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Crystals, Volume 7, Issue 6 (June 2017)

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Cover Story (view full-size image) Ordered shells might be instrumental in the realization of scaled crystals. The shells are expected [...] Read more.
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Open AccessLetter Switchable Two-Dimensional Liquid Crystal Grating in Blue Phase
Crystals 2017, 7(6), 182; https://doi.org/10.3390/cryst7060182
Received: 11 May 2017 / Revised: 18 June 2017 / Accepted: 19 June 2017 / Published: 21 June 2017
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Abstract
We demonstrate a switchable two-dimensional phase grating in blue phase liquid crystal (BPLC), which is fabricated by sawtooth in-plane-switch (IPS) electrodes. They are used to generate the horizontal electric field on a single indium-tin-oxide (ITO) glass substrate and, as a result, the 1-D
[...] Read more.
We demonstrate a switchable two-dimensional phase grating in blue phase liquid crystal (BPLC), which is fabricated by sawtooth in-plane-switch (IPS) electrodes. They are used to generate the horizontal electric field on a single indium-tin-oxide (ITO) glass substrate and, as a result, the 1-D and 2-D phase gratings can be mutual switched via different polarizations of incident light with an applied voltage. The first-order diffraction efficiency is up to 20% and 10% for the 1-D and 2-D phase grating at V = 150 V, respectively. Moreover, the rise and decay time is 0.9 and 1.1 ms, respectively, which is suitable for wide applications of high-speed optical manipulations. Full article
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Open AccessArticle Combining Single- and Poly-Crystalline Measurements for Identification of Crystal Plasticity Parameters: Application to Austenitic Stainless Steel
Crystals 2017, 7(6), 181; https://doi.org/10.3390/cryst7060181
Received: 24 April 2017 / Revised: 12 June 2017 / Accepted: 16 June 2017 / Published: 21 June 2017
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Abstract
Crystal plasticity finite element models have been extensively used to simulate various aspects of polycrystalline deformations. A common weakness of practically all models lies in a relatively large number of constitutive modeling parameters that, in principle, would require dedicated measurements on proper length
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Crystal plasticity finite element models have been extensively used to simulate various aspects of polycrystalline deformations. A common weakness of practically all models lies in a relatively large number of constitutive modeling parameters that, in principle, would require dedicated measurements on proper length scales in order to perform reliable model calibration. It is important to realize that the obtained data at different scales should be properly accounted for in the models. In this work, a two-scale calibration procedure is proposed to identify (conventional) crystal plasticity model parameters on a grain scale from tensile test experiments performed on both single crystals and polycrystals. The need for proper adjustment of the polycrystalline tensile data is emphasized and demonstrated by subtracting the length scale effect, originating due to grain boundary strengthening, following the Hall–Petch relation. A small but representative volume element model of the microstructure is identified for fast and reliable identification of modeling parameters. Finally, a simple hardening model upgrade is proposed to incorporate the grain size effects in conventional crystal plasticity. The calibration strategy is demonstrated on tensile test measurements on 316L austenitic stainless steel obtained from the literature. Full article
(This article belongs to the Special Issue Plasticity of Crystals and Interfaces)
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Open AccessArticle Microstructure Analysis and Thermoelectric Properties of Melt-Spun Bi-Sb-Te Compounds
Crystals 2017, 7(6), 180; https://doi.org/10.3390/cryst7060180
Received: 25 May 2017 / Revised: 19 June 2017 / Accepted: 19 June 2017 / Published: 20 June 2017
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Abstract
In order to realize high-performance thermoelectric materials, a way to obtain small grain size is necessary for intensification of the phonon scattering. Here, we use a melt-spinning-spark plasma sintering process for making p-type Bi0.36Sb1.64Te3 thermoelectric materials and evaluate
[...] Read more.
