Class Of Crystals Research Articles

A three-dimensional twisted phononic crystal with omnidirectional bandgap based on inertial amplification by utilizing translation-rotation coupling

This work presents the design, manufacture, and experimental testing of a three-dimensional twisted phononic crystal made of a single-phase material. A broad, omnidirectional bandgap with continuously strong attenuation from 601 to 1504 Hz has been achieved, yet the filling ratio of the unit cell is just 22.4%. The theoretical study demonstrates that the inertial amplification based on the translation-rotation coupling is the cause of the bandgap. The translation-rotation coupling enables this phononic crystal to possess two stages of amplification. The tunability of the bandgap can be achieved in the first stage by intelligently regulating the contour of the lumped masses under the limitations of the quasi-constant stiffness and constant mass of the unit cell. The second stage allows the tilt angle of the ligaments to become a constantly tunable variable of the bandgap. This research comprehensively illuminates the 3D twisted phononic crystal based on inertial amplification and the approaches for tuning the bandgap in this class of phononic crystals.

Ice crystal images from optical array probes: classification with convolutional neural networks

Abstract. Although airborne optical array probes (OAPs) have existed for decades, our ability to maximize extraction of meaningful morphological information from the images produced by these probes has been limited by the lack of automatic, unbiased, and reliable classification tools. The present study describes a methodology for automatic ice crystal recognition using innovative machine learning. Convolutional neural networks (CNNs) have recently been perfected for computer vision and have been chosen as the method to achieve the best results together with the use of finely tuned dropout layers. For the purposes of this study, The CNN has been adapted for the Precipitation Imaging Probe (PIP) and the 2DS Stereo Probe (2DS), two commonly used probes that differ in pixel resolution and measurable maximum size range for hydrometeors. Six morphological crystal classes have been defined for the PIP and eight crystal classes and an artifact class for the 2DS. The PIP and 2DS classifications have five common classes. In total more than 8000 images from both instruments have been manually labeled, thus allowing for the initial training. For each probe the classification design tries to account for the three primary ice crystal growth processes: vapor deposition, riming, and aggregation. We included classes such as fragile aggregates and rimed aggregates with high intra-class shape variability that are commonly found in convective clouds. The trained network is finally tested through human random inspections of actual data to show its real performance in comparison to what humans can achieve.

Features of phase equilibria and properties of phases in the Sb-Sm-Se system

The purpose of the paper is to establish the position of the tie-lines in the Sb-Sm-Se system at 450 ​°C and 620 ​°C, to determine the optical band gap of the phases.The Sb component is in equilibrium with the γ-Sm2Se3-X-Sm3Se4 (ST Th3P4) solid solution region with α-Sm2Se3. A continuous solid solution forms between the SmSb and SmSe (ST NaCl) phases, with which the Sm3Se4 and Sm4Sb3 phases are in equilibrium. The SmSb-Sm3Se4, Sm3Se4-SmSb2, SmSe-Sm3Sb2 phases are also in equilibrium.In the Sb–Sm2Se3–Se system at 450°С, the tie-line passes between the Sb2Se3–Sm2Se3, Sb2Se3-SmSe1.9 phases.In the Sb–Se system based on Sb2Se3, a solid solution of the subtraction type Sb2-X□XSe3 (X ​= ​0–0.04) is formed. In the Sb-Sm-Se system, there is a solid solution of the substitution type along the cuts from Sb2Se3 to the Sm2Se3 (7 ​mol. % Sm2Se3), SmSe1.9 (4 ​mol. % SmSe1.9) phases. The extreme compositions of solid solutions have a peritectic point.Due to the change in the position of the tie-lines in the Sb–Sm2Se3–Se system at 620 ​°C, additional phases appear in the equilibrium samples from the Sb2Se3–Sm2Se3 section (annealing at 450 ​°C) when heated above 620 ​°C: Sb, SmSe1.9.The optical band gap of the phases is: Sb2-xSmxSe3 solid solution 1.17–1.19 ​eV, α-Sm2Se3 1.62 ​eV. Optical properties of incommensurate SmSe1.9 crystal that were investigated for the first time for this class of crystals indicate complex electronic structure that can be characterized as a multi band gap one, with at least two values of the band gap, 1.08 and 1.68 ​eV. Using optical spectroscopy, Sm ions in SmSe1.9 are proved to be predominantly in 3+ oxidation state.Previously, the formation of ternary compounds in the system was reported in the literature. Carefully conducted research allows us to assert their absence.

