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Crystals, Volume 7, Issue 4 (April 2017)

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Cover Story Yang et al. review the development of borate-based ultraviolet (UV) nonlinear optical (NLO) [...] Read more.
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Open AccessArticle Synthesis, Characterization and Catalytic Performance of Well-Ordered Crystalline Heteroatom Mesoporous MCM-41
Crystals 2017, 7(4), 89; doi:10.3390/cryst7040089
Received: 27 February 2017 / Revised: 16 March 2017 / Accepted: 17 March 2017 / Published: 23 March 2017
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Abstract
Mesoporous heteroatom molecular sieve MCM-41 bulk crystals with the crystalline phase were synthesized via a one-step hydrothermal method using an ionic complex as template. The ionic complex template was formed by interaction between cetyltrimethylammonium ions and metal complex ion [M(EDTA)]2− (M =
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Mesoporous heteroatom molecular sieve MCM-41 bulk crystals with the crystalline phase were synthesized via a one-step hydrothermal method using an ionic complex as template. The ionic complex template was formed by interaction between cetyltrimethylammonium ions and metal complex ion [M(EDTA)]2− (M = Co or Ni)]. The materials were characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, N2 adsorption-desorption isotherms, and X-ray absorption fine structure spectroscopy. The results showed that the materials possess a highly-ordered mesoporous structure with a crystalline phase and possess highly uniform ordered arrangement channels. The structure is in the vertical cross directions with a crystalline size of about 12 µm and high specific surface areas. The metal atoms were incorporated into the zeolite frameworks in the form of octahedral coordinate and have a uniform distribution in the materials. The amount of metal complexes formed by metal ion and EDTA is an essential factor for the formation of the vertical cross structure. Compared to Si-MCM-41, the samples exhibited better conversion and higher selectivity for cumene cracking. Full article
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Open AccessArticle Microstructure Evolution and Thermoelectric Property of Pt-PtRh Thin Film Thermocouples
Crystals 2017, 7(4), 96; doi:10.3390/cryst7040096
Received: 1 March 2017 / Revised: 23 March 2017 / Accepted: 24 March 2017 / Published: 25 March 2017
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Abstract
Due to their small size, extremely fast response, and low cost, refractory metallic thin film thermocouples (TFTCs) are well suited for the surface temperature measurement of hot components. In this study, PtRh films with different amounts of Rhodium (10% and 13%) were deposited
[...] Read more.
Due to their small size, extremely fast response, and low cost, refractory metallic thin film thermocouples (TFTCs) are well suited for the surface temperature measurement of hot components. In this study, PtRh films with different amounts of Rhodium (10% and 13%) were deposited with direct current magnetron sputtering and annealed at different temperatures in air. The chemistry, microstructure, and resistivity of the films were investigated. Type S (Pt10%Rh-Pt) and type R (Pt13%Rh-Pt) TFTC were fabricated on alumina substrates. Rhodium segregation at the surface of PtRh film was observed, and the variation of the thermoelectric properties of TFTCs was discussed based on the chemistry and microstructure of PtRh films. Full article
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Open AccessArticle Epitaxial Defects in Nanoscale InP Fin Structures Revealed by Wet-Chemical Etching
Crystals 2017, 7(4), 98; doi:10.3390/cryst7040098
Received: 18 January 2017 / Revised: 10 March 2017 / Accepted: 21 March 2017 / Published: 30 March 2017
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Abstract
In this work, we report on wet-chemical defect revealing in InP fin structures relevant for device manufacturing. Both HCl and HBr solutions were explored using bulk InP as a reference. A distinct difference in pit morphology was observed between the two acids, attributed
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In this work, we report on wet-chemical defect revealing in InP fin structures relevant for device manufacturing. Both HCl and HBr solutions were explored using bulk InP as a reference. A distinct difference in pit morphology was observed between the two acids, attributed to an anisotropy in step edge reactivity. The morphology of the etch pits in bulk InP suggests that the dislocations are oriented mainly perpendicular to the surface. By studying the influence of the acid concentration on the InP fin recess in nanoscale trenches, it was found that aqueous HCl solution was most suitable for revealing defects. Planar defects in InP fin structures grown by the aspect ratio trapping technique could be visualized as characteristic shallow grooves approximately one nanometer deep. It is challenging to reveal defects in wide-field InP fins. In these structures, dislocations also reach the surface next to stack faults or twinning planes. Due to the inclined nature, dislocation-related pits are only a few atomic layers deep. Extending the pits is limited by the high reactivity of the fin sides and the strong surface roughening during etching. The process window for revealing wet-chemical defects in InP fins is limited. Full article
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Open AccessArticle Enhanced Framework Rigidity of a Zeolitic Metal-Azolate via Ligand Substitution
Crystals 2017, 7(4), 99; doi:10.3390/cryst7040099
Received: 2 March 2017 / Revised: 25 March 2017 / Accepted: 27 March 2017 / Published: 31 March 2017
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Abstract
The elastic properties of a zeolitic metal-azolate framework, Zn(mtz)2 (MAF-7, mtz = 3-methyl-1,2,4-triazolate), have been examined from the view point of the first principles calculations and experiments. Our results demonstrate that the three independent elastic constants of MAF-7 are about 5.0–73.3%
[...] Read more.
