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Crystals, Volume 7, Issue 8 (August 2017)

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Cover Story Graphene, a monoatomic layer of carbon atoms arranged on a honeycomb lattice, exhibits [...] Read more.
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Open AccessArticle Pr9.33(SiO4)6O2 Crystals: Czochralski Growth and Near UV-Visible FR Performance
Crystals 2017, 7(8), 229; doi:10.3390/cryst7080229
Received: 29 June 2017 / Revised: 21 July 2017 / Accepted: 21 July 2017 / Published: 31 July 2017
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Abstract
Pr9.33(SiO4)6O2 crystals have been grown by the Cz-method for the first time for near UV–visible Faraday rotation applications. Rietveld refinement of XRD data demonstrates that the compound crystallizes in the oxyapatite structure with space group P
[...] Read more.
Pr9.33(SiO4)6O2 crystals have been grown by the Cz-method for the first time for near UV–visible Faraday rotation applications. Rietveld refinement of XRD data demonstrates that the compound crystallizes in the oxyapatite structure with space group P63/m, with oxyapatite structure. In contrast to Tb3Ga5O12, Pr9.33(SiO4)6O2 crystal shows a higher transparency in the UV–visible wavelength region, and a shorter cutoff at 270 nm. The Faraday rotation performance and the temperature-dependence of the field-cooled (FC) and zero-field-cooled (ZFC) magnetic susceptibility have been investigated, which indicate that the Pr9.33(SiO4)6O2 crystal exhibits paramagnetic behavior in the experimental temperature range from 2 to 300 K and yields a larger FR angle which rapidly increases towards the cutoff. Pr9.33(SiO4)6O2 crystal is therefore a promising magneto-optical crystal in particular for potential FR applications in the near UV–visible spectral region. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle Lattice Site of Rare-Earth Ions in Stoichiometric Lithium Niobate Probed by OH Vibrational Spectroscopy
Crystals 2017, 7(8), 230; doi:10.3390/cryst7080230
Received: 7 July 2017 / Revised: 20 July 2017 / Accepted: 21 July 2017 / Published: 25 July 2017
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Abstract
Rare-earth (RE = Er3+, Nd3+, or Yb3+) ion-doped stoichiometric LiNbO3 crystals were grown by the Czochralski and the high-temperature top-seeded solution growth methods. For the 0.22–0.87 mol% concentration range of the RE oxides in the melt/solution,
[...] Read more.
Rare-earth (RE = Er3+, Nd3+, or Yb3+) ion-doped stoichiometric LiNbO3 crystals were grown by the Czochralski and the high-temperature top-seeded solution growth methods. For the 0.22–0.87 mol% concentration range of the RE oxides in the melt/solution, in addition to the well-known hydroxyl (OH) vibrational band in undoped stoichiometric LiNbO3, a new infrared absorption band was observed at about 3500 cm−1, similar to the case of the trivalent optical damage resistant (ODR) dopants In3+ and Sc3+. By comparing the frequencies and polarization dependences of the bands to those detected for ODR ion containing crystals, they are attributed to the stretching vibration of OH ions in RE3+Nb-OH complexes. Consequently, above a given concentration threshold, some of the rare-earth ions are assumed to occupy niobium sites in the LiNbO3 lattice. The same model is also suggested for RE-doped congruent LiNbO3 crystals containing over-threshold (>5 mol %) amounts of the Mg-co-dopant. Full article
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Open AccessArticle Non-Destructive In Situ Study of Plastic Deformations in Diamonds: X-ray Diffraction Topography and µFTIR Mapping of Two Super Deep Diamond Crystals from São Luiz (Juina, Brazil)
Crystals 2017, 7(8), 233; doi:10.3390/cryst7080233
Received: 29 June 2017 / Revised: 24 July 2017 / Accepted: 25 July 2017 / Published: 28 July 2017
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Abstract
Diamonds from Juina, Brazil, are well-known examples of superdeep diamond crystals formed under sublithospheric conditions and evidence would indicate their origins lie as deep as the Earth’s mantle transition zone and the Lower Mantle. Detailed characterization of these minerals and of inclusions trapped
[...] Read more.
Diamonds from Juina, Brazil, are well-known examples of superdeep diamond crystals formed under sublithospheric conditions and evidence would indicate their origins lie as deep as the Earth’s mantle transition zone and the Lower Mantle. Detailed characterization of these minerals and of inclusions trapped within them may thus provide precious minero-petrogenetic information on their growth history in these inaccessible environments. With the aim of studying non-destructively the structural defects in the entire crystalline volume, two diamond samples from this locality, labelled JUc4 and BZ270, respectively, were studied in transmission mode by means of X-ray Diffraction Topography (XRDT) and micro Fourier Transform InfraRed Spectroscopy (µFTIR). The combined use of these methods shows a good fit between the mapping of spatial distribution of extended defects observed on the topographic images and the µFTIR maps corresponding to the concentration of N and H point defects. The results obtained show that both samples are affected by plastic deformation. In particular, BZ270 shows a lower content of nitrogen and higher deformation, and actually consists of different, slightly misoriented grains that contain sub-grains with a rounded-elongated shape. These features are commonly associated with deformation processes by solid-state diffusion creep under high pressure and high temperature. Full article
(This article belongs to the Special Issue Diamond Crystals)
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Open AccessArticle On the Derivation of Boundary Conditions for Continuum Dislocation Dynamics
Crystals 2017, 7(8), 235; doi:10.3390/cryst7080235
Received: 10 July 2017 / Revised: 27 July 2017 / Accepted: 28 July 2017 / Published: 30 July 2017
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Abstract
Continuum dislocation dynamics (CDD) is a single crystal strain gradient plasticity theory based exclusively on the evolution of the dislocation state. Recently, we derived a constitutive theory for the average dislocation velocity in CDD in a phase field-type description for an infinite domain.