A verified open-access AI-based chemical microparticle image database for in-situ particle visualization and quantification in multi-phase flow

Deep learning-based image segmentation and classification had been previously proposed for the in-situ measurement of microcrystal size and shape, which showed great potential to expand as a process analytical technology (PAT) to chemical multi-phase flow processes. In this study, an open-access chemical microparticle image database (open-CMD) was established containing particle agglomerations (A), bubbles (B), crystals (C), and droplets (D) in various chemical multi-phase flow scenarios. The advanced neural network, Mask R-CNN, coupled with 2,500 labeled images containing more than 50,000 labeled particles in open-CMD, was trained to build the ability of target particle segmentation and classification. The training results indicated that a data augmentation strategy could significantly improve the accuracy (<3.8 % average precision) of the trained models, which were named MicropNet+ and MicropNet according to whether the augmented data was used for training or not. Based on the superior capability of MicropNet+, multidimensional particle descriptors were extracted, and further, the degree of agglomeration and agglomeration distribution were defined and quantified. Then, two classical multi-phase flow processes, crystallization and emulsification, were analyzed using the MicropNet+ model, in which the agglomeration degree and distribution (Cin A) of succinic acid crystals and the relative number and diameter (Deq) of droplets were analyzed quantitatively under different operations conditions. It was concluded that the well-trained MicropNet+ model has high accuracy and efficiency in microparticle segmentation and classification. At last, the open-CMD database and the MicropNet+ model were released to inspire potential applications in chemical multi-phase flow areas.

Research on Mesoscale Nucleation and Growth Processes in Solution Crystallization: A Review

In recent studies, the existence of mesoscale precursors has been confirmed in crystallization. Different from the classical crystallization theory, which only considers the sequential attachment of basic monomers (atoms, ions, or molecules), the nonclassical crystallization process involving precursors such as prenucleation clusters, nanoparticles, and mesocrystals is more complicated. The mesoscale structure is important for the quantitative description and directional regulation of the solution crystallization process. It is necessary to explore the mechanism by the mesoscale scientific research methods on the base of traditional chemical engineering and process system engineering research methods. Therefore, the paper reviews several representative nonclassical nucleation and growth theories, mainly including two-step nucleation theory, prenucleation clusters theory, particle agglomeration theory, amorphous precursor growth theory, particle attachment growth theory and mesocrystal growth theory. Then, the mesoscale structure and its spatiotemporal dynamic behavior are discussed, and the application of the EMMS model in the nucleation and growth process is analyzed. Finally, we put forward our views on the prospect of the paradigms and theoretical innovations of using mesoscale methods in crystal nucleation and growth.

Research on Circularly Polarized Luminescent and Clustering-Triggered Emission Properties of Cholesteryl Benzoate

Circularly polarized luminescence (CPL) materials have attracted intensive attention due to their exceptional photophysical properties. However, it has been rarely reported in the field of nontraditional luminescence. It is of great significance to construct circularly polarized luminescent materials with atypical luminescent groups without traditional conjugated structures. Cholesteryl benzoate is a classical cholesteric liquid crystal, and we coincidentally find that it shows clustering-triggered emission behavior in recent studies, which means that cholesteryl benzoate can emit circularly polarized light at the cholesteric liquid crystal phase. Therefore, we synthesized cholesteryl benzoate and studied its photophysical properties in detail. The findings show that cholesteryl benzoate shows triggered emission behavior. The research results suggest that the emission behavior of cholesteric benzoate shows concentration-enhanced emission, aggregation-induced emission (AIE), excitation wavelength dependence, and low-temperature phosphorescence luminescence characteristics. The solid-state circularly polarized luminescence (CPL) property of cholesteryl benzoate quenched by the cholesteric phase was also studied, and the measured luminescence asymmetry factor (glum) could achieve −2.6 × 10–3. In addition, we also simulated the luminescence mechanism of cholesteryl benzoate by theoretical calculation.

Chiral Liquid Crystalline Properties of Cellulose Nanocrystals: Fundamentals and Applications.

By using an independent self-assembly process that is occasionally controlled by evaporation, cellulose nanocrystals (CNCs) may create films (pure or in conjunction with other materials) that have iridescent structural colors. The self-forming chiral nematic structures and environmental safety of a new class of photonic liquid crystals (LCs), referred to as CNCs and CNC-embedded materials, make them simple to make and treat. The structure of the matrix interacts with light to give structural coloring, as opposed to other dye pigments, which interact with light by adsorption and reflection. Understanding how CNC self-assembly constructs structures is vital in several fields, including physics, science, and engineering. To constructure this review, the colloidal characteristics of CNC particles and their behavior during the formation of liquid crystals and gelling were studied. Then, some of the recognized applications for these naturally occurring nanoparticles were summarized. Different factors were considered, including the CNC aspect ratio, surface chemistry, concentration, the amount of time needed to produce an anisotropic phase, and the addition of additional substances to the suspension medium. The effects of alignment and the drying process conditions on structural changes are also covered. The focus of this study however is on the optical properties of the films as well as the impact of the aforementioned factors on the final transparency, iridescent colors, and versus the overall response of these bioinspired photonic materials. Control of the examined factors was found to be necessary to produce reliable materials for optoelectronics, intelligent inks and papers, transparent flexible support for electronics, and decorative coatings and films.