The elastic properties of a zeolitic metal-azolate framework, Zn(mtz)2 (MAF-7, mtz = 3-methyl-1,2,4-triazolate), have been examined from the view point of the first principles calculations and experiments. Our results demonstrate that the three independent elastic constants of MAF-7 are about 5.0–73.3% higher than those of ZIF-8, though they are isomorphic. The electron-donating effect of the nitrogen atom at the 2-position in mtz- ring dominantly accounts for such a prominent difference. The detailed analysis of the full elastic tensors reveals that the volume moduli, shear moduli, and Poisson’s ratios of MAF-7 are about 3.4% to 20.1%, 3.2% to 20.6%, and −30.3% to 12.3% higher than those of ZIF-8. The underlying structural reasons were discussed to explain the anisotropic difference of those properties. Moreover, the conclusion deduced from first-principle calculations was also been verified by nanoindentation and high-pressure synchrotron X-ray diffraction measurements. Full article
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Open AccessArticle Morphology of Spherulites in Rapidly Solidified Ni3Ge Droplets
Crystals 2017, 7(4), 100; doi:10.3390/cryst7040100
Received: 26 January 2017 / Revised: 22 March 2017 / Accepted: 29 March 2017 / Published: 1 April 2017
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Abstract
The congruently melting, single phase, L12 intermetallic β-Ni3Ge has been subject to rapid solidification via drop-tube processing. Four different cooling rates are used in this process, at very low cooling rates (≥850 μm diameter particles, ≥700 K s−1)
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The congruently melting, single phase, L12 intermetallic β-Ni3Ge has been subject to rapid solidification via drop-tube processing. Four different cooling rates are used in this process, at very low cooling rates (≥850 μm diameter particles, ≥700 K s−1) and slightly higher cooling rates (850–500 μm diameter particles, 700–1386 K s−1) the dominant solidification morphology, revealed after etching, is that of isolated spherulites in an otherwise featureless matrix. At higher cooling rates, (500–300 μm diameter particles, 1386–2790 K s−1 and (300–212 μm diameter particles, 2790–4600 K s−1) mixed spherulite and dendritic morphologies are observed. Indeed, at the higher cooling rate dendrites with side-branches composed of numerous small spherulites are observed. Selected area diffraction analysis in the TEM indicate that the formation of spherulites is due to an order-disorder transformation. Dark-field TEM imaging has confirmed that the spherulites appear to consist of lamellae of the ordered phase, with disordered material in the space between the lamellae. The lamellar width within a given spherulite is constant, but the width is a function of cooling rate, with higher cooling rates giving finer lamellae. As such, there are many parallels with spherulite growth in polymers. Full article
(This article belongs to the Special Issue Crystal Morphology and Assembly in Spherulites)
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Open AccessArticle Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 Piezoelectric Single-Crystal Rectangular Beams: Mode-Coupling Effect and Its Application to Ultrasonic Array Transducers
Crystals 2017, 7(4), 101; doi:10.3390/cryst7040101
Received: 6 February 2017 / Revised: 17 March 2017 / Accepted: 23 March 2017 / Published: 2 April 2017
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Abstract
Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) piezoelectric single-crystal rectangular beams with the PIN:PMN:PT ratio of 0.33:0.35:0.32 are prepared, and their mode-coupling effect is investigated both theoretically and experimentally for ultrasonic array transducer applications. The
[...] Read more.
Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) piezoelectric single-crystal rectangular beams with the PIN:PMN:PT ratio of 0.33:0.35:0.32 are prepared, and their mode-coupling effect is investigated both theoretically and experimentally for ultrasonic array transducer applications. The PIN–PMN–PT rectangular beams become a tall-narrow beam and a short-wide plate, and so exhibiting an uncoupled height-extensional (beam) mode and an uncoupled thickness-extensional (plate) mode, at a width-to-height ratio G (= L / H) of <0.7 and >6.0, respectively. With G varying in the range of 1.6 to 3.1, the beam mode not only couples strongly with the width (lateral) mode, but also coexists obviously with the plate mode, giving high electromechanical coupling coefficients k_33^' and k_t of ~0.75 and ~0.50, respectively. With the guide of the mode-coupling results, a multifrequency ultrasonic array transducer having three distinct operational frequencies of 1.52, 2.60, and 6.01 MHz, corresponding to the coupled/coexistent beam mode, lateral mode, and plate mode, respectively, is developed using a mode-coupled rectangular beam of G = 1.6. Two different single-frequency ultrasonic array transducers, fabricated using two different uncoupled rectangular beams, one operating in uncoupled beam mode with G = 0.6 at 2.24 MHz and one working in uncoupled plate mode with G = 10.0 at 5.75 MHz, are also developed for comparison. Full article
(This article belongs to the Special Issue Crystal Growth for Optoelectronic and Piezoelectric Applications)
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Open AccessArticle Crystallographic Characteristics of Hydroxylapatite in Hard Tissues of Cololabis saira
Crystals 2017, 7(4), 103; doi:10.3390/cryst7040103
Received: 9 January 2017 / Revised: 20 March 2017 / Accepted: 1 April 2017 / Published: 5 April 2017
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Abstract
X-ray micro diffractometry, transmission electron microscopy, environmental scanning electron microscopy, energy dispersive spectrometry and Fourier transform infrared were employed to investigate the crystallographic characteristics of the inorganic mineral existing in bones of Cololabis saira. The results show that the crystal phase
[...] Read more.