In order to realize high-performance thermoelectric materials, a way to obtain small grain size is necessary for intensification of the phonon scattering. Here, we use a melt-spinning-spark plasma sintering process for making p-type Bi0.36Sb1.64Te3 thermoelectric materials and evaluate the relation between the process conditions and thermoelectric performance. We vary the Cu wheel rotation speed from 1000 rpm (~13 ms−1) to 4000 rpm (~52 ms−1) during the melt spinning process to change the cooling rate, allowing us to control the characteristic size of nanostructure in melt-spun Bi0.36Sb1.64Te3 ribbons. The higher wheel rotation speed decreases the size of nanostructure, but the grain sizes of sintered pellets are inversely proportional to the nanostructure size after the same sintering condition. As a result, the ZT values of the bulks fabricated from 1000–3000 rpm melt-spun ribbons are comparable each other, while the ZT value of the bulk from the 4000 rpm melt-spun ribbons is rather lower due to reduction of grain boundary phonon scattering. In this work, we can conclude that the smaller nanostructure in the melt spinning process does not always guarantee high-performance thermoelectric bulks, and an adequate following sintering process must be included. Full article
(This article belongs to the Special Issue Materials Processing and Crystal Growth for Thermoelectrics)
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Open AccessArticle Crystal Growth of High-Quality Protein Crystals under the Presence of an Alternant Electric Field in Pulse-Wave Mode, and a Strong Magnetic Field with Radio Frequency Pulses Characterized by X-ray Diffraction
Crystals 2017, 7(6), 179; https://doi.org/10.3390/cryst7060179
Received: 29 April 2017 / Revised: 12 June 2017 / Accepted: 15 June 2017 / Published: 19 June 2017
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Abstract
The first part of this research was devoted to investigating the effect of alternate current (AC) using four different types of wave modes (pulse-wave) at 2 Hz on the crystal growth of lysozyme in solution. The best results, in terms of size and
[...] Read more.
The first part of this research was devoted to investigating the effect of alternate current (AC) using four different types of wave modes (pulse-wave) at 2 Hz on the crystal growth of lysozyme in solution. The best results, in terms of size and crystal quality, were obtained when protein crystals were grown under the influence of electric fields in a very specific wave mode (“breathing” wave), giving the highest resolution up to 1.34 Å in X-ray diffraction analysis compared with controls and with those crystals grown in gel. In the second part, we evaluated the effect of a strong magnetic field of 16.5 Tesla combined with radiofrequency pulses of 0.43 μs on the crystal growth in gels of tetragonal hen egg white (HEW) lysozyme. The lysozyme crystals grown, both in solution applying breathing-wave and in gel under the influence of this strong magnetic field with pulses of radio frequencies, produced the larger-in-size crystals and the highest resolution structures. Data processing and refinement statistics are very good in terms of the resolution, mosaicity and Wilson B factor obtained for each crystal. Besides, electron density maps show well-defined and distinctly separated atoms at several selected tryptophan residues for the crystal grown using the “breathing wave pulses”. Full article
(This article belongs to the Special Issue Protein Crystallization under the Presence of an Electric Field)
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Open AccessReview Heteroepitaxy, an Amazing Contribution of Crystal Growth to the World of Optics and Electronics
Crystals 2017, 7(6), 178; https://doi.org/10.3390/cryst7060178
Received: 21 April 2017 / Revised: 5 June 2017 / Accepted: 11 June 2017 / Published: 19 June 2017
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Abstract
Advances in Electronics and Optics are often preceded by discoveries in Crystal Growth theory and practice. This article represents in retrospect some of the most significant contributions of heteroepitaxy in these and some other areas—the strong impact of the three modes of heteroepitaxy
[...] Read more.
