Crystals

1106 KiB

Open AccessArticle

Sol–Gel-Derived Glass-Ceramic Photorefractive Films for Photonic Structures

by Anna Lukowiak, Lidia Zur, Thi Ngoc Lam Tran, Marcello Meneghetti, Simone Berneschi, Gualtiero Nunzi Conti, Stefano Pelli, Cosimo Trono, B.N. Shivakiran Bhaktha, Daniele Zonta, Stefano Taccheo, Giancarlo C. Righini and Maurizio Ferrari

Crystals 2017, 7(2), 61; https://doi.org/10.3390/cryst7020061 - 21 Feb 2017

Cited by 23 | Viewed by 5796

Abstract

Glass photonics are widespread, from everyday objects around us to high-tech specialized devices. Among different technologies, sol–gel synthesis allows for nanoscale materials engineering by exploiting its unique structures, such as transparent glass-ceramics, to tailor optical and electromagnetic properties and to boost photon-management yield. [...] Read more.

Glass photonics are widespread, from everyday objects around us to high-tech specialized devices. Among different technologies, sol–gel synthesis allows for nanoscale materials engineering by exploiting its unique structures, such as transparent glass-ceramics, to tailor optical and electromagnetic properties and to boost photon-management yield. Here, we briefly discuss the state of the technology and show that the choice of the sol–gel as a synthesis method brings the advantage of process versatility regarding materials composition and ease of implementation. In this context, we present tin-dioxide–silica (SnO₂–SiO₂) glass-ceramic waveguides activated by europium ions (Eu³⁺). The focus is on the photorefractive properties of this system because its photoluminescence properties have already been discussed in the papers presented in the bibliography. The main findings include the high photosensitivity of sol–gel 25SnO₂:75SiO₂ glass-ceramic waveguides; the ultraviolet (UV)-induced refractive index change (Δn ~ −1.6 × 10⁻³), the easy fabrication process, and the low propagation losses (0.5 ± 0.2 dB/cm), that make this glass-ceramic an interesting photonic material for smart optical applications. Full article

(This article belongs to the Special Issue Crystallization of Sol-Gel Derived Glasses)

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4478 KiB

Open AccessArticle

Synthesis, Crystal Structure, Spectroscopic Properties, and DFT Studies of 7,9-Dibromobenzo[h]quinolin-10-ol

by Hsing-Yang Tsai, Yuan Jay Chang, Jiun-Wei Hu and Kew-Yu Chen

Crystals 2017, 7(2), 60; https://doi.org/10.3390/cryst7020060 - 21 Feb 2017

Cited by 2 | Viewed by 4696

Abstract

7,9-Dibromobenzo[h]quinolin-10-ol (1), a benzo[h]quinolin-10-ol derivative, was synthesized and characterized by single-crystal X-ray diffraction. The crystal belongs to monoclinic space group P2₁/n, with a = 3.9573(4), b = 18.0416(18), c = 15.8210(16) Å, [...] Read more.

7,9-Dibromobenzo[h]quinolin-10-ol (1), a benzo[h]quinolin-10-ol derivative, was synthesized and characterized by single-crystal X-ray diffraction. The crystal belongs to monoclinic space group P2₁/n, with a = 3.9573(4), b = 18.0416(18), c = 15.8210(16) Å, α = 90°, β = 96.139(3)°, and γ = 90°. Compound 1 exhibits an intramolecular six-membered-ring hydrogen bond, from which excited-state intramolecular proton transfer takes place, resulting in a proton-transfer tautomer emission of 625 nm in cyclohexane. The crystal structure is stabilized by intermolecular π–π interactions, which links a pair of molecules into a cyclic centrosymmetric dimer. Furthermore, the geometric structures, frontier molecular orbitals, and potential energy curves (PECs) for 1 in the ground and the first singlet excited state were fully rationalized by density functional theory (DFT) and time-dependent DFT calculations. Full article

(This article belongs to the Special Issue Polar and Centrosymmetric Packings in Molecular Crystals)

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2842 KiB

Open AccessArticle

Optimization of Enzyme-Mediated Calcite Precipitation as a Soil-Improvement Technique: The Effect of Aragonite and Gypsum on the Mechanical Properties of Treated Sand

by Heriansyah Putra, Hideaki Yasuhara, Naoki Kinoshita and Akira Hirata

Crystals 2017, 7(2), 59; https://doi.org/10.3390/cryst7020059 - 20 Feb 2017

Cited by 54 | Viewed by 6654

Abstract

The effectiveness of magnesium as a substitute material in enzyme-mediated calcite precipitation was evaluated. Magnesium sulfate was added to the injecting solution composed of urea, urease, and calcium chloride. The effect of the substitution on the amount of precipitated materials was evaluated through [...] Read more.

The effectiveness of magnesium as a substitute material in enzyme-mediated calcite precipitation was evaluated. Magnesium sulfate was added to the injecting solution composed of urea, urease, and calcium chloride. The effect of the substitution on the amount of precipitated materials was evaluated through precipitation tests. X-ray powder diffraction and scanning electron microscopy analyses were conducted to examine the mineralogical morphology of the precipitated minerals and to determine the effect of magnesium on the composition of the precipitated materials. In addition to calcite, aragonite and gypsum were formed as the precipitated materials. The effect of the presence of aragonite and gypsum, in addition to calcite, as a soil-improvement technique was evaluated through unconfined compressive strength tests. Soil specimens were prepared in polyvinyl chloride cylinders and treated with concentration-controlled solutions, which produced calcite, aragonite, and gypsum. The mineralogical analysis revealed that the low and high concentrations of magnesium sulfate effectively promoted the formation of aragonite and gypsum, respectively. The injecting solutions which produced aragonite and calcite brought about a significant improvement in soil strength. The presence of the precipitated materials, comprising 10% of the soil mass within a treated sand, generated a strength of 0.6 MPa. Full article

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5912 KiB

Open AccessArticle

Molecular Dynamics Simulations of Hydroxyapatite Nanopores in Contact with Electrolyte Solutions: The Effect of Nanoconfinement and Solvated Ions on the Surface Reactivity and the Structural, Dynamical, and Vibrational Properties of Water

by Devis Di Tommaso, Muthuramalingam Prakash, Thibault Lemaire, Marius Lewerenz, Nora H. De Leeuw and Salah Naili

Crystals 2017, 7(2), 57; https://doi.org/10.3390/cryst7020057 - 18 Feb 2017

Cited by 21 | Viewed by 9420

Abstract

Hydroxyapatite, the main mineral phase of mammalian tooth enamel and bone, grows within nanoconfined environments and in contact with aqueous solutions that are rich in ions. Hydroxyapatite nanopores of different pore sizes (20 Å ≤ H ≤ 110 Å, where H is the [...] Read more.