X-ray micro diffractometry, transmission electron microscopy, environmental scanning electron microscopy, energy dispersive spectrometry and Fourier transform infrared were employed to investigate the crystallographic characteristics of the inorganic mineral existing in bones of Cololabis saira. The results show that the crystal phase in hard tissues of Cololabis saira is hydroxylapatite (HAP). Chemical composition analysis reveals that the HAP in hard tissues lacks P and is rich in Ca. Refined lattice parameters of HAP show that a = 0.93622–0.93787 nm and c = 0.68549–0.69011 nm. The domain sizes calculated from the Scherrer equation are 18.9–20.7 nm long along the c-axis and about 6.2 nm thick perpendicular to the c-axis, and is well evidenced by TEM data. The crystallinity of HAP is poor compared with natural HAP. In situ X-ray micro diffraction patterns measured from raw hard tissue show a very strong reflection from the (002) and (004) lattice planes on the cross-section of bone and nearly no reflection from the (002) and (004) lattice planes on elongation surface of bone. Compared with the XRD pattern of standard HAP data and from the textural index R values, it indicates that the HAP in the hard tissues of Cololabis saira has a strong preferring orientation along the crystallographic c-axis. This is verified by Fourier transform infrared on the elongation surface of bone and by selected area electron diffraction of HRTEM on the section perpendicular to elongation of bone. A quantitative textural degree index DR is proposed. The crystallographic characteristics of bio-hydroxylapatites (particle size, crystallinity and preferring orientation) are designed by tissue function and controlled by organic matrix to provide a good mechanical performance. Full article
(This article belongs to the Special Issue Mineral Crystallinity)
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Open AccessArticle Structure and Optical Properties of K0.67Rb1.33Al2B2O7 Crystal
Crystals 2017, 7(4), 104; doi:10.3390/cryst7040104
Received: 20 January 2017 / Revised: 23 March 2017 / Accepted: 4 April 2017 / Published: 7 April 2017
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Abstract
A UV nonlinear optical (NLO) crystal K0.67Rb1.33Al2B2O7 (KRABO) has been obtained by the top-seeded solution growth method for the first time. Its structure is formed of coplanar [BO3]3− triangle groups and
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A UV nonlinear optical (NLO) crystal K0.67Rb1.33Al2B2O7 (KRABO) has been obtained by the top-seeded solution growth method for the first time. Its structure is formed of coplanar [BO3]3− triangle groups and [Al2O7]8− groups, which are built from two [AlO4]5− tetrahedra sharing one vertex. Rb and K atoms have the same coordinates and locate between each layer in a disorderly fashion. The crystal has a larger NLO effect compared with its analog K2Al2B2O7 (KABO), as evidenced by powder second harmonic generation (SHG) test. The shortest SHG phase-matching wavelength is down to 231 nm according to the first-principle calculation, which indicates that KRABO is possible for the fourth harmonic generation of Nd:YAG at 266 nm. Full article
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Open AccessArticle Epoxy-Based Composites Embedded with High Performance BZT-0.5BCT Piezoelectric Nanoparticles Powders for Damping Vibration Absorber Application
Crystals 2017, 7(4), 105; doi:10.3390/cryst7040105
Received: 24 February 2017 / Revised: 6 April 2017 / Accepted: 6 April 2017 / Published: 9 April 2017
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Abstract
Abstract: Lead-free, high piezoelectric performance, Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-0.5BCT) sub-micron powders with perovskite structure were fabricated using the sol-gel process. A 0-3 type composite was obtained by choosing epoxy resin as matrix and BZT-0.5BCT,
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Abstract: Lead-free, high piezoelectric performance, Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 (BZT-0.5BCT) sub-micron powders with perovskite structure were fabricated using the sol-gel process. A 0-3 type composite was obtained by choosing epoxy resin as matrix and BZT-0.5BCT, acetylene black as functional phases. Particular attention was paid to the damping behavior of composite with different content of BZT-0.5BCT powders, the influence of frequency and loading force on the damping properties were also analyzed. A mathematical model was developed to characterize the damping properties of the composites. It found that the piezoelectric effects and interfacial friction play a key role in damping behavior of composites, and a large dissipated loss factor of tanδ was found at the BZT-0.5BCT content of 20 vol %. Full article
(This article belongs to the Special Issue Crystal Structure of Electroceramics)
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Open AccessArticle Quantum Phenomena Emerging Near a Ferroelectric Critical Point in a Donor–Acceptor Organic Charge-Transfer Complex
Crystals 2017, 7(4), 106; doi:10.3390/cryst7040106
Received: 13 March 2017 / Revised: 1 April 2017 / Accepted: 1 April 2017 / Published: 10 April 2017
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Abstract
When a second-order transition point is decreased to zero temperature, a continuous quantum phase transition between different ground states is realized at a quantum critical point (QCP). A recently synthesized organic charge-transfer complex, TTF-2,5-QBr2I2, provides a platform for the
[...] Read more.