Advances in Electronics and Optics are often preceded by discoveries in Crystal Growth theory and practice. This article represents in retrospect some of the most significant contributions of heteroepitaxy in these and some other areas—the strong impact of the three modes of heteroepitaxy on microelectronics and quantum optics, the big “push” of PENDEO epitaxy in development of Light Emitting Diodes, etc. A large part of the text is dedicated to heteroepitaxy of nonlinear optical materials grown on orientation-patterned templates and used in the development of new quasi-phase-matching frequency conversion laser sources. By achieving new frequency ranges such sources will result in a wide variety of applications in areas such as defense, security, industry, medicine, and science. Interesting facts from the scientific life of major contributors in the field are mixed in the text with fine details from growth experiments, chemical equations, results from material characterizations and some optical and crystallographic considerations—all these presented in a popular way but without neglecting their scientific importance and depth. The truth is that often heteroepitaxy is not just the better but the only available option. The truth is that delays in device development are usually due to gaps in materials research. In all this, miscommunication between different scientific communities always costs vain efforts, uncertainty, and years of going in a wrong scientific direction. With this article we aim to stimulate a constructive dialog that could lead to solutions of important interdisciplinary scientific and technical issues. Full article
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Open AccessArticle The Role of III-V Substrate Roughness and Deoxidation Induced by Digital Etch in Achieving Low Resistance Metal Contacts
Crystals 2017, 7(6), 177; https://doi.org/10.3390/cryst7060177
Received: 2 May 2017 / Revised: 2 June 2017 / Accepted: 13 June 2017 / Published: 19 June 2017
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Abstract
To achieve low contact resistance between metal and III-V material, transmission-line-model (TLM) structures of molybdenum (Mo) were fabricated on indium phosphide (InP) substrate on the top of an indium gallium arsenide (InGaAs) layer grown by molecular beam epitaxy. The contact layer was prepared
[...] Read more.
To achieve low contact resistance between metal and III-V material, transmission-line-model (TLM) structures of molybdenum (Mo) were fabricated on indium phosphide (InP) substrate on the top of an indium gallium arsenide (InGaAs) layer grown by molecular beam epitaxy. The contact layer was prepared using a digital etch procedure before metal deposition. The contact resistivity was found to decrease significantly with the cleaning process. High Resolution Transmission & Scanning Electron Microscopy (HRTEM & HRSTEM) investigations revealed that the surface roughness of treated samples was increased. Further analysis of the metal-semiconductor interface using Energy Electron Loss Spectroscopy (EELS) showed that the amount of oxides (InxOy, GaxOy or AsxOy) was significantly decreased for the etched samples. These results suggest that the low contact resistance obtained after digital etching is attributed to the combined effects of the induced surface roughness and oxides removal during the digital etch process. Full article
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Open AccessArticle Synthesis and Characterization of a New Cobaloxime-Terpyridine Compound
Crystals 2017, 7(6), 175; https://doi.org/10.3390/cryst7060175
Received: 6 March 2017 / Revised: 7 June 2017 / Accepted: 13 June 2017 / Published: 19 June 2017
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Abstract
A new cobaloxime was synthesized by the reaction of cobalt chloride and diphenylglyoxime in methanol, followed by the addition of 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine, pytpy. This complex was characterized by UV–Vis spectroscopy, 1H-NMR spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction analysis. In cyclic voltammetry experiments
[...] Read more.
A new cobaloxime was synthesized by the reaction of cobalt chloride and diphenylglyoxime in methanol, followed by the addition of 4′-(4-pyridyl)-2,2′:6′,2′′-terpyridine, pytpy. This complex was characterized by UV–Vis spectroscopy, 1H-NMR spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction analysis. In cyclic voltammetry experiments an irreversible reduction wave assigned to Co(III)/Co(II) at Ecp = −0.31 V vs. Ag/AgCl and a quasi-reversible process assigned to the Co(II)/Co(I) reduction at −0.72 V vs. Ag/AgCl were observed. The crystal of the complex belongs to the triclinic space group P1 with a = 12.4698(6) Å, b = 14.1285(8) Å, c = 15.5801(8) Å, α = 109.681(4)°, β = 112.975(4)°, γ = 81.67(96.414(4)°3)°, V = 2284.0(2) Å3, Z = 2, Dc = 1.408 mg·m−3, μ = 0.66 mm−1, F(000) = 996, and final R1 = 0.0564, ωR2 = 0.1502. Full article
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Open AccessArticle Theoretical Study on Electronic, Optical Properties and Hardness of Technetium Phosphides under High Pressure
Crystals 2017, 7(6), 176; https://doi.org/10.3390/cryst7060176
Received: 4 April 2017 / Revised: 18 May 2017 / Accepted: 15 June 2017 / Published: 18 June 2017
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Abstract
In this paper, the structural properties of technetium phosphides Tc3P and TcP4 are investigated by first principles at zero pressure and compared with the experimental values. In addition, the electronic properties of these two crystals in the pressure range of
[...] Read more.