Hydroxyapatite, the main mineral phase of mammalian tooth enamel and bone, grows within nanoconfined environments and in contact with aqueous solutions that are rich in ions. Hydroxyapatite nanopores of different pore sizes (20 Å ≤ H ≤ 110 Å, where H is the size of the nanopore) in contact with liquid water and aqueous electrolyte solutions (CaCl₂ (aq) and CaF₂ (aq)) were investigated using molecular dynamics simulations to quantify the effect of nanoconfinement and solvated ions on the surface reactivity and the structural and dynamical properties of water. The combined effect of solution composition and nanoconfinement significantly slows the self-diffusion coefficient of water molecules compared with bulk liquid. Analysis of the pair and angular distribution functions, distribution of hydrogen bonds, velocity autocorrelation functions, and power spectra of water shows that solution composition and nanoconfinement in particular enhance the rigidity of the water hydrogen bonding network. Calculation of the water exchange events in the coordination of calcium ions reveals that the dynamics of water molecules at the HAP–solution interface decreases substantially with the degree of confinement. Ions in solution also reduce the water dynamics at the surface calcium sites. Together, these changes in the properties of water impart an overall rigidifying effect on the solvent network and reduce the reactivity at the hydroxyapatite-solution interface. Since the process of surface-cation-dehydration governs the kinetics of the reactions occurring at mineral surfaces, such as adsorption and crystal growth, this work shows how nanoconfinement and solvation environment influence the molecular-level events surrounding the crystallization of hydroxyapatite. Full article

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

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2757 KiB

Open AccessArticle

Silver Nanoprism-Loaded Eggshell Membrane: A Facile Platform for In Situ SERS Monitoring of Catalytic Reactions

by Yaling Li, Yong Ye, Yunde Fan, Ji Zhou, Li Jia, Bin Tang and Xungai Wang

Crystals 2017, 7(2), 45; https://doi.org/10.3390/cryst7020045 - 18 Feb 2017

Cited by 17 | Viewed by 7223

Abstract

We reported the fabrication of an in situ surface-enhanced Raman scattering (SERS) monitoring platform, comprised of a porous eggshell membrane (ESM) bioscaffold loaded with Ag nanoprism via an electrostatic self-assembly approach. The localized surface plasmon resonance (LSPR) property of silver nanoprism leads to [...] Read more.

We reported the fabrication of an in situ surface-enhanced Raman scattering (SERS) monitoring platform, comprised of a porous eggshell membrane (ESM) bioscaffold loaded with Ag nanoprism via an electrostatic self-assembly approach. The localized surface plasmon resonance (LSPR) property of silver nanoprism leads to the blue color of the treated ESMs. UV-vis diffuse reflectance spectroscopy, scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements were employed to observe the microstructure and surface property of Ag nanoprisms on the ESMs. The silver nanoprism-loaded eggshell membrane (AgNP@ESM) exhibited strong catalytic activity for the reduction of 4-nitrophenol by sodium borohydride (NaBH₄) and it can be easily recovered and reused for more than six cycles. Significantly, the composites also display excellent SERS efficiency, allowing the in situ SERS monitoring of molecular transformation in heterogeneous catalysis. The results indicate that the AgNP@ESM biocomposite can achieve both SERS and catalytic functionalities simultaneously in a single entity with high performance, which promotes the potential applications of ESM modified with functional materials. Full article

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3813 KiB

Open AccessArticle

Anisotropic Magnetic Responses of Topological Crystalline Superconductors

by Yuansen Xiong, Ai Yamakage, Shingo Kobayashi, Masatoshi Sato and Yukio Tanaka

Crystals 2017, 7(2), 58; https://doi.org/10.3390/cryst7020058 - 17 Feb 2017

Cited by 22 | Viewed by 5228

Abstract

Majorana Kramers pairs emerged on surfaces of time-reversal-invariant topological crystalline superconductors show the Ising anisotropy to an applied magnetic ﬁeld. We clarify that crystalline symmetry uniquely determines the direction of the Majorana Ising spin for given irreduciblerepresentationsofpairpotential,derivingconstraintstotopologicalinvariants. In addition, necessary conditions for nontrivial [...] Read more.

Majorana Kramers pairs emerged on surfaces of time-reversal-invariant topological crystalline superconductors show the Ising anisotropy to an applied magnetic ﬁeld. We clarify that crystalline symmetry uniquely determines the direction of the Majorana Ising spin for given irreduciblerepresentationsofpairpotential,derivingconstraintstotopologicalinvariants. In addition, necessary conditions for nontrivial topological invariants protected by the n-fold rotational symmetry are shown. Full article

(This article belongs to the Special Issue Topological Crystalline Insulators: Current Progress and Prospects)

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3306 KiB

Open AccessArticle

Indium Substitution Effect on the Topological Crystalline Insulator Family (Pb_1−xSn_x)_1−yIn_yTe: Topological and Superconducting Properties

by Ruidan Zhong, John Schneeloch, Qiang Li, Wei Ku, John Tranquada and Genda Gu

Crystals 2017, 7(2), 55; https://doi.org/10.3390/cryst7020055 - 16 Feb 2017

Cited by 21 | Viewed by 8205

Abstract

Topological crystalline insulators (TCIs) have been of great interest in the area of condensed matter physics. We investigated the effect of indium substitution on the crystal structure and transport properties in the TCI system (Pb_1−xSn_x)_1−yIn [...] Read more.