[...] Read more.
Continuum dislocation dynamics (CDD) is a single crystal strain gradient plasticity theory based exclusively on the evolution of the dislocation state. Recently, we derived a constitutive theory for the average dislocation velocity in CDD in a phase field-type description for an infinite domain. In the current work, so-called rational thermodynamics is employed to obtain thermodynamically consistent boundary conditions for the dislocation density variables of CDD. We find that rational thermodynamics reproduces the bulk constitutive equations as obtained from irreversible thermodynamics. The boundary conditions we find display strong parallels to the microscopic traction conditions derived by Gurtin and Needleman (M.E. Gurtin and A. Needleman, J. Mech. Phys. Solids 53 (2005) 1–31) for strain gradient theories based on the Kröner–Nye tensor. Full article
(This article belongs to the Special Issue Plasticity of Crystals and Interfaces)
Open AccessCommunication Self-Assembled Microwires of Terephthalic Acid and Melamine
Crystals 2017, 7(8), 236; doi:10.3390/cryst7080236
Received: 12 July 2017 / Revised: 26 July 2017 / Accepted: 26 July 2017 / Published: 31 July 2017
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Abstract
Self-assembled microwires of terephthalic acid (TPA) and melamine are prepared through the evaporation of water in a solution mixture of TPA and melamine. The microwires were characterized by using scanning electron microscope (SEM), attenuated total reflection infrared (ATR-IR) spectra, and cross-polarized optical microscopy
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Self-assembled microwires of terephthalic acid (TPA) and melamine are prepared through the evaporation of water in a solution mixture of TPA and melamine. The microwires were characterized by using scanning electron microscope (SEM), attenuated total reflection infrared (ATR-IR) spectra, and cross-polarized optical microscopy (CPOM). The TPA•M microwires showed semi-conductive properties. Full article
(This article belongs to the Special Issue Advance in Crystalline Thin Wires)
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Open AccessArticle The Internal Structure of Yellow Cuboid Diamonds from Alluvial Placers of the Northeastern Siberian Platform
Crystals 2017, 7(8), 238; doi:10.3390/cryst7080238
Received: 30 June 2017 / Revised: 26 July 2017 / Accepted: 28 July 2017 / Published: 31 July 2017
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Abstract
Yellow cuboid diamonds are commonly found in diamondiferous alluvial placers of the Northeastern Siberian platform. The internal structure of these diamonds have been studied by optical microscopy, X-Ray topography (XRT) and electron backscatter diffraction (EBSD) techniques. Most of these crystals have typical resorption
[...] Read more.
Yellow cuboid diamonds are commonly found in diamondiferous alluvial placers of the Northeastern Siberian platform. The internal structure of these diamonds have been studied by optical microscopy, X-Ray topography (XRT) and electron backscatter diffraction (EBSD) techniques. Most of these crystals have typical resorption features and do not preserve primary growth morphology. The resorption leads to an evolution from an originally cubic shape to a rounded tetrahexahedroid. Specific fibrous or columnar internal structure of yellow cuboid diamonds has been revealed. Most of them are strongly deformed. Misorientations of the crystal lattice, found in the samples, may be caused by strains from their fibrous growth or/and post-growth plastic deformation. Full article
(This article belongs to the Special Issue Diamond Crystals)
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Open AccessArticle Effect of Nitrogen Impurities on the Raman Line Width in Diamond, Revisited
Crystals 2017, 7(8), 239; doi:10.3390/cryst7080239
Received: 30 June 2017 / Revised: 25 July 2017 / Accepted: 28 July 2017 / Published: 31 July 2017
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Abstract
The results of a high-resolution Raman scattering study of a diamond crystal with a high content of single substitutional nitrogen impurities (550 ppm) in the temperature range from 50 to 673 K are presented and compared with the data for defect-free diamond. It
[...] Read more.
The results of a high-resolution Raman scattering study of a diamond crystal with a high content of single substitutional nitrogen impurities (550 ppm) in the temperature range from 50 to 673 K are presented and compared with the data for defect-free diamond. It is established that the increase of the nitrogen concentration in diamond leads to the temperature-independent increase of the Raman line width. Analysis of the experimental data allows us to conclude that this broadening should be attributed to the defect-induced shortening of the Raman phonon lifetime. We believe that this mechanism is responsible for the increase of the Raman line width caused by most point-like defects in diamond. No pronounced effects of the nitrogen defects on the Raman line position and phonon anharmonicity are observed. Full article
(This article belongs to the Special Issue Diamond Crystals)
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Open AccessArticle Atomistic Insights into the Effects of Residual Stress during Nanoindentation
Crystals 2017, 7(8), 240; doi:10.3390/cryst7080240
Received: 21 June 2017 / Revised: 26 July 2017 / Accepted: 30 July 2017 / Published: 1 August 2017
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Abstract
The influence of in-plane residual stress on Hertzian nanoindentation for single-crystal copper thin film is investigated using molecular dynamics simulations (MD). It is found that: (i) the yield strength of incipient plasticity increases with compressive residual stress, but decreases with tensile residual stress;
[...] Read more.