When a second-order transition point is decreased to zero temperature, a continuous quantum phase transition between different ground states is realized at a quantum critical point (QCP). A recently synthesized organic charge-transfer complex, TTF-2,5-QBr 2 I 2 , provides a platform for the exploration of the quantum phenomena that accompany a ferroelectric QCP. Here, we summarize the recent results showing the quantum phenomena associated with the ferroelectric QCP in TTF-2,5-QBr 2 I 2 . Whereas the enhanced quantum fluctuations lead to quantitative changes in the critical exponents of the critical phenomena, they qualitatively change the nature of the domain-wall kinetics from thermally activated motion to temperature-independent tunneling motion. The present findings highlight the great influence of quantum fluctuations on the low-temperature physical properties and suggest that TTF-2,5-QBr 2 I 2 is a model system for the uniaxial ferroelectric QCP. Full article
(This article belongs to the Special Issue The Neutral–Ionic Phase Transition)
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Open AccessArticle Li2HgMS4 (M = Si, Ge, Sn): New Quaternary Diamond-Like Semiconductors for Infrared Laser Frequency Conversion
Crystals 2017, 7(4), 107; doi:10.3390/cryst7040107
Received: 23 February 2017 / Revised: 29 March 2017 / Accepted: 6 April 2017 / Published: 12 April 2017
Cited by 1 | PDF Full-text (3945 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A new family of quaternary diamond-like semiconductors (DLSs), Li2HgMS4 (M = Si, Ge, Sn), were successfully discovered for the first time. All of them are isostructural and crystallize in the polar space group (Pmn21). Seen from
[...] Read more.
A new family of quaternary diamond-like semiconductors (DLSs), Li2HgMS4 (M = Si, Ge, Sn), were successfully discovered for the first time. All of them are isostructural and crystallize in the polar space group (Pmn21). Seen from their structures, they exhibit a three-dimensional (3D) framework structure that is composed of countless 2D honeycomb layers stacked along the c axis. An interesting feature, specifically, that the LiS4 tetrahedra connect with each other to build a 2D layer in the ac plane, is also observed. Experimental investigations show that their nonlinear optical responses are about 0.8 for Li2HgSiS4, 3.0 for Li2HgGeS4, and 4.0 for Li2HgSnS4 times that of benchmark AgGaS2 at the 55–88 μm particle size, respectively. In addition, Li2HgSiS4 and Li2HgGeS4 also have great laser-damage thresholds that are about 3.0 and 2.3 times that of powdered AgGaS2, respectively. The above results indicate that title compounds can be expected as promising IR NLO candidates. Full article
(This article belongs to the Special Issue Crystal Structure of Electroceramics)
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Open AccessArticle Phenomenology of the Neutral-Ionic Valence Instability in Mixed Stack Charge-Transfer Crystals
Crystals 2017, 7(4), 108; doi:10.3390/cryst7040108
Received: 15 March 2017 / Revised: 4 April 2017 / Accepted: 6 April 2017 / Published: 11 April 2017
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Abstract
Organic charge-transfer (CT) crystals constitute an important class of functional materials, characterized by the directional charge-transfer interaction between π-electron Donor (D) and Acceptor (A) molecules, with the formation of one-dimensional ...DADAD... stacks. Among the many different and often unique phenomena displayed by
[...] Read more.
Organic charge-transfer (CT) crystals constitute an important class of functional materials, characterized by the directional charge-transfer interaction between π -electron Donor (D) and Acceptor (A) molecules, with the formation of one-dimensional ...DADAD... stacks. Among the many different and often unique phenomena displayed by this class of crystals, Neutral-Ionic phase transition (NIT) occupies a special place, as it implies a collective electron transfer along the stack. The analysis of such a complex yet fascinating phenomenon has required many years of investigation, and still presents some open questions and challenges. We present an updated and extensive summary of the phenomenology of the temperature induced NIT, with emphasis on the spectroscopic signatures of the transition. A much shorter summary is given for the NIT induced by pressure. Finally, we report on the exploration, by chemical substitution, of the phase space of ...DADAD... CT crystals, aimed at finding materials with important semiconducting or ferroelectric properties, and at understanding the subtle factors determining the crystal packing. Full article
(This article belongs to the Special Issue The Neutral–Ionic Phase Transition)
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Open AccessArticle Comparative Interrelationship of the Structural, Nonlinear-Optical and Other Acentric Properties for Oxide, Borate and Carbonate Crystals
Crystals 2017, 7(4), 109; doi:10.3390/cryst7040109
Received: 3 February 2017 / Revised: 22 March 2017 / Accepted: 28 March 2017 / Published: 12 April 2017
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Abstract
The structure and the maximal nonlinear optical (NLO) susceptibility χ(2) are tabulated for more 700 acentric binary oxides, 220 crystals of simple, binary and complex borates and for the same set of 110 carbonates, tartrates, formates, oxalates, acetates and fluoride-carbonates used in
[...] Read more.