Topological crystalline insulators (TCIs) have been of great interest in the area of condensed matter physics. We investigated the effect of indium substitution on the crystal structure and transport properties in the TCI system (Pb_1−xSn_x)_1−yIn_yTe. For samples with a tin concentration

x \leq 50 %

, the low-temperature resisitivities show a dramatic variation as a function of indium concentration: with up to ∼2% indium doping, the samples show weak-metallic behavior similar to their parent compounds; with ∼6% indium doping, samples have true bulk-insulating resistivity and present evidence for nontrivial topological surface states; with higher indium doping levels, superconductivity was observed, with a transition temperature,

T_{c}

, positively correlated to the indium concentration and reaching as high as 4.7 K. We address this issue from the view of bulk electronic structure modified by the indium-induced impurity level that pins the Fermi level. The current work summarizes the indium substitution effect on (Pb,Sn)Te, and discusses the topological and superconducting aspects, which can be provide guidance for future studies on this and related systems. Full article

(This article belongs to the Special Issue Topological Crystalline Insulators: Current Progress and Prospects)

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10192 KiB

Open AccessArticle

Interior Lamellar Assembly and Optical Birefringence in Poly(trimethylene terephthalate) Spherulites: Mechanisms from Past to Present

by Graecia Lugito, Eamor M. Woo and Wei-Tsung Chuang

Crystals 2017, 7(2), 56; https://doi.org/10.3390/cryst7020056 - 15 Feb 2017

Cited by 28 | Viewed by 7830

Abstract

Poly(trimethylene terephthalate) (PTT) with its unique spherulitic morphologies, highly birefringent features, and crystal stability serves as a good candidate to study polymer crystallization and assembly. This review compiles the main findings on crystallization in PTT, including birefringence and morphology, thermal behavior, as well [...] Read more.

Poly(trimethylene terephthalate) (PTT) with its unique spherulitic morphologies, highly birefringent features, and crystal stability serves as a good candidate to study polymer crystallization and assembly. This review compiles the main findings on crystallization in PTT, including birefringence and morphology, thermal behavior, as well as the interior structure of PTT banded spherulites, in order to elucidate the origin and formation mechanism of banded spherulites. Interior observation through the inner anatomy of crystal assembly in banded spherulites hidden under the top surface is necessary to provide a complete picture for the unsettled arguments about formation mechanism. Careful attention should be taken when selecting the etching agent for exposing the lamellar structure of polymer spherulite, otherwise, misinterpretation could result Full article

(This article belongs to the Special Issue Crystal Morphology and Assembly in Spherulites)

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937 KiB

Open AccessArticle

Ab Initio Study of the Elastic and Mechanical Properties of B19 TiAl

by Yufeng Wen, Long Wang, Huilong Liu and Lin Song

Crystals 2017, 7(2), 39; https://doi.org/10.3390/cryst7020039 - 15 Feb 2017

Cited by 41 | Viewed by 5739

Abstract

A theoretical study of the structural, elastic, and mechanical properties of B19 TiAl intermetallic compound with orthorhombic structure has been carried out by using ab initio density functional theory calculations based on the projector augmented wave and the generalized gradient approximation. The optimized [...] Read more.

A theoretical study of the structural, elastic, and mechanical properties of B19 TiAl intermetallic compound with orthorhombic structure has been carried out by using ab initio density functional theory calculations based on the projector augmented wave and the generalized gradient approximation. The optimized structure parameters are found to be in agreement with the available experimental data. The orthorhombic B19 structure of TiAl is found to be mechanically stable at ground state in terms of formation energy and single crystal elastic constants. Additionally, the polycrystalline bulk, shear and Young’s moduli, Poisson’s ratio, Cauchy pressure, and anisotropy factors are obtained from the single crystal elastic constants. At ground state, the B19 TiAl is found to not only have intrinsic brittleness in terms of Pugh’s ratio, Poisson’s ratio, and Cauchy pressure, but also exhibit elastic anisotropy in terms of elastic anisotropy factors and orientation dependence of Young’s modulus. Full article

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2936 KiB

Open AccessArticle

A Scheme for the Growth of Graphene Sheets Embedded with Nanocones

by Yu-Peng Liu, Jing-Tian Li, Quan Song, Jun Zhuang and Xi-Jing Ning

Crystals 2017, 7(2), 35; https://doi.org/10.3390/cryst7020035 - 15 Feb 2017

Cited by 2 | Viewed by 3829

Abstract

Based on the monolayer growth mode of graphene sheets (2D crystal) by chemical vapor deposition (CVD) on a Cu surface, it should be possible to grow the 2D crystal embedded with single wall carbon nanocones (SWCNC) if nano-conical pits are pre-fabricated on the [...] Read more.

Based on the monolayer growth mode of graphene sheets (2D crystal) by chemical vapor deposition (CVD) on a Cu surface, it should be possible to grow the 2D crystal embedded with single wall carbon nanocones (SWCNC) if nano-conical pits are pre-fabricated on the surface. However, a previous experiment showed that the growing graphene sheet can cross grain boundaries without bending, which seems to invalidate this route for growing SWCNCs. The criterion of Gibbs free energy was applied in the present work to address this issue, showing that the sheet can grow into the valley of a boundary if the boundary has a slope instead of a quarter-turn shape, and SWCNCs can be obtained by this route as long as the lower diameter of the pre-fabricated pit is larger than 1.6 nm and the deposition temperature is higher than 750 K. Full article

(This article belongs to the Special Issue Advances in Computer Simulation Studies on Crystal Growth)

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1980 KiB

Open AccessArticle

Atomistic Modelling of Si Nanoparticles Synthesis

by Giovanni Barcaro, Susanna Monti, Luca Sementa and Vincenzo Carravetta

Crystals 2017, 7(2), 54; https://doi.org/10.3390/cryst7020054 - 13 Feb 2017

Cited by 8 | Viewed by 4709

Abstract

Silicon remains the most important material for electronic technology. Presently, some efforts are focused on the use of Si nanoparticles—not only for saving material, but also for improving the efficiency of optical and electronic devices, for instance, in the case of solar cells [...] Read more.