The influence of in-plane residual stress on Hertzian nanoindentation for single-crystal copper thin film is investigated using molecular dynamics simulations (MD). It is found that: (i) the yield strength of incipient plasticity increases with compressive residual stress, but decreases with tensile residual stress; (ii) the hardness decreases with tensile residual stress, and increases with compressive residual stress, but abruptly drops down at a higher compressive residual stress level, because of the deterioration of the surface; (iii) the indentation modulus reduces linearly with decreasing compressive residual stress (and with increasing tensile residual stress). It can be concluded from the MD simulations that the residual stress not only strongly influences the dislocation evolution of the plastic deformation process, but also significantly affects the size of the plastic zone. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessArticle A Novel Approach to Data Collection for Difficult Structures: Data Management for Large Numbers of Crystals with the BLEND Software
Crystals 2017, 7(8), 242; doi:10.3390/cryst7080242
Received: 11 July 2017 / Revised: 26 July 2017 / Accepted: 31 July 2017 / Published: 4 August 2017
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Abstract
The present article describes how to use the computer program BLEND to help assemble complete datasets for the solution of macromolecular structures, starting from partial or complete datasets, derived from data collection from multiple crystals. The program is demonstrated on more than two
[...] Read more.
The present article describes how to use the computer program BLEND to help assemble complete datasets for the solution of macromolecular structures, starting from partial or complete datasets, derived from data collection from multiple crystals. The program is demonstrated on more than two hundred X-ray diffraction datasets obtained from 50 crystals of a complex formed between the SRF transcription factor, its cognate DNA, and a peptide from the SRF cofactor MRTF-A. This structure is currently in the process of being fully solved. While full details of the structure are not yet available, the repeated application of BLEND on data from this structure, as they have become available, has made it possible to produce electron density maps clear enough to visualise the potential location of MRTF sequences. Full article
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Open AccessArticle Dislocation Creep: Climb and Glide in the Lattice Continuum
Crystals 2017, 7(8), 243; doi:10.3390/cryst7080243
Received: 9 June 2017 / Revised: 29 July 2017 / Accepted: 31 July 2017 / Published: 4 August 2017
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Abstract
A continuum theory for high temperature creep of polycrystalline solids is developed. It includes the relevant deformation mechanisms for diffusional and dislocation creep: elasticity with eigenstrains resulting from vacancy diffusion, dislocation climb and glide, and the lattice growth/loss at the boundaries enabled by
[...] Read more.
A continuum theory for high temperature creep of polycrystalline solids is developed. It includes the relevant deformation mechanisms for diffusional and dislocation creep: elasticity with eigenstrains resulting from vacancy diffusion, dislocation climb and glide, and the lattice growth/loss at the boundaries enabled by diffusion. All the deformation mechanisms are described with respect to the crystalline lattice, so that the continuum formulation with lattice motion as the basis is necessary. However, dislocation climb serves as the source sink of lattice sites, so that the resulting continuum has a sink/source of its fundamental component, which is reflected in the continuity equation. Climb as a sink/source also affects the diffusion part of the problem, but the most interesting discovery is the climb-glide interaction. The loss/creation of lattice planes through climb affects the geometric definition of crystallographic slip and necessitates the definition of two slip fields: the true slip and the effective slip. The former is the variable on which the dissipative power is expanded during dislocation glide and is thus, the one that must enter the glide constitutive equations. The latter describes the geometry of the slip affected by climb, and is necessary for kinematic analysis. Full article
(This article belongs to the Special Issue Plasticity of Crystals and Interfaces)
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Open AccessArticle Separating NaCl and AlCl3·6H2O Crystals from Acidic Solution Assisted by the Non-Equilibrium Phase Diagram of AlCl3-NaCl-H2O(-HCl) Salt-Water System at 353.15 K
Crystals 2017, 7(8), 244; doi:10.3390/cryst7080244
Received: 30 June 2017 / Revised: 26 July 2017 / Accepted: 2 August 2017 / Published: 4 August 2017
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Abstract
Extracting AlCl3·6H2O from acid leaching solution through crystallization is one of the key processes to extracting aluminum from fly ash, coal gangue and other industrial solid wastes. However, the obtained products usually have low purity and a key problem
[...] Read more.
Extracting AlCl3·6H2O from acid leaching solution through crystallization is one of the key processes to extracting aluminum from fly ash, coal gangue and other industrial solid wastes. However, the obtained products usually have low purity and a key problem is the lack of accurate data for phase equilibrium. This paper presented the non-equilibrium phase diagrams of AlCl3-NaCl-H2O (HCl) salt-water systems under continuous heating and evaporation conditions, which were the main components of the acid leaching solution obtained through a sodium-assisted activation hydrochloric acid leaching process. The ternary system was of a simple eutonic type under different acidities. There were three crystalline regions; the crystalline regions of AlCl3·6H2O, NaCl and the mixture AlCl3·6H2O/NaCl, respectively. The phase diagram was used to optimize the crystallization process of AlCl3·6H2O and NaCl. A process was designed to evaporate and remove NaCl at the first stage of the evaporation process, and then continue to evaporate and crystallize AlCl3·6H2O after solid-liquid separation. The purities of the final salt products were 99.12% for NaCl and up to 97.35% for AlCl3·6H2O, respectively. Full article
(This article belongs to the Special Issue Solution-Processed Inorganic Functional Crystals)
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Open AccessArticle Precipitant-Free Crystallization of Protein Molecules Induced by Incision on Substrate
Crystals 2017, 7(8), 245; doi:10.3390/cryst7080245
Received: 20 July 2017 / Revised: 1 August 2017 / Accepted: 1 August 2017 / Published: 5 August 2017
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Abstract
Nucleation of protein crystals has been shown to be facilitated by substrates decorated with both nano- to micro-scale hierarchical undulations and spatially varying surface potential. In fact, on such surfaces, several proteins were found to crystallize without having to use any precipitant in
[...] Read more.