In this paper, the structural properties of technetium phosphides Tc3P and TcP4 are investigated by first principles at zero pressure and compared with the experimental values. In addition, the electronic properties of these two crystals in the pressure range of 0–40 GPa are investigated. Further, we discuss the change in the optical properties of technetium phosphides at high pressures. At the end of our study, we focus on the research of the hardness of TcP4 at different pressures by employing a semiempirical method, and the effect of pressure on the hardness is studied. Results show that the hardness of TcP4 increases with the increasing pressure, and the influence mechanism of pressure effect on the hardness of TcP4 is also discussed. Full article
(This article belongs to the Special Issue Crystal Indentation Hardness) Printed Edition available
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Open AccessArticle Evolution in Time of Radiation Defects Induced by Negative Pions and Muons in Crystals with a Diamond Structure
Crystals 2017, 7(6), 174; https://doi.org/10.3390/cryst7060174
Received: 27 March 2017 / Revised: 29 May 2017 / Accepted: 9 June 2017 / Published: 14 June 2017
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Abstract
Evolution in time of radiation defects induced by negatively-charged pions and muons in crystals with diamond structures is considered. Negative pions and muons are captured by the nucleus and ionize an appropriate host atom, forming a positively-charged radiation defect in a lattice. As
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Evolution in time of radiation defects induced by negatively-charged pions and muons in crystals with diamond structures is considered. Negative pions and muons are captured by the nucleus and ionize an appropriate host atom, forming a positively-charged radiation defect in a lattice. As a result of an evolution in time, this radiation defect transforms into the acceptor center. An analysis of the full evolution process is considered for the first time. Formation of this acceptor center can be divided into three stages. At the first stage, the radiation defect interacts with a radiation trace and captures electrons. The radiation defect is neutralized completely in Si and Ge for a short time t 10 11 s, but in diamond, the complete neutralization time is very large t 10 6 s. At the second stage, broken chemical bonds of the radiation defect are restored. In Si and Ge, this process takes place for the neutral radiation defect, but in diamond, it goes for a positively-charged state. The characteristic time of this stage is t < 10 8 s for Si and Ge and t < 10 11 s for diamond. After the chemical bonds’ restoration, the positively-charged, but chemically-bound radiation defect in diamond is quickly neutralized because of the electron density redistribution. The neutralization process is characterized by the lattice relaxation time. At the third stage, a neutral chemically-bound radiation defect captures an additional electron to saturate all chemical bonds and forms an ionized acceptor center. The existence of a sufficiently big electric dipolar moment leads to the electron capture. Qualitative estimates for the time of this process were obtained for diamond, silicon and germanium crystals. It was sown that this time is the shortest for diamond (≤ 10 8 s) and the longest for silicon (≤ 10 7 s) Full article
(This article belongs to the Special Issue Diamond Crystals)
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Open AccessArticle First Principles Study on Structure Stability and Mechanical Properties of YNi2B2C and LuNi2B2C under Pressure
Crystals 2017, 7(6), 173; https://doi.org/10.3390/cryst7060173
Received: 20 April 2017 / Revised: 16 May 2017 / Accepted: 28 May 2017 / Published: 13 June 2017
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Abstract
The pressure effects on the lattice parameters and elastic constants of the tetragonal RNi2B2C (R=Y, Lu) are investigated by means of the first principles. The predicted lattice constants and elastic constants of YNi2B2C and LuNi
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The pressure effects on the lattice parameters and elastic constants of the tetragonal RNi 2 B 2 C (R=Y, Lu) are investigated by means of the first principles. The predicted lattice constants and elastic constants of YNi 2 B 2 C and LuNi 2 B 2 C at 0 GPa agree well with the available data. By the elastic stability criteria under isotropic pressure, it is predicted that YNi 2 B 2 C and LuNi 2 B 2 C with tetragonal structure are not mechanically stable above 93 GPa and 50 GPa, respectively. Pugh’s modulus ratio, Poisson’s ratio, Vickers hardness, elastic anisotropy and Debye temperature of YNi 2 B 2 C in the pressure range of 0–100 GPa and LuNi 2 B 2 C in the pressure range of 0-60 GPa are further investigated. It is shown that the ductility and Debye temperature of tetragonal RNi 2 B 2 C (R=Y, Lu) increase with increasing pressure, and LuNi 2 B 2 C is more ductile and lower Debye temperature than YNi 2 B 2 C under different pressures. Full article
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Open AccessArticle Structural and Electrical Properties Characterization of Sb1.52Bi0.48Te3.0 Melt-Spun Ribbons
Crystals 2017, 7(6), 172; https://doi.org/10.3390/cryst7060172
Received: 28 April 2017 / Revised: 1 June 2017 / Accepted: 7 June 2017 / Published: 13 June 2017
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Abstract
Melt-spinning (MS) has been reported as a promising tool to tailor the microstructure of bulk thermoelectric materials leading to enhanced thermoelectric performances. Here, we report on a detailed characterization of p-type Bi0.48Sb1.52Te3 ribbons produced by melt-spinning. The
[...] Read more.