The structure and the maximal nonlinear optical (NLO) susceptibility χ(2) are tabulated for more 700 acentric binary oxides, 220 crystals of simple, binary and complex borates and for the same set of 110 carbonates, tartrates, formates, oxalates, acetates and fluoride-carbonates used in ultraviolet and deep ultraviolet optoelectronics. According to the chemical formula, the structural symbols of these crystals have been plotted on the plane of two minimal oxide bond lengths (OBL). It is shown that acentric crystals are positioned on such plane inside the vertical, horizontal and slope intersected ellipses of “acentricity”. The oxide and borate crystals with moderate NLO susceptibility are found in the central parts of these ellipses intersection and, with low susceptibility, on top, at the bottom and border of the ellipses rosette. The nonpolar fluoride-carbonate crystals with high NLO susceptibility are found in the curve-side rhombic parts of the slope ellipse of “acentricity”. The unmonotonous fuzzy dependence “χ(2)” on the OBL of these crystals is observed, and their clear-cut taxonomy on compounds with π– or σ–oxide bonds is also established. It is shown that the correlations of χ(2) with other acentric properties are nonlinear for the whole set of the oxide crystals having their clear maximum at a certain value of the piezoelectric or electro-optic coefficient. The correlation “hardness–thermoconductivity-fusibility” is plotted for oxide crystals, part of which is used at the creation of self-frequency-doubling solid state lasers. Full article
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Open AccessArticle First-Principles Investigations on Structural and Elastic Properties of Orthorhombic TiAl under Pressure
Crystals 2017, 7(4), 111; doi:10.3390/cryst7040111
Received: 1 March 2017 / Revised: 3 April 2017 / Accepted: 5 April 2017 / Published: 13 April 2017
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Abstract
The effects of pressure on the structural and elastic properties of orthorhombic TiAl are investigated using first-principles calculations based on density functional theory within the projector augmented wave method. The calculated lattice parameters at 0 GPa are in good agreement with the available
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The effects of pressure on the structural and elastic properties of orthorhombic TiAl are investigated using first-principles calculations based on density functional theory within the projector augmented wave method. The calculated lattice parameters at 0 GPa are in good agreement with the available experimental data. The pressure dependence of the normalized lattice parameters and the single crystal elastic constants are investigated. By the elastic stability criteria under pressure, it is found that orthorhombic TiAl is mechanically stable under pressure up to 100 GPa. The elastic moduli and Poisson’s ratio under pressure up to 100 GPa are calculated using the Hill average method. The ductility/brittleness under pressure are evaluated, and a critical pressure for brittle-to-ductile transition is found to be 40 GPa. The elastic anisotropy and Debye temperature under different pressure are estimated from the calculations. Full article
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Open AccessArticle Synthesis, Crystal Structure, Photoluminescence Properties and Antibacterial Activity of a Zn(II) Coordination Polymer Based on a Paddle-Wheel Cluster
Crystals 2017, 7(4), 112; doi:10.3390/cryst7040112
Received: 15 March 2017 / Revised: 13 April 2017 / Accepted: 13 April 2017 / Published: 17 April 2017
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Abstract
A binuclear Zn(II) complex of formula {[Zn(BCPPO)H2O]•3C2H5OH}n (1) [H2BCPPO = Bis 4-carboxyphenyl phenyl phosphine oxide] has been synthesized and structurally characterized by single crystal X-ray diffraction, Powder X-ray diffraction (PXRD), Thermogravimetric analysis (TG), Elemental analysis (EA) and Infrared spectroscopy (IR). As revealed by
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A binuclear Zn(II) complex of formula {[Zn(BCPPO)H2O]•3C2H5OH}n (1) [H2BCPPO = Bis 4-carboxyphenyl phenyl phosphine oxide] has been synthesized and structurally characterized by single crystal X-ray diffraction, Powder X-ray diffraction (PXRD), Thermogravimetric analysis (TG), Elemental analysis (EA) and Infrared spectroscopy (IR). As revealed by the single crystal X-ray diffraction, in the binuclear Zn(II) complex, two paddle-wheel-type Zn2 units were connected by four BCPPO ligands to form one-dimensional chains. Their antibacterial activity was evaluated by using a minimal bactericidal concentration (MBC) benchmark. The binuclear Zn(II) complex shows excellent and long-term antibacterial activity against Escherichia coli and Staphylococcus aureus. In addition, the Photoluminescence properties of the binuclear Zn(II) complex was also investigated. Full article
(This article belongs to the Section Crystal Engineering)
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Open AccessArticle Chiral Optical Tamm States: Temporal Coupled-Mode Theory
Crystals 2017, 7(4), 113; doi:10.3390/cryst7040113
Received: 28 February 2017 / Revised: 4 April 2017 / Accepted: 8 April 2017 / Published: 17 April 2017
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Abstract
The chiral optical Tamm state (COTS) is a special localized state at the interface of a handedness-preserving mirror and a structurally chiral medium such as a cholesteric liquid crystal or a chiral sculptured thin film. The spectral behavior of COTS, observed as reflection
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The chiral optical Tamm state (COTS) is a special localized state at the interface of a handedness-preserving mirror and a structurally chiral medium such as a cholesteric liquid crystal or a chiral sculptured thin film. The spectral behavior of COTS, observed as reflection resonances, is described by the temporal coupled-mode theory. Mode coupling is different for two circular light polarizations because COTS has a helical structure replicating that of the cholesteric. The mode coupling for co-handed circularly polarized light exponentially attenuates with the cholesteric layer thickness since the COTS frequency falls into the stop band. Cross-handed circularly polarized light freely goes through the cholesteric layer and can excite COTS when reflected from the handedness-preserving mirror. The coupling in this case is proportional to anisotropy of the cholesteric and theoretically only anisotropy in magnetic permittivity can ultimately cancel this coupling. These two couplings being equal result in a polarization crossover (the Kopp–Genack effect) for which a linear polarization is optimal to excite COTS. The corresponding cholesteric thickness and scattering matrix for COTS are generally described by simple expressions. Full article
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Open AccessArticle Fabrication of Low Dislocation Density, Single-Crystalline Diamond via Two-Step Epitaxial Lateral Overgrowth
Crystals 2017, 7(4), 114; doi:10.3390/cryst7040114
Received: 15 March 2017 / Revised: 13 April 2017 / Accepted: 17 April 2017 / Published: 18 April 2017
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Abstract