Nucleation of protein crystals has been shown to be facilitated by substrates decorated with both nano- to micro-scale hierarchical undulations and spatially varying surface potential. In fact, on such surfaces, several proteins were found to crystallize without having to use any precipitant in contrast to all other homogeneous and heterogeneous systems in which precipitant is an essential ingredient for nucleation. While these surfaces were so patterned whole through the area that was brought in contact with the protein solution, it was not clear exactly to what extent the surfaces were required to be patterned to trigger nucleation without use of any precipitant. Here we show that a simple incision may be enough on an otherwise smooth surface for this purpose. In particular, the substrate used here is a smooth silicone film with its surface plasma oxidized to create a thin crust of silica. An incision is then generated on this surface using a sharp razor blade. The silica crust being brittle leads to random nano-microscopic undulations at the vicinity of the incision. These undulations along with surface charge can induce protein crystal nucleation without precipitant. Full article
(This article belongs to the Special Issue Effects of Confinement and Topography on Crystallization)
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Open AccessArticle Algebraic Theory of Crystal Vibrations: Localization Properties of Wave Functions in Two-Dimensional Lattices
Crystals 2017, 7(8), 246; doi:10.3390/cryst7080246
Received: 14 July 2017 / Revised: 2 August 2017 / Accepted: 3 August 2017 / Published: 7 August 2017
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Abstract
The localization properties of the wave functions of vibrations in two-dimensional (2D) crystals are studied numerically for square and hexagonal lattices within the framework of an algebraic model. The wave functions of 2D lattices have remarkable localization properties, especially at the van Hove
[...] Read more.
The localization properties of the wave functions of vibrations in two-dimensional (2D) crystals are studied numerically for square and hexagonal lattices within the framework of an algebraic model. The wave functions of 2D lattices have remarkable localization properties, especially at the van Hove singularities (vHs). Finite-size sheets with a hexagonal lattice (graphene-like materials), in addition, exhibit at zero energy a localization of the wave functions at zigzag edges, so-called edge states. The striped structure of the wave functions at a vHs is particularly noteworthy. We have investigated its stability and that of the edge states with respect to perturbations in the lattice structure, and the effect of the boundary shape on the localization properties. We find that the stripes disappear instantaneously at the vHs in a square lattice when turning on the perturbation, whereas they broaden but persist at the vHss in a hexagonal lattice. For one of them, they eventually merge into edge states with increasing coupling, which, in contrast to the zero-energy edge states, are localized at armchair edges. The results are corroborated based on participation ratios, obtained under various conditions. Full article
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Open AccessArticle Two Supramolecular Cobalt(II) Complexes: Syntheses, Crystal Structures, Spectroscopic Behaviors, and Counter Anion Effects
Crystals 2017, 7(8), 247; doi:10.3390/cryst7080247
Received: 5 July 2017 / Revised: 26 July 2017 / Accepted: 30 July 2017 / Published: 9 August 2017
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Abstract
Two new Co(II) complexes, [{Co(L)}2{Co(Pic)2(CH3OH)2}] (1) and [{CoL(μ-OAc)}2Co] (2), where H2L = 2,2′-[Ethylenedioxybis(nitrilomethylidyne)]dinaphthol, were designed, synthesized and characterized by elemental analysis, FT-IR spectra, UV-Vis spectra,
[...] Read more.
Two new Co(II) complexes, [{Co(L)}2{Co(Pic)2(CH3OH)2}] (1) and [{CoL(μ-OAc)}2Co] (2), where H2L = 2,2′-[Ethylenedioxybis(nitrilomethylidyne)]dinaphthol, were designed, synthesized and characterized by elemental analysis, FT-IR spectra, UV-Vis spectra, and X-ray crystallography. Complex 1 consists of two [CoL] and one [Co(Pic)2(CH3OH)2] (Pic = picrate) units and in the [CoL] unit, the Co(II) atom is tetra-coordinated with a slightly distorted square-planar geometry. In the [Co(Pic)2(CH3OH)2] unit, the Co(II) atom is hexa-coordinated with a slightly distorted octahedral geometry. Meanwhile in complex 2, two acetate ions coordinate to three Co(II) atoms through Co-O-C-O-Co bridges and four μ-naphthoxo oxygen atoms from two [CoL] units also coordinated to the central Co(II) atom. Thus, complex 2 has two distorted square pyramidal coordination geometries around the terminal Co(II) atom and an octahedral geometry around the central Co(II) atom. The supramolecular structures of complex 1 is a 3D-network supramolecular structure linked by C-H···O hydrogen bonds and π···π stacking interaction, but complex 2 possesses a self-assembled 2D-layer supramolecular structure linked by C-H···π and π···π stacking interactions. The structure determinations show that the coordination anions are important factors influencing the crystalline array. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle Induced Mesocrystal-Formation, Hydrothermal Growth and Magnetic Properties of α-Fe2O3 Nanoparticles in Salt-Rich Aqueous Solutions
Crystals 2017, 7(8), 248; doi:10.3390/cryst7080248
Received: 15 June 2017 / Revised: 19 July 2017 / Accepted: 21 July 2017 / Published: 8 August 2017
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Abstract
Iron oxide nanoparticles are widely prevalent in our aqueous environment (e.g., streams, seawater, hydrothermal vents). Their aggregation and crystal growth depend on their chemical surroundings, for instance just a change in pH or salt concentration can greatly affect this. In turn this influences
[...] Read more.