Melt-spinning (MS) has been reported as a promising tool to tailor the microstructure of bulk thermoelectric materials leading to enhanced thermoelectric performances. Here, we report on a detailed characterization of p-type Bi0.48Sb1.52Te3 ribbons produced by melt-spinning. The microstructure of the melt-spun ribbons has been studied by means of X-ray diffraction, scanning and transmission electron microscopy (TEM). The analyses indicate that the ribbons are highly-textured with a very good chemical homogeneity. TEM reveals clear differences in the microstructure at large and short-range scales between the surface that was in contact with the copper wheel and the free surface. These analyses further evidence the absence of amorphous regions in the melt-spun ribbons and the precipitation of elemental Te at the grain boundaries. Low-temperature electrical resistivity and thermopower measurements (20–300 K) carried out on several randomly-selected ribbons confirm the excellent reproducibility of the MS process. However, the comparison of the transport properties of the ribbons with those of bulk polycrystalline samples of the same initial composition shows that MS leads to a more pronounced metallic character. This difference is likely tied to changes in deviations from stoichiometry due to the out-of-equilibrium conditions imposed by MS. Full article
(This article belongs to the Special Issue Materials Processing and Crystal Growth for Thermoelectrics)
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Open AccessArticle Helical Arrangement of 2-(4-hydroxy-3-methoxyphenyl)-Benzothiazole in Crystal Formation and Biological Evaluation on HeLa Cells
Crystals 2017, 7(6), 171; https://doi.org/10.3390/cryst7060171
Received: 3 May 2017 / Revised: 2 June 2017 / Accepted: 7 June 2017 / Published: 11 June 2017
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Abstract
Benzothiazoles are a set of molecules with a broad spectrum of biological applications. In particular, 2-(4-hydroxy-3-methoxyphenyl)-benzothiazole is a potential breast cancer cell suppressor whose mechanism of action has been previously reported. In the present work, the title compound was synthesized, crystallized, and its
[...] Read more.
Benzothiazoles are a set of molecules with a broad spectrum of biological applications. In particular, 2-(4-hydroxy-3-methoxyphenyl)-benzothiazole is a potential breast cancer cell suppressor whose mechanism of action has been previously reported. In the present work, the title compound was synthesized, crystallized, and its biological activity on HeLa cells was evaluated. Its molecular structure was compared to that obtained by molecular modeling. Theoretical calculations suggest that the syn-rotamer is the most stable form and correlates very well with crystallographic data. The crystal structure adopts a helical arrangement formed through O13—H13∙∙∙N3 intermolecular hydrogen bonding that propagates in the (14 -1 -3) plane. These results suggest that the title compound has the capacity to interleave into DNA and better explain its biological effects related to the increased CHIP expression through AhR recruitment. Finally, the biological experiments indicate that the title compound has the capacity to decrease the viability of HeLa cells with an IC50 = 2.86 μM. Full article
(This article belongs to the Section Interactions in Crystal Structures)
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Open AccessArticle Nb-Doped 0.8BaTiO3-0.2Bi(Mg0.5Ti0.5)O3 Ceramics with Stable Dielectric Properties at High Temperature
Crystals 2017, 7(6), 168; https://doi.org/10.3390/cryst7060168
Received: 6 April 2017 / Revised: 27 May 2017 / Accepted: 3 June 2017 / Published: 11 June 2017
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Abstract
Nb-doped 0.8BaTiO3-0.2Bi(Mg0.5Ti0.5)O3 ceramics were prepared by conventional solid-state method. The dielectric properties and the structural properties were investigated. When Nb2O5 is doped into 0.8BT-0.2BMT system, a small amount of Ba4Ti12
[...] Read more.