Silicon remains the most important material for electronic technology. Presently, some efforts are focused on the use of Si nanoparticles—not only for saving material, but also for improving the efficiency of optical and electronic devices, for instance, in the case of solar cells coated with a film of Si nanoparticles. The synthesis by a bottom-up approach based on condensation from low temperature plasma is a promising technique for the massive production of such nanoparticles, but the knowledge of the basic processes occurring at the atomistic level is still very limited. In this perspective, numerical simulations can provide fundamental information of the nucleation and growth mechanisms ruling the bottom-up formation of Si nanoclusters. We propose to model the low temperature plasma by classical molecular dynamics by using the reactive force field (ReaxFF) proposed by van Duin, which can properly describe bond forming and breaking. In our approach, first-principles quantum calculations are used on a set of small Si clusters in order to collect all the necessary energetic and structural information to optimize the parameters of the reactive force-field for the present application. We describe in detail the procedure used for the determination of the force field and the following molecular dynamics simulations of model systems of Si gas at temperatures in the range 2000–3000 K. The results of the dynamics provide valuable information on nucleation rate, nanoparticle size distribution, and growth rate that are the basic quantities for developing a following mesoscale model. Full article

(This article belongs to the Special Issue Advances in Computer Simulation Studies on Crystal Growth)

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1433 KiB

Open AccessArticle

Optical Properties of the Fresnoite Ba₂TiSi₂O₈ Single Crystal

by Chuanying Shen, Huaijin Zhang, Duanliang Wang, Jiyang Wang and Robert I. Boughton

Crystals 2017, 7(2), 53; https://doi.org/10.3390/cryst7020053 - 11 Feb 2017

Cited by 19 | Viewed by 5664

Abstract

In this work, using large-sized single crystals of high optical quality, the optical properties of Ba₂TiSi₂O₈ were systematically investigated, including transmission spectra, refractive indices and nonlinear absorption properties. The crystal exhibits a high transmittance (>84%) over a wide [...] Read more.

In this work, using large-sized single crystals of high optical quality, the optical properties of Ba₂TiSi₂O₈ were systematically investigated, including transmission spectra, refractive indices and nonlinear absorption properties. The crystal exhibits a high transmittance (>84%) over a wide wavelength range from 340 to 2500 nm. The refractive indices in the range from 0.31256 to 1.01398 μm were measured, and Sellmeier’s equations were fitted by the least squares method. The nonlinear absorption properties were studied by using the open-aperture Z-scan technique, with a nonlinear absorption coefficient measured to be on the order of 0.257 cm/GW at the peak power density of 16.4 GW/cm². Such high transmittance and wide transparency indicate that optical devices using the Ba₂TiSi₂O₈crystal can be applied over a wide wavelength range. Furthermore, the small nonlinear absorption observed in Ba₂TiSi₂O₈ will effectively increase the optical conversion efficiency, decreasing the generation of laser damage of the optical device. Full article

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4842 KiB

Open AccessArticle

SRG Inscription in Supramolecular Liquid Crystalline Polymer Film: Replacement of Mesogens

by Shun Mitsui, Shusaku Nagano, Mitsuo Hara and Takahiro Seki

Crystals 2017, 7(2), 52; https://doi.org/10.3390/cryst7020052 - 11 Feb 2017

Cited by 12 | Viewed by 5534

Abstract

The photoinduced surface relief formation via mass transfer upon irradiation with patterned light has long been a subject of extensive investigation. In azobenzene-containing liquid crystalline materials, UV light irradiation that generates the cis isomer leads to the liquid crystal to isotropic photochemical transition. [...] Read more.

The photoinduced surface relief formation via mass transfer upon irradiation with patterned light has long been a subject of extensive investigation. In azobenzene-containing liquid crystalline materials, UV light irradiation that generates the cis isomer leads to the liquid crystal to isotropic photochemical transition. Due to this phase change, efficiency of the mass transfer to generate a surface relief grating (SRG) becomes markedly greater. We have previously indicated that azobenzene-colored SRG-inscribed film can be bleached by removing a hydrogen-bonded azobenzene mesogen. However, this process largely reduces the height feature of the SRG corrugation. Herein, we propose an extended procedure where a colorless mesogen is filled successively after the removal of the azobenzene side chain. The process involves four stages: (i) SRG inscription in a hydrogen-bonded supramolecular azobenzene material; (ii) crosslinking (insolubilization) of the SRG film; (iii) removal of azobenzene mesogen by rinsing with a solvent, and (iv) stuffing the hollow film with a different mesogen. Although the final stuffing stage was insufficient at the present stage, this work demonstrates the possibility and validity of the strategy of mesogen replacement. Full article

(This article belongs to the Special Issue Micro and Nano Patterned Substrates for Liquid Crystal Alignment)

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2397 KiB

Open AccessArticle

Kinetics and Morphology of Flow Induced Polymer Crystallization in 3D Shear Flow Investigated by Monte Carlo Simulation

by Chunlei Ruan

Crystals 2017, 7(2), 51; https://doi.org/10.3390/cryst7020051 - 11 Feb 2017

Cited by 17 | Viewed by 5462

Abstract

To explore the kinetics and morphology of flow induced crystallization of polymers, a nucleation-growth evolution model for spherulites and shish-kebabs is built based on Schneider rate model and Eder model. The model considers that the spherulites are thermally induced, growing like spheres, while [...] Read more.

To explore the kinetics and morphology of flow induced crystallization of polymers, a nucleation-growth evolution model for spherulites and shish-kebabs is built based on Schneider rate model and Eder model. The model considers that the spherulites are thermally induced, growing like spheres, while the shish-kebabs are flow induced, growing like cylinders, with the first normal stress difference of crystallizing system being the driving force for the nucleation of shish-kebabs. A two-phase suspension model is introduced to describe the crystallizing system, which Finitely Extensible Non-linear Elastic-Peterlin (FENE-P) model and rigid dumbbell model are used to describe amorphous phase and semi-crystalline phase, respectively. Morphological Monte Carlo method is presented to simulate the polymer crystallization in 3D simple shear flow. Roles of shear rate, shear time and shear strain on the crystallization kinetics, morphology, and rheology are analyzed. Numerical results show that crystallization kinetics, morphology and rheology in shear flow are qualitatively in agreement with the theoretical, experimental and other numerical works which verifies the validity and effectiveness of our model and algorithm. To our knowledge, this is the first time that a model and an algorithm revealing the details of crystal morphology have been applied to the flow induced crystallization of polymers. Full article

(This article belongs to the Special Issue Advances in Computer Simulation Studies on Crystal Growth)

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734 KiB

Open AccessReview

On the Anionic Group Approximation to the Borate Nonlinear Optical Materials

by Rukang Li

Crystals 2017, 7(2), 50; https://doi.org/10.3390/cryst7020050 - 11 Feb 2017

Cited by 32 | Viewed by 4546

Abstract

In this mini-review type of article, a brief summary of the anionic group approximation as it relates to the borate nonlinear optical (NLO) crystals, an idea firstly proposed by Professor Chen, is presented.The basic idea, calculation method, tabulated coefficients of various common borate, [...] Read more.