Iron oxide nanoparticles are widely prevalent in our aqueous environment (e.g., streams, seawater, hydrothermal vents). Their aggregation and crystal growth depend on their chemical surroundings, for instance just a change in pH or salt concentration can greatly affect this. In turn this influences their properties, mobility, fate, and environmental impact. We studied the growth of α-Fe2O3 (hematite), starting from 8 nm hematite particles in weakly acidic (HNO3) aqueous suspension with different states of particle aggregation, using salt (NaCl and NaH2PO4) to control their initial aggregation state. The samples were then subject to hydrothermal treatment at 100–140 °C. We followed the development in aggregation state and particle size by dynamic light scattering, X-ray diffraction, small angle neutron scattering and transmission electron microscopy, and the magnetic properties by Mössbauer spectroscopy. The addition of NaCl and NaH2PO4 both led to aggregation, but NaCl led to linear chains of hematite nanoparticles (oriented parallel to their hexagonal c-axis), such that the crystalline lattice planes of neighboring hematite particles were aligned. However, despite this oriented alignment, the particles did not merge and coalesce. Rather they remained stable as mesocrystals until heat-treated. In turn, the addition of NaCl significantly increases the rate of growth during hydrothermal treatment, probably because the nanoparticles, due to the chain formation, are already aligned and in close proximity. With hydrothermal treatment, the magnetic properties of the particles transform from those characteristic of small (aggregated) hematite nanoparticles to those of particles with more bulk-like properties such as Morin transition and suppression of superparamagnetic relaxation, in correspondence with the growth of particle size. Full article
(This article belongs to the Special Issue Mesocrystals and Hierarchical Structures)
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Open AccessArticle Crystal Growth and Luminescence Properties of Dy3+ and Ge4+ Co-Doped Bi4Si3O12 Single Crystals for High Power Warm White LED
Crystals 2017, 7(8), 249; doi:10.3390/cryst7080249
Received: 14 July 2017 / Revised: 4 August 2017 / Accepted: 7 August 2017 / Published: 9 August 2017
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Abstract
Φ1 inch Dy3+ and Ge4+ co-doped bismuth silicate (Bi4Si3O12, BSO) single crystals with the length of 80–100 mm were successfully grown by Bridgman method. They are transparent, free of cracks and inclusions. The white residual
[...] Read more.
Φ1 inch Dy3+ and Ge4+ co-doped bismuth silicate (Bi4Si3O12, BSO) single crystals with the length of 80–100 mm were successfully grown by Bridgman method. They are transparent, free of cracks and inclusions. The white residual at the top parts of BSO crystals disappears with co-doping 1 mol% Dy3+ and more than 3 mol% Ge4+. The FWHM values of X-ray rocking curves shows 1%Dy,3%Ge:BSO crystal possesses high crystallization quality. The intrinsic emission peak of BSO and the characteristic emission peaks of Dy3+ ions are weakened with increasing the doping concentration of Ge4+. 1 mol% Dy3+ and 3 mol% Ge4+ are the optimal concentrations due to high crystallization quality and moderate emission intensity. The CIE coordinates and CCT values shift towards warmer white light region with increased Ge4+ co-doping. The CCT values are close to the ideal value of 3000 K for warm white light when 1%Dy,3%Ge:BSO crystal is excited by various UV light. Increasing the temperature from 298 K to 573 K leads the luminescence lifetime to decrease from 659 μs to 645 μs. More than 95% and 80% photoluminescence intensity at room temperature is still retained at 423 K and 573 K respectively. Dy,Ge:BSO crystals are potential candidates for fabricating high power warm WLEDs. Full article
(This article belongs to the Special Issue Luminescent Properties of Lanthanoid Doped Crystals)
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Open AccessArticle Simulation Model Development for Packaged Cascode Gallium Nitride Field-Effect Transistors
Crystals 2017, 7(8), 250; doi:10.3390/cryst7080250
Received: 24 June 2017 / Revised: 4 August 2017 / Accepted: 6 August 2017 / Published: 9 August 2017
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Abstract
This paper presents a simple behavioral model with experimentally extracted parameters for packaged cascode gallium nitride (GaN) field-effect transistors (FETs). This study combined a level-1 metal–oxide–semiconductor field-effect transistor (MOSFET), a junction field-effect transistor (JFET), and a diode model to simulate a cascode GaN
[...] Read more.