Continuous diamond films with low dislocation density were obtained by two-step epitaxial lateral overgrowth (ELO). Grooves were fabricated by inductively coupled plasma etching. Mo/Pd stripes sputtered in the grooves were used to inhibit the propagation of dislocations originating from the diamond substrate. Coalescent
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Continuous diamond films with low dislocation density were obtained by two-step epitaxial lateral overgrowth (ELO). Grooves were fabricated by inductively coupled plasma etching. Mo/Pd stripes sputtered in the grooves were used to inhibit the propagation of dislocations originating from the diamond substrate. Coalescent diamond films were achieved by ELO via microwave plasma-enhanced chemical vapor deposition. Etch-pits were formed intentionally to characterize the quality of the epitaxial films and distinguish different growth areas, as dislocations served as preferential sites for etching. In the window regions, a high density of dislocations, displayed as dense etch-pits, was generated. By contrast, the etch-pit density was clearly lower in the overgrowth regions. After the second ELO step, the dislocation density was further decreased. Raman spectroscopy analysis suggested that the lateral overgrowth of diamond is a promising method for achieving low dislocation density films. Full article
(This article belongs to the Special Issue Diamond Crystals)
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Open AccessArticle Thermochemical Wear of Single Crystal Diamond Catalyzed by Ferrous Materials at Elevated Temperature
Crystals 2017, 7(4), 116; doi:10.3390/cryst7040116
Received: 25 March 2017 / Revised: 15 April 2017 / Accepted: 17 April 2017 / Published: 19 April 2017
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Abstract
Single crystal diamond has been recognized as the optimal tool material in ultra-precision machining. However, the excessive tool wear prevents it from cutting ferrous materials. This paper conducts a series of thermal analysis tests under the conditions of different gas atmospheres, heating temperatures,
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Single crystal diamond has been recognized as the optimal tool material in ultra-precision machining. However, the excessive tool wear prevents it from cutting ferrous materials. This paper conducts a series of thermal analysis tests under the conditions of different gas atmospheres, heating temperatures, crystallographic planes and workpiece materials, in order to clarify the details of thermochemical wear of diamond catalyzed by iron at elevated temperature. Raman scattering analysis was performed to identify the transformation of diamond crystal structure. Energy dispersive X-ray analysis was used to detect the change in chemical composition of the work material. X-ray photoelectron spectroscopy was adopted to confirm the resultants of interfacial thermochemical reactions. The experimental results revealed that the diamond wear included the graphitization, diffusion and oxidation. Temperature was considered as the key factor affecting these wear mechanisms. The initial graphitization temperatures of diamond catalyzed by iron under different conditions were obtained, and the graphitized degree relied heavily on the crystallographic plane while being insensitive to the workpiece material. The diffusion wear rule was preliminarily achieved by the established prediction model of the carbon atoms diffusing into the iron lattice, and the types and resultants of interfacial chemical reactions were deduced. Full article
(This article belongs to the Special Issue Diamond Crystals)
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Open AccessArticle Study on Micro Morphology of Potassium Dihydrogen Phosphate Crystals Grown at Elevated Temperatures
Crystals 2017, 7(4), 118; doi:10.3390/cryst7040118
Received: 7 March 2017 / Revised: 7 April 2017 / Accepted: 18 April 2017 / Published: 21 April 2017
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Abstract
Potassium dihydrogen phosphate crystals were grown around 65 °C. The growth rate of KDP (KH2PO4) crystal prismatic faces was measured by laser polarization interference system. The surface micro morphology of KDP crystals grown at various supersaturation were comparatively observed
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Potassium dihydrogen phosphate crystals were grown around 65 °C. The growth rate of KDP (KH2PO4) crystal prismatic faces was measured by laser polarization interference system. The surface micro morphology of KDP crystals grown at various supersaturation were comparatively observed by atomic force microscope systematically. The results show that the growth rate increased with the rise of supersaturation, the aspect ratio reduced. The steps bunching height occurred at σ = 0.03 and 0.04. At this point, the steps height reached maximum value about 11.3~24.4 nm. The step bunching was almost constant at higher supersaturation. A few pits and holes appeared on the crystal surface at high supersaturation. In our opinion, the forming of these pits and holes might be related with the step movement and 2D nuclei mechanism. Full article
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Review

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Open AccessReview Borate-Based Ultraviolet and Deep-Ultraviolet Nonlinear Optical Crystals
Crystals 2017, 7(4), 95; doi:10.3390/cryst7040095
Received: 28 January 2017 / Revised: 9 March 2017 / Accepted: 21 March 2017 / Published: 25 March 2017
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Abstract
Borates have long been recognized as a very important family of nonlinear optical (NLO) crystals, and have been widely used in the laser frequency-converting technology in ultraviolet (UV) and deep-ultraviolet (DUV) regions. In this work, the borate-based UV and DUV NLO crystals discovered
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Borates have long been recognized as a very important family of nonlinear optical (NLO) crystals, and have been widely used in the laser frequency-converting technology in ultraviolet (UV) and deep-ultraviolet (DUV) regions. In this work, the borate-based UV and DUV NLO crystals discovered in the recent decade are reviewed, and the structure–property relationship in the representative borate-based UV and DUV NLO crystals is analyzed. It is concluded that the optical properties of these crystals can be well explained directly from the types and spatial arrangements of B-O groups. The deduced mechanism understanding has significant implications for the exploration and design of new borate-based crystals with excellent UV and DUV NLO performance. Full article
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Open AccessReview Ice Microstructure and Fabric of Guliya Ice Cap in Tibetan Plateau, and Comparisons with Vostok3G-1, EPICA DML, and North GRIP
Crystals 2017, 7(4), 97; doi:10.3390/cryst7040097
Received: 17 January 2017 / Revised: 20 March 2017 / Accepted: 22 March 2017 / Published: 30 March 2017
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Abstract
This work is the first in the general natural ice literature to compare microstructures and fabrics of continent-type mountain ice in mid-low latitudes with polar ice in order to find out how they evolved based on similar fabric patterns of their vertically girdles.
