411

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

(This article belongs to the Section Crystalline Materials)

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23041 KiB

Open AccessArticle

Structural Characterization of Perpendicularly Aligned Submicrometer-Thick Synthetic Glycolipid Polycrystalline Films Using Conventional X-ray Diffraction

by Shigesaburo Ogawa and Isao Takahashi

Crystals 2017, 7(12), 356; https://doi.org/10.3390/cryst7120356 - 01 Dec 2017

Cited by 6 | Viewed by 5214

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

(This article belongs to the Section Crystalline Materials)

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18918 KiB

Open AccessArticle

Crystallization of Calcium Carbonate in Alginate and Xanthan Hydrogels

by Cleo Kosanović, Simona Fermani, Giuseppe Falini and Damir Kralj

Crystals 2017, 7(12), 355; https://doi.org/10.3390/cryst7120355 - 30 Nov 2017

Cited by 23 | Viewed by 10399

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

(This article belongs to the Special Issue Carbonates)

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Crystals, Volume 7, Issue 12 (December 2017) – 33 articles

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