This paper presents a simple behavioral model with experimentally extracted parameters for packaged cascode gallium nitride (GaN) field-effect transistors (FETs). This study combined a level-1 metal–oxide–semiconductor field-effect transistor (MOSFET), a junction field-effect transistor (JFET), and a diode model to simulate a cascode GaN FET, in which a JFET was used to simulate a metal-insulator-semiconductor high-electron-mobility transistor (MIS-HEMT). Using the JFET to simulate the MIS-HEMT not only ensures that the curve fits an S-shape transfer characteristic but also enables the pinch-off voltages extracted from the threshold voltage of the MIS-HEMT to be used as a watershed to distinguish where the drop in parasitic capacitance occurs. Parameter extraction was based on static and dynamic characteristics, which involved simulating the behavior of the created GaN FET model and comparing the extracted parameters with experimental measurements to demonstrate the accuracy of the simulation program with an integrated circuit emphasis (SPICE) model. Cascode capacitance was analyzed and verified through experimental measurements and SPICE simulations. The analysis revealed that the capacitance of low-voltage MOSFETs plays a critical role in increasing the overall capacitance of cascode GaN FETs. The turn-off resistance mechanism effectively described the leakage current, and a double-pulse tester was used to evaluate the switching performance of the fabricated cascode GaN FET. LTspice simulation software was adopted to compare the experimental switching results. Overall, the simulation results were strongly in agreement with the experimental results. Full article
(This article belongs to the Special Issue Advances in GaN Crystals and Their Applications)
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Open AccessArticle Synthesis of Two Novels-Shaped Dibenzo[c,l] Chrysene Derivatives, Crystal Structure, and the Evaluation of their Photophysical Properties
Crystals 2017, 7(8), 251; doi:10.3390/cryst7080251
Received: 12 July 2017 / Revised: 8 August 2017 / Accepted: 8 August 2017 / Published: 9 August 2017
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Abstract
Two s-shaped polyaromatic dibenzo[c,l]chrysene derivatives have been synthesized by a two-step process, via. The Wittig reaction, followed by iodine, promoted photocyclization. These molecules have been characterized by 1H NMR, FAB-MS, and elemental analysis. Further, the molecular structures of 4a and 4b have
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Two s-shaped polyaromatic dibenzo[c,l]chrysene derivatives have been synthesized by a two-step process, via. The Wittig reaction, followed by iodine, promoted photocyclization. These molecules have been characterized by 1H NMR, FAB-MS, and elemental analysis. Further, the molecular structures of 4a and 4b have been confirmed by single crystal X-ray diffraction analysis. The protons located in the cove-regions of molecules 4a and 4b showed downfield shifts of the protons. Molecule 4a crystallized under the monoclinic system with space group C2/c, and the molecule 4b crystallized under the monoclinic system with space group P21/n. Molecules 4a and 4b showed strong absorption maxima wavelengths at 310 nm and 324 nm, respectively. The molar extinctinction coefficients (ε) of the compounds 4a and 4b indicated that molecule 4b has a better ability to absorb UV light than molecule 4a. The emission spectra of the molecules 4a and 4b displayed peaks in the region 429–456 nm. The shape of the UV-Visible and Fluorescence spectra of the molecules 4a and 4b look almost identical. However, molecule 4b exhibited better fluorescence intensity than molecule 4a. This may be due to the difference in the substituents of molecules 4a and 4b. Full article
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Open AccessArticle Interfacial Kinetics of Efficient Perovskite Solar Cells
Crystals 2017, 7(8), 252; doi:10.3390/cryst7080252
Received: 9 June 2017 / Revised: 30 July 2017 / Accepted: 3 August 2017 / Published: 13 August 2017
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Abstract
Perovskite solar cells (PSCs) have immense potential for high power conversion efficiency with an ease of fabrication procedure. The fundamental understanding of interfacial kinetics in PSCs is crucial for further improving of their photovoltaic performance. Herein we use the current-voltage (J-V)
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Perovskite solar cells (PSCs) have immense potential for high power conversion efficiency with an ease of fabrication procedure. The fundamental understanding of interfacial kinetics in PSCs is crucial for further improving of their photovoltaic performance. Herein we use the current-voltage (J-V) characteristics and impedance spectroscopy (IS) measurements to probe the interfacial kinetics on efficient MAPbI3 solar cells. We show that series resistance (RS) of PSCs exhibits an ohmic and non-ohmic behavior that causes a significant voltage drop across it. The Nyquist spectra as a function of applied bias reveal the characteristic features of ion motion and accumulation that is mainly associated with the MA cations in MAPbI3. With these findings, we provide an efficient way to understand the working mechanism of perovskite solar cells. Full article
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Open AccessArticle Mechanical Anisotropy in Austenitic NiMnGa Alloy: Nanoindentation Studies
Crystals 2017, 7(8), 254; doi:10.3390/cryst7080254
Received: 23 June 2017 / Revised: 14 August 2017 / Accepted: 15 August 2017 / Published: 17 August 2017
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Abstract
Abstract: Mechanical anisotropy in an austenitic ferromagnetic shape memory alloy (SMA), Ni50Mn26.25Ga23.75, is investigated along (010), (120), (121), (231) and (232) using nanoindentation. While (010) exhibits the highest reduced modulus, Er, and hardness, H