In this mini-review type of article, a brief summary of the anionic group approximation as it relates to the borate nonlinear optical (NLO) crystals, an idea firstly proposed by Professor Chen, is presented.The basic idea, calculation method, tabulated coefficients of various common borate, as well as nitrate or carbonate groups, in their ideal geometries will be presented. New practices reveal that those parameters can still give very accurate predicted NLO coefficients for recently found NLO crystals without any adjustment of parameters. Full article

(This article belongs to the Special Issue Nonlinear Optical Crystals 2017—Commemorative Issue in Honor of Professor Chuangtian Chen on the Occasion of his 80th Anniversary)

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Open AccessArticle

Graphene-Hexagonal Boron Nitride Heterostructure as a Tunable Phonon–Plasmon Coupling System

by Sheng Qu, Hongxia Liu, Lu Dong, Lei Wu, Congcong Ma and Shulong Wang

Crystals 2017, 7(2), 49; https://doi.org/10.3390/cryst7020049 - 10 Feb 2017

Cited by 12 | Viewed by 6891

Abstract

The layered van der Waals (vdW) heterostructure, assembled from monolayer graphene, hexagonal boron nitride (h-BN) and other atomic crystals in various combinations, is emerging as a new paradigm with which to attain desired electronic and optical properties. In this paper, we study theoretically [...] Read more.

The layered van der Waals (vdW) heterostructure, assembled from monolayer graphene, hexagonal boron nitride (h-BN) and other atomic crystals in various combinations, is emerging as a new paradigm with which to attain desired electronic and optical properties. In this paper, we study theoretically the mid-infrared optical properties of the vdW heterostructure based on the graphene–h-BN system. The light–matter interaction of this heterostructure system is described by the hyperbolic phonon–plasmon polaritons which originate from the coupling modes of surface plasmon polaritons (SPPs) in graphene with hyperbolic phonon polaritons (HPPs) in h-BN. By numerical simulation, we find that the coupling modes are governed by the Fermi level of monolayer graphene, the thickness of the h-BN slab and the mode excitation sequence of SPPs and HPPs. Moreover, the response of the coupling modes of the graphene–h-BN heterostructure on a noble metal layer is also proposed in this paper. Full article

(This article belongs to the Special Issue Two-Dimensional Materials beyond Graphene and their Van der Waals Heterostructures)

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6971 KiB

Open AccessArticle

Ultrathin Nanocrystalline Magnetic Wires

by Horia Chiriac, Nicoleta Lupu, George Stoian, Gabriel Ababei, Sorin Corodeanu and Tibor-Adrian Óvári

Crystals 2017, 7(2), 48; https://doi.org/10.3390/cryst7020048 - 10 Feb 2017

Cited by 58 | Viewed by 6851

Abstract

The magnetic characteristics of FINEMET type glass-coated nanowires and submicron wires are investigated by taking into account the structural evolution induced by specific annealing all the way from a fully amorphous state to a nanocrystalline structure. The differences between the magnetic properties of [...] Read more.

The magnetic characteristics of FINEMET type glass-coated nanowires and submicron wires are investigated by taking into account the structural evolution induced by specific annealing all the way from a fully amorphous state to a nanocrystalline structure. The differences between the magnetic properties of these ultrathin wires and those of the thicker glass-coated microwires and “conventional” wires with similar structures have been emphasized and explained phenomenologically. The domain wall propagation in these novel nanowires and submicron wires, featuring a combination between an amorphous and a crystalline structure, has also been studied, given the recent interest in the preparation and investigation of new materials suitable for the development of domain wall logic applications. Full article

(This article belongs to the Special Issue Advance in Crystalline Thin Wires)

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1668 KiB

Open AccessArticle

Site Identity and Importance in Cosubstituted Bixbyite In₂O₃

by Karl Rickert, Jeremy Harris, Nazmi Sedefoglu, Hamide Kavak, Donald E. Ellis and Kenneth R. Poeppelmeier

Crystals 2017, 7(2), 47; https://doi.org/10.3390/cryst7020047 - 9 Feb 2017

Cited by 3 | Viewed by 6456

Abstract

The bixbyite structure of In₂O₃ has two nonequivalent, 6-coordinate cation sites and, when Sn is doped into In₂O₃, the Sn prefers the “b-site” and produces a highly conductive material. When divalent/tetravalent cation pairs are [...] Read more.

The bixbyite structure of In₂O₃ has two nonequivalent, 6-coordinate cation sites and, when Sn is doped into In₂O₃, the Sn prefers the “b-site” and produces a highly conductive material. When divalent/tetravalent cation pairs are cosubstituted into In₂O₃, however, the conductivity increases to a lesser extent and the site occupancy is less understood. We examine the site occupancy in the Mg_xIn_2−2xSn_xO₃ and Zn_xIn_2−2xSn_xO₃ systems with high resolution X-ray and neutron diffraction and density functional theory computations, respectively. In these sample cases and those that are previously reported in the M_xIn_2−2xSn_xO₃ (M = Cu, Ni, or Zn) systems, the solubility limit is greater than 25%, ensuring that the b-site cannot be the exclusively preferred site as it is in Sn:In₂O₃. Prior to this saturation point, we report that the M²⁺ cation always has at least a partial occupancy on the d-site and the Sn⁴⁺ cation has at least a partial occupancy on the b-site. The energies of formation for these configurations are highly favored, and prefer that the divalent and tetravalent substitutes are adjacent in the crystal lattice, which suggests short range ordering. Diffuse reflectance and 4-point probe measurements of Mg_xIn_2−xSn_xO₃ demonstrate that it can maintain an optical band gap >2.8 eV while surpassing 1000 S/cm in conductivity. Understanding how multiple constituents occupy the two nonequivalent cation sites can provide information on how to optimize cosubstituted systems to increase Sn solubility while maintaining its dopant nature, achieving maximum conductivity. Full article

(This article belongs to the Special Issue Crystal Structure of Electroceramics)

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Open AccessReview

Recent Progress in Computational Materials Science for Semiconductor Epitaxial Growth

by Tomonori Ito and Toru Akiyama

Crystals 2017, 7(2), 46; https://doi.org/10.3390/cryst7020046 - 9 Feb 2017

Cited by 6 | Viewed by 7132

Abstract

Recent progress in computational materials science in the area of semiconductor epitaxial growth is reviewed. Reliable prediction can now be made for a wide range of problems, such as surface reconstructions, adsorption-desorption behavior, and growth processes at realistic growth conditions, using our ab [...] Read more.