Nb-doped 0.8BaTiO3-0.2Bi(Mg0.5Ti0.5)O3 ceramics were prepared by conventional solid-state method. The dielectric properties and the structural properties were investigated. When Nb2O5 is doped into 0.8BT-0.2BMT system, a small amount of Ba4Ti12O27 secondary phase is formed. The lattice parameters gradually increase with the Nb2O5 doping. It is found that the temperature-capacitance characteristics greatly depend on Nb2O5 content. With the addition of 3.0 mol% Nb2O5, a 0.8BT-0.2BMT ceramic sample could satisfy the EIA X9R specification. This material is promising for high-temperature MLCC application. Full article
(This article belongs to the Special Issue Crystal Structure of Electroceramics) Printed Edition available
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Open AccessArticle Effect of an External Electric Field on the Kinetics of Dislocation-Free Growth of Tetragonal Hen Egg White Lysozyme Crystals
Crystals 2017, 7(6), 170; https://doi.org/10.3390/cryst7060170
Received: 28 April 2017 / Revised: 30 May 2017 / Accepted: 9 June 2017 / Published: 10 June 2017
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Abstract
Dislocation-free tetragonal hen egg white (HEW) lysozyme crystals were grown from a seed crystal in a cell. The rates of tetragonal HEW lysozyme crystal growth normal to the (110) and (101) faces with and without a 1-MHz external electric field were measured. A
[...] Read more.
Dislocation-free tetragonal hen egg white (HEW) lysozyme crystals were grown from a seed crystal in a cell. The rates of tetragonal HEW lysozyme crystal growth normal to the (110) and (101) faces with and without a 1-MHz external electric field were measured. A decrease in the typical growth rates of the crystal measured under an applied field at 1 MHz was observed, although the overall driving force increased. Assuming that the birth and spread mechanism of two-dimensional nucleation occurs, an increase in the effective surface energy of the step ends was realized in the presence of the electric field, which led to an improvement in the crystal quality of the tetragonal HEW lysozyme crystals. This article also discusses the increase in the effective surface energy of the step ends with respect to the change in the entropy of the solid. Full article
(This article belongs to the Special Issue Protein Crystallization under the Presence of an Electric Field)
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Open AccessArticle Investigation into the Effect of Sulfate and Borate Incorporation on the Structure and Properties of SrFeO3-δ
Crystals 2017, 7(6), 169; https://doi.org/10.3390/cryst7060169
Received: 28 April 2017 / Revised: 26 May 2017 / Accepted: 3 June 2017 / Published: 7 June 2017
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Abstract
In this paper, we demonstrate the successful incorporation of sulfate and borate into SrFeO3-δ, and characterise the effect on the structure and conductivity, with a view to possible utilisation as a cathode material in Solid Oxide Fuel Cells. The incorporation of
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In this paper, we demonstrate the successful incorporation of sulfate and borate into SrFeO3-δ, and characterise the effect on the structure and conductivity, with a view to possible utilisation as a cathode material in Solid Oxide Fuel Cells. The incorporation of low levels of sulfate/borate is sufficient to cause a change from a tetragonal to a cubic cell. Moreover, whereas heat treatment of undoped SrFeO3-δ under N2 leads to a transformation to brownmillerite Sr2Fe2O5 with oxygen vacancy ordering, the sulfate/borate-doped samples remain cubic under the same conditions. Thus, sulfate/borate doping appears to be successful in introducing oxide ion vacancy disorder in this system. Full article
(This article belongs to the Special Issue Crystal Structure of Electroceramics) Printed Edition available
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