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Abstract: Mechanical anisotropy in an austenitic ferromagnetic shape memory alloy (SMA), Ni50Mn26.25Ga23.75, is investigated along (010), (120), (121), (231) and (232) using nanoindentation. While (010) exhibits the highest reduced modulus, Er, and hardness, H, (232) shows the lowest amongst the grain orientations examined in this study. The significant elastic anisotropy measured is attributed to differences in planar packing density and number of in-plane Ni–Mn and Ni–Ga bonds, whereas the plastic anisotropy is due to the differences in the onset of slip, which is rationalized by recourse to Schmid factor calculations. This would help determine the grain orientations in austenitic NiMnGa which exhibit better mechanical properties for SMA applications such as improving vibration damping characteristics of the alloy. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness)
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Open AccessArticle Evaluation of Thin Copper Wire and Lead-Free Solder Joint Strength by Pullout Tests and Wire Surface Observation
Crystals 2017, 7(8), 255; doi:10.3390/cryst7080255
Received: 13 July 2017 / Revised: 13 August 2017 / Accepted: 18 August 2017 / Published: 20 August 2017
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Abstract
Copper wires have been attracting much attention for Large Scale Integration (LSI) bonding because of their excellent mechanical and electrical properties, in addition to their low material cost. The ends of these wires are usually joined to pads or through-holes on a printed
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Copper wires have been attracting much attention for Large Scale Integration (LSI) bonding because of their excellent mechanical and electrical properties, in addition to their low material cost. The ends of these wires are usually joined to pads or through-holes on a printed circuit board, and lead-free soldering is one of the popular bonding methods. Since the deformation resistance of solder is lower than that of copper, especially in slow deformation due to creep, the strain tends to be increased in the solder and concentrated near the copper/solder joint interface. Thus, fracture frequently occurs at this interface and may influence the quality of the product. It is therefore important to evaluate the bonding strength of thin copper wire and lead-free solder. In this paper, pullout tests of thin copper wire from lead-free solder were carried out, and the pullout behavior of the wires was observed. The bonding strength was evaluated based on the actual bonded area on the copper wire surface. Finally, the strength of the thin copper wire/solder joint was summarized using the shear and tensile strengths of the copper/solder interface as well as the tensile strength of the copper wire. Full article
(This article belongs to the Special Issue Advance in Crystalline Thin Wires)
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Review

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Open AccessReview Light-Triggered Formation of Surface Topographies in Azo Polymers
Crystals 2017, 7(8), 231; doi:10.3390/cryst7080231
Received: 5 July 2017 / Revised: 20 July 2017 / Accepted: 22 July 2017 / Published: 26 July 2017
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Abstract
Properties such as friction, wettability and visual impact of polymer coatings are influenced by the surface topography. Therefore, control of the surface structure is of eminent importance to tuning its function. Photochromic azobenzene-containing polymers are an appealing class of coatings of which the
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Properties such as friction, wettability and visual impact of polymer coatings are influenced by the surface topography. Therefore, control of the surface structure is of eminent importance to tuning its function. Photochromic azobenzene-containing polymers are an appealing class of coatings of which the surface topography is controllable by light. The topographies form without the use of a solvent, and can be designed to remain static or have dynamic properties, that is, be capable of reversibly switching between different states. The topographical changes can be induced by using linear azo polymers to produce surface-relief gratings. With the ability to address specific regions, interference patterns can imprint a variety of structures. These topographies can be used for nanopatterning, lithography or diffractive optics. For cross-linked polymer networks containing azobenzene moieties, the coatings can form topographies that disappear as soon as the light trigger is switched off. This allows the use of topography-forming coatings in a wide range of applications, ranging from optics to self-cleaning, robotics or haptics. Full article
(This article belongs to the Section Liquid Crystals)
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Open AccessReview Ferroelectricity in Simple Binary Crystals
Crystals 2017, 7(8), 232; doi:10.3390/cryst7080232
Received: 28 April 2017 / Revised: 22 May 2017 / Accepted: 23 May 2017 / Published: 28 July 2017
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Abstract
The origin of ferroelectricity in doped binary crystals, Pb1−xGexTe, Cd1−xZnxTe, Zn1−xLixO, and Hf1−xZrxO2 is discussed, while no binary ferroelectrics have been reported
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The origin of ferroelectricity in doped binary crystals, Pb1−xGexTe, Cd1−xZnxTe, Zn1−xLixO, and Hf1−xZrxO2 is discussed, while no binary ferroelectrics have been reported except for two crystals, HCl and HBr. The ferroelectricity is induced only in doped crystals, which shows an importance of electronic modification in chemical bonds by dopants. The phenomenological and microscopic treatments are given for the appearance of ferroelectric activity. The discovery of ferroelectricity in binary crystals such as ZnO and HfO2 is of high interest in fundamental science and also in application for complementary metal–oxide semiconductor (CMOS) technology. Full article
(This article belongs to the Special Issue Crystal Structure of Electroceramics)
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Open AccessFeature PaperReview What Can We Learn from the Crystal Structures of Metallacarboranes?