Recent progress in computational materials science in the area of semiconductor epitaxial growth is reviewed. Reliable prediction can now be made for a wide range of problems, such as surface reconstructions, adsorption-desorption behavior, and growth processes at realistic growth conditions, using our ab initio-based chemical potential approach incorporating temperature and beam equivalent pressure. Applications are examined by investigating the novel behavior during the hetero-epitaxial growth of InAs on GaAs including strain relaxation and resultant growth mode depending growth orientations such as (111)A and (001). Moreover, nanowire formation is also exemplified for adsorption-desorption behaviors of InP nanowire facets during selective-area growth. An overview of these issues is provided and the latest achievement are presented to illustrate the capability of the theoretical-computational approach by comparing experimental results. These successful applications lead to future prospects for the computational materials design in the fabrication of epitaxially grown semiconductor materials. Full article

(This article belongs to the Special Issue Advances in Computer Simulation Studies on Crystal Growth)

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3369 KiB

Open AccessReview

Review of the Magnetocaloric Effect in RMnO3 and RMn2O5 Multiferroic Crystals

by Mohamed Balli, Benoit Roberge, Patrick Fournier and Serge Jandl

Crystals 2017, 7(2), 44; https://doi.org/10.3390/cryst7020044 - 8 Feb 2017

Cited by 72 | Viewed by 10726

Abstract

It is known that some of RMnO3 and RMn2O5 (R = rare earth) multiferroic crystals reveal a strong interplay between their magnetic and electric order parameters, paving the way for applications in spintronic technologies. Additionally, recent works have also pointed out their potential [...] Read more.

It is known that some of RMnO3 and RMn2O5 (R = rare earth) multiferroic crystals reveal a strong interplay between their magnetic and electric order parameters, paving the way for applications in spintronic technologies. Additionally, recent works have also pointed out their potential utilization as refrigerants in magnetocaloric cooling systems for cryogenic tasks. In this paper, recent advances regarding the magnetocaloric properties of both RMnO3 and RMn2O5 families of multiferroics are reviewed. With the aim of understanding the RMnO3 and RMn2O5 magnetocaloric features, their structural and magnetic properties are discussed. The physics behind the magnetocaloric effect as well as some of its key thermodynamic aspects are also considered. Full article

(This article belongs to the Special Issue Multiferroics Crystals)

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1924 KiB

Open AccessArticle

Lewis Acid Properties of Tetrel Tetrafluorides—The Coincidence of the σ-Hole Concept with the QTAIM Approach

by Sławomir J. Grabowski

Crystals 2017, 7(2), 43; https://doi.org/10.3390/cryst7020043 - 8 Feb 2017

Cited by 34 | Viewed by 5175

Abstract

Tetrel bond is analysed for a series of ZF₄ (Z = C, Si, Ge) complexes with one and two NH₃ or AsH₃ ligands. The MP2/aug-cc-pVTZ calculations were performed and supported by results of the Quantum Theory of “Atoms in Molecules” [...] Read more.

Tetrel bond is analysed for a series of ZF₄ (Z = C, Si, Ge) complexes with one and two NH₃ or AsH₃ ligands. The MP2/aug-cc-pVTZ calculations were performed and supported by results of the Quantum Theory of “Atoms in Molecules” (QTAIM) and the Natural Bond Orbitals (NBO) approaches. The Z-tetrel atoms of complexes analysed interact through their σ-holes with nitrogen or arsenic Lewis base centres; these interactions correspond to the Z…N/As bond paths according to the QTAIM approach. The QTAIM and NBO results show that these interactions are relatively strong and they possess numerous characteristics of covalent bonds. The theoretical analysis is supported by the discussion on crystal structures which are characterized by the same type interactions. Full article

(This article belongs to the Special Issue Analysis of Halogen and Other σ-Hole Bonds in Crystals)

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3865 KiB

Open AccessArticle

Disassembly of Faceted Macrosteps in the Step Droplet Zone in Non-Equilibrium Steady State

by Noriko Akutsu

Crystals 2017, 7(2), 42; https://doi.org/10.3390/cryst7020042 - 8 Feb 2017

Cited by 12 | Viewed by 5279

Abstract

A Wulff figure—the polar graph of the surface tension of a crystal—with a discontinuity was calculated by applying the density matrix renormalization group method to the p-RSOS model, a restricted solid-on-solid model with a point-contact-type step–step attraction. In the step droplet zone in [...] Read more.

A Wulff figure—the polar graph of the surface tension of a crystal—with a discontinuity was calculated by applying the density matrix renormalization group method to the p-RSOS model, a restricted solid-on-solid model with a point-contact-type step–step attraction. In the step droplet zone in this model, the surface tension is discontinuous around the (111) surface and continuous around the (001) surface. The vicinal surface of 4H-SiC crystal in a Si–Cr–C solution is thought to be in the step droplet zone. The dependence of the vicinal surface growth rate and the macrostep size

〈 n 〉

on the driving force

Δ μ

for a typical state in the step droplet zone in non-equilibrium steady state was calculated using the Monte Carlo method. In contrast to the known step bunching phenomenon, the size of the macrostep was found to decrease with increasing driving force. The detachment of elementary steps from a macrostep was investigated, and it was found that

〈 n 〉

satisfies a scaling function. Moreover, kinetic roughening was observed for

| Δ μ | > Δ μ_{R}

, where

Δ μ_{R}

is the crossover driving force above which the macrostep disappears. Full article

(This article belongs to the Special Issue Advances in Computer Simulation Studies on Crystal Growth)

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11560 KiB

Open AccessReview

Correlation of Crystalline Structure with Magnetic and Transport Properties of Glass-Coated Microwires

by Arcady Zhukov, Mihail Ipatov, Ahmed Talaat, Juan Maria Blanco, Blanca Hernando, Lorena Gonzalez-Legarreta, Joan Josep Suñol and Valentina Zhukova

Crystals 2017, 7(2), 41; https://doi.org/10.3390/cryst7020041 - 8 Feb 2017

Cited by 68 | Viewed by 8047

Abstract

We overviewed the correlation between the structure, magnetic and transport properties of magnetic microwires prepared by the Taylor-Ulitovsky method involving rapid quenching from the melt and drawing of the composite (metallic core, glass coated) wire. We showed that this method can be useful [...] Read more.