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This work is the first in the general natural ice literature to compare microstructures and fabrics of continent-type mountain ice in mid-low latitudes with polar ice in order to find out how they evolved based on similar fabric patterns of their vertically girdles. Microstructures and fabrics along the Guliya ice core on the Tibetan Plateau, China, were measured at a depth interval of approximately 10 m. The grain sizes increase unevenly with depth. The fabric patterns vary from the isotropic fabric, to broad single maximum, to vertical girdle, to single-maximum, and finally to multiple-maximum fabric. The grain growth rate of the Guliya core is faster than that of the Vostok3G-1, the EPICA DML, and the North GRIP. The vertical girdle fabric of the Guliya core forms at a high temperature and low strain rate. The strong single maximum fabric of the Guliya core appears in the mid-low part of the core with vertical uniaxial compression or simple shear. The thermal kinemics caused by the temperature can play a vital role in different stress cases to cast the similar or same fabric patterns. Normal grain growth, polygonization/rotation recrystallization, and migration recrystallization play roles different importance at different depths. Full article
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Open AccessReview Computer Simulations of Crystal Growth Using a Hard-Sphere Model
Crystals 2017, 7(4), 102; doi:10.3390/cryst7040102
Received: 19 December 2016 / Revised: 26 March 2017 / Accepted: 29 March 2017 / Published: 4 April 2017
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Abstract
A review of computer simulation studies on crystal growth in hard-sphere systems is presented. A historical view on the crystallization of hard spheres, including colloidal crystallization, is given in the first section. Crystal phase transition in a system comprising particles without bonding is
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A review of computer simulation studies on crystal growth in hard-sphere systems is presented. A historical view on the crystallization of hard spheres, including colloidal crystallization, is given in the first section. Crystal phase transition in a system comprising particles without bonding is difficult to understand. In the early days, therefore, many researchers did not accept such crystalline structures as crystals that should be studied in the field of crystal growth. In the last few decades, however, colloidal crystallization has drawn attention because in situ observations of crystallization process has become possible. Next, simulation studies of the crystal/fluid interface of hard spheres are also reviewed. Although colloidal crystallization has now been recognized in the crystal growth field, the stability of the crystal–fluid coexistence state has still not been satisfactorily understood based on a bond-breaking picture, because of an infinite diffuseness of the interfaces in non-bonding systems derived from this picture. Studies of sedimentary colloidal crystallization and colloidal epitaxy using the hard-sphere model are lastly reviewed. An advantage of the colloidal epitaxy is also presented; it is shown that a template not only fixes the crystal growth direction, but also improves the colloidal crystallization. A new technique for reducing defects in colloidal crystals through the gravity effect is also proposed. Full article
(This article belongs to the Special Issue Advances in Computer Simulation Studies on Crystal Growth)
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Open AccessFeature PaperReview Functionalisation of Colloidal Transition Metal Sulphides Nanocrystals: A Fascinating and Challenging Playground for the Chemist
Crystals 2017, 7(4), 110; doi:10.3390/cryst7040110
Received: 27 December 2016 / Revised: 22 March 2017 / Accepted: 24 March 2017 / Published: 14 April 2017
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Abstract
Metal sulphides, and in particular transition metal sulphide colloids, are a broad, versatile and exciting class of inorganic compounds which deserve growing interest and attention ascribable to the functional properties that many of them display. With respect to their oxide homologues, however, they
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Metal sulphides, and in particular transition metal sulphide colloids, are a broad, versatile and exciting class of inorganic compounds which deserve growing interest and attention ascribable to the functional properties that many of them display. With respect to their oxide homologues, however, they are characterised by noticeably different chemical, structural and hence functional features. Their potential applications span several fields, and in many of the foreseen applications (e.g., in bioimaging and related fields), the achievement of stable colloidal suspensions of metal sulphides is highly desirable or either an unavoidable requirement to be met. To this aim, robust functionalisation strategies should be devised, which however are, with respect to metal or metal oxides colloids, much more challenging. This has to be ascribed, inter alia, also to the still limited knowledge of the sulphides surface chemistry, particularly when comparing it to the better established, though multifaceted, oxide surface chemistry. A ground-breaking endeavour in this field is hence the detailed understanding of the nature of the complex surface chemistry of transition metal sulphides, which ideally requires an integrated experimental and modelling approach. In this review, an overview of the state-of-the-art on the existing examples of functionalisation of transition metal sulphides is provided, also by focusing on selected case studies, exemplifying the manifold nature of this class of binary inorganic compounds. Full article
(This article belongs to the Special Issue Colloidal Nanocrystals: Synthesis, Characterization and Application)
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Open AccessReview Morphological Control of Polymer Spherulites via Manipulating Radial Lamellar Organization upon Evaporative Crystallization: A Mini Review