Crystals 2017, 7(8), 234; doi:10.3390/cryst7080234
Received: 26 June 2017 / Revised: 25 July 2017 / Accepted: 25 July 2017 / Published: 29 July 2017
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Abstract
The determination of the molecular structures of metallacarboranes by X-ray diffraction remains critical to the development of the field, in some cases being the only viable way in which the overall architecture and the isomeric form of the molecule can be established. In
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The determination of the molecular structures of metallacarboranes by X-ray diffraction remains critical to the development of the field, in some cases being the only viable way in which the overall architecture and the isomeric form of the molecule can be established. In such studies one problem frequently met is how to distinguish correctly {BH} and {CH} vertices, and this review begins by describing two relatively new methods, the Vertex-Centroid Distance (VCD) and Boron-Hydrogen Distance (BHD) methods, that have been developed to overcome the problem. Once the cage C atoms are located correctly, the resulting metallacarborane structure can frequently be analysed on the basis that cage B has a greater Structural Trans Effect (STE) than does cage C. In the absence of significant competing effects this gives rise to unequal M–L distances for a homogeneous ligand set and to a preferred Exopolyhedral Ligand Orientation (ELO) for a heterogeneous ligand set. ELO considerations can be used, amongst other things, to rank order the STEs of ligands and to identify suspect (in terms of cage C atom positions) metallacarborane structures. Full article
(This article belongs to the Special Issue Crystal Structures of Boron Compounds)
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Open AccessReview Incorporation of Large Impurity Atoms into the Diamond Crystal Lattice: EPR of Split-Vacancy Defects in Diamond
Crystals 2017, 7(8), 237; doi:10.3390/cryst7080237
Received: 27 June 2017 / Revised: 27 July 2017 / Accepted: 28 July 2017 / Published: 31 July 2017
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Abstract
Diamond is a unique mineral widely used in diverse fields due to its remarkable properties. The development of synthesis technology made it possible to create diamond-based semiconductor devices. In addition, doped diamond can be used as single photon emitters in various luminescence applications.
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Diamond is a unique mineral widely used in diverse fields due to its remarkable properties. The development of synthesis technology made it possible to create diamond-based semiconductor devices. In addition, doped diamond can be used as single photon emitters in various luminescence applications. Different properties are the result of the presence of impurities or intrinsic defects in diamond. Thus, the investigation of the defect formation process is of particular interest. Although hydrogen, nitrogen, and boron have been known to form different point defects, the possibility for large impurity atoms to incorporate into the diamond crystal structure has been questioned for a long time. In the current paper, the paramagnetic nickel split-vacancy defect in diamond is described, and the further investigation of nickel-, cobalt-, titanium-, phosphorus-, silicon-, and germanium-related defects is discussed. Full article
(This article belongs to the Special Issue Diamond Crystals)
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Open AccessReview Organization of Twisting Lamellar Crystals in Birefringent Banded Polymer Spherulites: A Mini-Review
Crystals 2017, 7(8), 241; doi:10.3390/cryst7080241
Received: 12 July 2017 / Revised: 2 August 2017 / Accepted: 2 August 2017 / Published: 4 August 2017
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Abstract
In this mini-review, we summarize the evidences of lamellar twisting in the birefringent banded polymer spherulites demonstrated by various characterization techniques, such as polarized optical microscopy, real-time atomic force microscopy, micro-focus wide angle X-ray diffraction, etc. The real-time observation of lamellar growth under
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In this mini-review, we summarize the evidences of lamellar twisting in the birefringent banded polymer spherulites demonstrated by various characterization techniques, such as polarized optical microscopy, real-time atomic force microscopy, micro-focus wide angle X-ray diffraction, etc. The real-time observation of lamellar growth under atomic force microscopy unveiled the fine details of lamellar twisting and branching in the banded spherulites of poly(R-3-hydroxybutyrate-co-17 mol% R-3-hydroxyhexanoate). Organization of the twisting lamellar crystals in the banded spherulites was revealed as well. The lamellar crystals change the orientation via twisting rather than the macro screw dislocations. In fact, macro screw dislocation provides the mechanism of synchronous twisting of neighboring lamellar crystals. The driving force of lamellar twisting is attributed to the anisotropic and unbalanced surface stresses. Besides molecular chirality, variation of the growth axis and the chemical groups on lamellar surface can change the distribution of the surface stresses, and thus may invert the handedness of lamellar twisting. Thus, based on both experimental results and physical reasoning, the relation between crystal chirality and chemical molecular structures has been suggested, via the bridge of the distribution of surface stresses. The factors affecting band spacing are briefly discussed. Some remaining questions and the perspective of the topic are highlighted. Full article
(This article belongs to the Special Issue Crystal Morphology and Assembly in Spherulites)
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Open AccessReview Structural Basis of DEAH/RHA Helicase Activity
Crystals 2017, 7(8), 253; doi:10.3390/cryst7080253
Received: 6 July 2017 / Revised: 12 August 2017 / Accepted: 13 August 2017 / Published: 15 August 2017
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Abstract
DEAH/RHA helicases are members of a large group of proteins collectively termed DExH-box, which also include Ski2-like and NS3/NPH-II helicases. By binding and remodeling DNA and RNA, DEAH/RHA helicases play critical roles in many cellular processes ranging from transcription and splicing to ribosome
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DEAH/RHA helicases are members of a large group of proteins collectively termed DExH-box, which also include Ski2-like and NS3/NPH-II helicases. By binding and remodeling DNA and RNA, DEAH/RHA helicases play critical roles in many cellular processes ranging from transcription and splicing to ribosome biogenesis, innate immunity and stress granule formation. While numerous crystal structures of other DExH-box proteins helicases have been reported, no structures of DEAH/RHA helicases bound to nucleic acid substrates have been available until the recent co-crystal structures of the maleless (MLE) and Prp43p bound to RNA. This review examines how these new structures provide a starting point to understand how DEAH/RHA helicases bind to, translocate on, and unwind nucleic acid substrates. Full article
(This article belongs to the Special Issue Nucleic Acid Crystallography)
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