We overviewed the correlation between the structure, magnetic and transport properties of magnetic microwires prepared by the Taylor-Ulitovsky method involving rapid quenching from the melt and drawing of the composite (metallic core, glass coated) wire. We showed that this method can be useful for the preparation of different families of magnetic microwires: soft magnetic microwires displaying Giant magnetoimpedance (GMI) effect, semi-hard magnetic microwires, microwires with granular structure exhibiting Giant Magnetoresistance (GMR) effect and Heusler-type microwires. Magnetic and transport properties of magnetic microwires depend on the chemical composition of metallic nucleus and on the structural features (grain size, precipitating phases) of prepared microwires. In all families of crystalline microwires, their structure, magnetic and transport properties are affected by internal stresses induced by the glass coating, depending on the quenching rate. Therefore, properties of glass-coated microwires are considerably different from conventional bulk crystalline alloys. Full article

(This article belongs to the Special Issue Advance in Crystalline Thin Wires)

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30154 KiB

Open AccessArticle

Agglomeration Control during Ultrasonic Crystallization of an Active Pharmaceutical Ingredient

by Bjorn Gielen, Jeroen Jordens, Leen C. J. Thomassen, Leen Braeken and Tom Van Gerven

Crystals 2017, 7(2), 40; https://doi.org/10.3390/cryst7020040 - 8 Feb 2017

Cited by 55 | Viewed by 11866

Abstract

Application of ultrasound during crystallization can efficiently inhibit agglomeration. However, the mechanism is unclear and sonication is usually enabled throughout the entire process, which increases the energy demand. Additionally, improper operation results in significant crystal damage. Therefore, the present work addresses these issues [...] Read more.

Application of ultrasound during crystallization can efficiently inhibit agglomeration. However, the mechanism is unclear and sonication is usually enabled throughout the entire process, which increases the energy demand. Additionally, improper operation results in significant crystal damage. Therefore, the present work addresses these issues by identifying the stage in which sonication impacts agglomeration without eroding the crystals. This study was performed using a commercially available API that showed a high tendency to agglomerate during seeded crystallization. The crystallization progress was monitored using process analytical tools (PAT), including focus beam reflectance measurements (FBRM) to track to crystal size and number and Fourier transform infrared spectroscopy (FTIR) to quantify the supersaturation level. These tools provided insight in the mechanism by which ultrasound inhibits agglomeration. A combination of improved micromixing, fast crystal formation which accelerates depletion of the supersaturation and a higher collision frequency prevent crystal cementation to occur. The use of ultrasound as a post-treatment can break some of the agglomerates, but resulted in fractured crystals. Alternatively, sonication during the initial seeding stage could assist in generating nuclei and prevent agglomeration, provided that ultrasound was enabled until complete desupersaturation at the seeding temperature. FTIR and FBRM can be used to determine this end point. Full article

(This article belongs to the Special Issue Advances in Ultrasound Stimulated Crystallization)

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3347 KiB

Open AccessArticle

Calcined Solution-Based PVP Influence on ZnO Semiconductor Nanoparticle Properties

by Halimah Mohamed Kamari, Naif Mohammed Al-Hada, Elias Saion, Abdul Halim Shaari, Zainal Abidin Talib, Moayad Husein Flaifel and Abdullah Ahmed Ali Ahmed

Crystals 2017, 7(2), 2; https://doi.org/10.3390/cryst7020002 - 8 Feb 2017

Cited by 44 | Viewed by 7286

Abstract

A water-based solution of polyvinylpyrrolidone (PVP) at various concentrations and zinc nitrates were used in conjunction with calcination to produce zinc oxide semiconductor nanoparticles. The extent to which the zinc oxide semiconductor nanoparticles had become crystallized was measured using X-ray diffraction (XRD), whilst [...] Read more.

A water-based solution of polyvinylpyrrolidone (PVP) at various concentrations and zinc nitrates were used in conjunction with calcination to produce zinc oxide semiconductor nanoparticles. The extent to which the zinc oxide semiconductor nanoparticles had become crystallized was measured using X-ray diffraction (XRD), whilst morphological characteristics were determined using scanning electron microscopy (SEM). Transmission electron microscopy (TEM) supported by XRD results were used to evaluate the average particle size. Fourier transform infrared spectroscopy (FT-IR) was then carried out in order to identify the composition phase, since this suggested that the samples contained metal oxide bands and that all organic compounds had been effectively removed after calcination. A UV-VIS spectrophotometer was used to determine the energy band gap and illustrate optical features. Additionally, photoluminescence (PL) spectra revealed that the intensity of photoluminescence decreased with a decrease in particle size. The obtained results have mainly been inclusive for uses by several semiconductor applications in different fields, such as environmental applications and studies, since an absorption process for energy wavelengths could efficiently occur. Full article

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967 KiB

Open AccessReview

Hydrothermal Crystal Growth of Piezoelectric α-Quartz Phase of AO₂ (A = Ge, Si) and MXO₄ (M = Al, Ga, Fe and X = P, As): A Historical Overview

by Olivier Cambon and Julien Haines

Crystals 2017, 7(2), 38; https://doi.org/10.3390/cryst7020038 - 4 Feb 2017

Cited by 11 | Viewed by 8004

Abstract

Quartz is the most frequently used piezoelectric material. Single crystals are industrially grown by the hydrothermal route under super-critical conditions (150 MPa-623 K). This paper is an overview of the hydrothermal crystal growth of the AO₂ and MXO₄ α-quartz [...] Read more.