Crystals 2017, 7(4), 115; doi:10.3390/cryst7040115
Received: 21 March 2017 / Revised: 17 April 2017 / Accepted: 17 April 2017 / Published: 19 April 2017
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Abstract
Various spherulites or spherulitic crystals are widely encountered in polymeric materials when crystallized from viscous melts or concentrated solutions. However, the microstructures and growth processes are quite complicated and remain unclear and, thus, the formation mechanisms are rather elusive. Here, diverse kinds of
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Various spherulites or spherulitic crystals are widely encountered in polymeric materials when crystallized from viscous melts or concentrated solutions. However, the microstructures and growth processes are quite complicated and remain unclear and, thus, the formation mechanisms are rather elusive. Here, diverse kinds of spherulitic growths and patterns of typical polyesters via evaporative crystallization of solution-cast thin films are delineated after detailed investigating the microstructures and in situ following the developing processes. The spherulitic crystals produced under different evaporation conditions reflect variously optical features, such as the usual Maltese Cross, non-birefringent or half-birefringent concentric-rings, extinction spiral banding, and even a nested ring-banded pattern. Polymer spherulites are composed of stacks of radial fibrillar lamellae, and the diversity of bewitchingly spherulitic morphologies is dominated by the arrangement and organization of radial lamellae, which is predicted to be tunable by modulating the evaporative crystallization processes. The emergence of various types of spherulitic morphologies of the same polymer is attributed to a precise manipulation of the radial lamellar organization by a coupling of structural features and specific crystal evolving courses under confined evaporation environments. The present findings improve dramatically the understanding of the structural development and crystallization mechanism for emergence of diverse polymer spherulitic morphologies. Full article
(This article belongs to the Special Issue Crystal Morphology and Assembly in Spherulites)
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Open AccessReview The Synergetic Effects of Combining Structural Biology and EPR Spectroscopy on Membrane Proteins
Crystals 2017, 7(4), 117; doi:10.3390/cryst7040117
Received: 14 February 2017 / Revised: 9 April 2017 / Accepted: 12 April 2017 / Published: 20 April 2017
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Abstract
Protein structures as provided by structural biology such as X-ray crystallography, cryo-electron microscopy and NMR spectroscopy are key elements to understand the function of a protein on the molecular level. Nonetheless, they might be error-prone due to crystallization artifacts or, in particular in
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Protein structures as provided by structural biology such as X-ray crystallography, cryo-electron microscopy and NMR spectroscopy are key elements to understand the function of a protein on the molecular level. Nonetheless, they might be error-prone due to crystallization artifacts or, in particular in case of membrane-imbedded proteins, a mostly artificial environment. In this review, we will introduce different EPR spectroscopy methods as powerful tools to complement and validate structural data gaining insights in the dynamics of proteins and protein complexes such that functional cycles can be derived. We will highlight the use of EPR spectroscopy on membrane-embedded proteins and protein complexes ranging from receptors to secondary active transporters as structural information is still limited in this field and the lipid environment is a particular challenge. Full article
(This article belongs to the Special Issue Recent Advances in Protein Crystallography)
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Other

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Open AccessLetter Formation of GaAs/GaSb Core-Shell Heterostructured Nanowires Grown by Molecular-Beam Epitaxy
Crystals 2017, 7(4), 94; doi:10.3390/cryst7040094
Received: 28 February 2017 / Revised: 21 March 2017 / Accepted: 22 March 2017 / Published: 24 March 2017
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Abstract
In this paper, we demonstrated the growth of GaAs/GaSb core-shell heterostructured nanowires on GaAs substrates, with the assistance of Au catalysts by molecular-beam epitaxy. Time-evolution experiments were designed to study the formation of GaSb shells with different growth times. It was found that,
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In this paper, we demonstrated the growth of GaAs/GaSb core-shell heterostructured nanowires on GaAs substrates, with the assistance of Au catalysts by molecular-beam epitaxy. Time-evolution experiments were designed to study the formation of GaSb shells with different growth times. It was found that, by comparing the morphology of nanowires for various growth times, lateral growth was taking a dominant position since GaSb growth began and bulgy GaSb particles formed on the nanowire tips during the growth. The movement of catalyst Au droplets was witnessed, thus, the radial growth was enhanced by sidewall nucleation under the vapor-solid mechanism due to the lack of driving force for axial growth. Moreover, compositional and structural characteristics of the GaAs/GaSb core-shell heterostructured nanowires were investigated by electron microscopy. Differing from the commonly anticipated result, GaSb shells took a wurzite structure instead of a zinc-blende structure to form the GaAs/GaSb wurzite/wurzite core-shell heterostructured nanowires, which is of interest to the research of band-gap engineering. This study provides a significant insight into the formation of core-shell heterostructured nanowires. Full article
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