Quartz is the most frequently used piezoelectric material. Single crystals are industrially grown by the hydrothermal route under super-critical conditions (150 MPa-623 K). This paper is an overview of the hydrothermal crystal growth of the AO₂ and MXO₄ α-quartz isotypes. All of the studies on the crystal growth of this family of materials enable some general and schematic conclusions to be made concerning the influence of different parameters for growing these α-quartz-type materials with different chemical compositions. The solubility of the material is the main parameter, which governs both thermodynamic parameters, P and T, of the crystal growth. Then, depending on the chemistry of the α-quartz-type phase, different parameters have to be considered with the aim of obtaining the basic building units (BBU) of the crystals in solution responsible for the growth of the α-quartz-type phase. A schematic method is proposed, based on the main parameter governing the crystal growth of the α-quartz phase. All of the crystal growth processes have been classified according to four routes: classical, solute-induced, seed-induced and solvent-induced crystal growth. Full article

(This article belongs to the Special Issue Crystal Growth for Optoelectronic and Piezoelectric Applications)

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13316 KiB

Open AccessArticle

Crystal Structure of the 23S rRNA Fragment Specific to r-Protein L1 and Designed Model of the Ribosomal L1 Stalk from Haloarcula marismortui

by Azat Gabdulkhakov, Svetlana Tishchenko, Alisa Mikhaylina, Maria Garber, Natalia Nevskaya and Stanislav Nikonov

Crystals 2017, 7(2), 37; https://doi.org/10.3390/cryst7020037 - 2 Feb 2017

Cited by 6 | Viewed by 6576

Abstract

The crystal structure of the 92-nucleotide L1-specific fragment of 23S rRNA from Haloarcula marismortui (Hma) has been determined at 3.3 Å resolution. Similar to the corresponding bacterial rRNA fragments, this structure contains joined helix 76-77 topped by an approximately globular structure formed by [...] Read more.

The crystal structure of the 92-nucleotide L1-specific fragment of 23S rRNA from Haloarcula marismortui (Hma) has been determined at 3.3 Å resolution. Similar to the corresponding bacterial rRNA fragments, this structure contains joined helix 76-77 topped by an approximately globular structure formed by the residual part of the L1 stalk rRNA. The position of HmaL1 relative to the rRNA was found by its docking to the rRNA fragment using the L1-rRNA complex from Thermus thermophilus as a guide model. In spite of the anomalous negative charge of the halophilic archaeal protein, the conformation of the HmaL1-rRNA interface appeared to be very close to that observed in all known L1-rRNA complexes. The designed structure of the L1 stalk was incorporated into the H. marismortui 50S ribosomal subunit. Comparison of relative positions of L1 stalks in 50S subunits from H. marismortui and T. thermophilus made it possible to reveal the site of inflection of rRNA during the ribosome function. Full article

(This article belongs to the Special Issue Recent Advances in Protein Crystallography)

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3876 KiB

Open AccessArticle

Reversed Crystal Growth of Calcite in Naturally Occurring Travertine Crust

by Heather F. Greer, Wuzong Zhou and Li Guo

Crystals 2017, 7(2), 36; https://doi.org/10.3390/cryst7020036 - 28 Jan 2017

Cited by 10 | Viewed by 10222

Abstract

A microstructural investigation by electron microscopy on a travertine specimen collected from Munigou National Park, Sichuan Province, China revealed evidence of a non-classical reversed crystal growth route previously only discovered in synthetic materials. Examination of the travertine specimen suggests that the presence of [...] Read more.

A microstructural investigation by electron microscopy on a travertine specimen collected from Munigou National Park, Sichuan Province, China revealed evidence of a non-classical reversed crystal growth route previously only discovered in synthetic materials. Examination of the travertine specimen suggests that the presence of organic matter initiates the oriented aggregation of calcite nanocrystallites. Surface re-crystallisation of the aggregates leads to a single crystalline rhombohedral shell with a polycrystalline core. This core-shell structure carries a strong resemblance to synthetic calcite prepared in the presence of chitosan, where the growth of calcite was found to follow the so-called reversed crystal growth process. It is proposed that the similar roles of biomolecules in naturally occurring travertine and chitosan in the synthetic system are based on their isoelectric points and the polymerizable property of long chain chemical structures. This study is important so that the structural similarities between naturally occurring biominerals and biomimetic materials can be further understood. Full article

(This article belongs to the Special Issue Mesocrystals and Hierarchical Structures)

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1519 KiB

Open AccessArticle

Simple Metal and Binary Alloy Phases Based on the fcc Structure: Electronic Origin of Distortions, Superlattices and Vacancies

by Valentina F. Degtyareva and Nataliya S. Afonikova

Crystals 2017, 7(2), 34; https://doi.org/10.3390/cryst7020034 - 28 Jan 2017

Cited by 8 | Viewed by 7078

Abstract

Crystal structures of simple metals and binary alloy phases based on the face-centered cubic (fcc) structure are analyzed within the model of Fermi sphere–Brillouin zone interactions to understand the stability of the original cubic structure and derivative structures with distortions, superlattices [...] Read more.

Crystal structures of simple metals and binary alloy phases based on the face-centered cubic (fcc) structure are analyzed within the model of Fermi sphere–Brillouin zone interactions to understand the stability of the original cubic structure and derivative structures with distortions, superlattices and vacancies. Examination of the Brillouin–Jones configuration in relation to the nearly-free electron Fermi sphere for several representative phases reveals significance of the electron energy contribution to the phase stability. Representation of complex structures in the reciprocal space clarifies their relationship to the basic cubic cell. Full article

(This article belongs to the Section Crystal Engineering)

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2476 KiB

Open AccessArticle

Synthesis, Crystal Structure, and Luminescent Property of a Cd(II) Coordination Polymer with a N-Nicotinoylglycine Ligand

by Xi-Shi Tai, Xin Wang and Peng-Fei Li

Crystals 2017, 7(2), 33; https://doi.org/10.3390/cryst7020033 - 25 Jan 2017

Cited by 12 | Viewed by 4279

Abstract

A new 1D Cd(II) coordination polymer, [{CdL₂(H₂O)}·(H₂O)₃]_n (HL = N-nicotinoylglycine), has been synthesized by the assembly of Cd(NO₃)₂·4H₂O with N-nicotinoylglycine, and its composition was determined by [...] Read more.

A new 1D Cd(II) coordination polymer, [{CdL₂(H₂O)}·(H₂O)₃]_n (HL = N-nicotinoylglycine), has been synthesized by the assembly of Cd(NO₃)₂·4H₂O with N-nicotinoylglycine, and its composition was determined by elemental analysis, infrared, and X-ray single-crystal diffraction analysis. In this complex, the Cd(II) is seven-coordinated by two N atoms of two N-nicotinoylglycine anions, four O atoms of two N-nicotinoylglycine anions, and one O atom of a coordinated water molecule. The complex forms a 1D looped coordination polymer by the bridging of the N-nicotinoylglycine anion. The luminescent property of the N-nicotinoylglycine ligand and the Cd(II) coordination polymer has also been studied. Full article

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Crystals, Volume 7, Issue 2 (February 2017) – 31 articles

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