A comprehensive view of metallocycles in Pt(η3–P1X1P2)(Y), derivatives-structural aspects

This review covers over one hundred Pt(II) complexes of the compositions Pt(η3–P1X1P2)(Y), (X1 = O1L, N1L, C1L, B1L, S1L or Si1L) and (Y = H, F, Cl, Br, I, O2L, N2L, C2L, or P3L). These complexes crystallized in five crystal classes: monoclinic (60 examples), triclinic (36 examples), orthorhombic (13 examples), trigonal (1 example) and tetragonal (1 example). Each heterotridentate organodiphosphine creates two metallocyclic rings with a common X1 atom. There are fourteen types of metallocycles from which the P1C2X1C2P2 is most common. The structural parameters (Pt-L, L-Pt-L) are analyzed and discussed with attention to the distortion of a square-planar geometry about the Pt(II) atoms as well as of trans-influence.

Al – Ti – B master alloys: structure formation in modified alloys

This paper provides an overview of existing grain refinement mechanisms and describes the solidification kinetics typical of alloys modified with the Al &ndash; Ti &ndash; B system. Of practical interest are intermetallic compounds of the binary Al &ndash; Ti system, the state diagram of which requires further study. It was found that, with titanium concentrations being low, the behaviour of the system is influenced by peritectic reaction leading to &alpha;-grains of aluminium forming on titanium aluminide particles (TiAl3). A unique feature of the Al &ndash; Ti system is that, compared with other alloys, it has the highest limited growth rate Q, which explains the high grain refinement performance. Microparticles of titanium diboride (TiB2) that form in the liquid state of the Al &ndash; Ti &ndash; B system act as nucleation centres for the intermediate phase of TiAl3. At the same time, TiAl3 was found to display metastable properties and it dissolves as aluminium solidifies. The classical crystallization theory defines the importance of heterogeneous substrates that help grain nucleation by lowering the threshold energy. According to the heterogeneous nucleation theory, supercooling tends to increase dramatically during grain nucleation as the discrepancy rises between the crystal lattice of the solid body and that of the substrate. In terms of constitutional supercooling, it takes lower supercooling for grain nucleation on a particle. The contributing factors include a lower rate of latent heat release and low grain growth rates. As the master alloy was introduced in the melt, the authors observed reduced modification efficiency (with the concentration &gt;1.5 %) and dropped solubility of Ti in the presence of Si. Long soaking times would lead to the master alloy gradually lose its effect. The authors also considered how the properties of master alloys can be enhanced. Thus, they looked at breaking up TiAl3 by means of plastic deformation and deagglomerating TiB2 particles by contactless mixing.

A semi-supervised deep-learning approach for automatic crystal structure classification.

The structural solution problem can be a daunting and time-consuming task. Especially in the presence of impurity phases, current methods, such as indexing, become more unstable. In this work, the novel approach of semi-supervised learning is applied towards the problem of identifying the Bravais lattice and the space group of inorganic crystals. The reported semi-supervised generative deep-learning model can train on both labeled data, i.e. diffraction patterns with the associated crystal structure, and unlabeled data, i.e. diffraction patterns that lack this information. This approach allows the models to take advantage of the troves of unlabeled data that current supervised learning approaches cannot, which should result in models that can more accurately generalize to real data. In this work, powder diffraction patterns are classified into all 14 Bravais lattices and 144 space groups (the number is limited due to sparse coverage in crystal structure databases), which covers more crystal classes than other studies. The reported models also outperform current deep-learning approaches for both space group and Bravais lattice classification using fewer training data.

Constitutive modeling of three-dimensional monoatomic linear elastic multilattices

While simple lattices realize only the seven holohedral crystal classes, multilattices can realize all 32 crystal classes in three dimensions. For classical linear elasticity, from the constitutive point of view, the multilattice structure necessitates dependence of the energy apart from the strain tensor on the shift vectors as well. We give a generic expression of the energy for (n + 1) monoatomic multilattices for all 32 crystal classes. We then focus on monoatomic 2-lattices and give the appropriate expression for the energy for all 29 types. The and phases of quartz can be viewed as realizations of a 3-lattice; we lay down expressions for the energy for both its phases. Our framework is valid for the geometrically and materially linear regime.

Wave interaction coefficients for a cubic crystal

We study wave interaction coefficients in elastic solids. They describe locally on a quadratically nonlinear level which waves interact and measure how strong the interactions are. We derive general formulas for these coefficients in an arbitrary anisotropic material expressing them in terms of the second and the third derivatives of the strain energy. To illustrate our results, we analyse the most symmetric class of cubic crystals calculating the coefficients at the zero constant states. We first investigate the geometrically nonlinear and materially linear solid and then we study the influence of material nonlinearities on the interaction coefficients. The obtained formulas are expressed in terms of elastic constants.

Nanoscale Structure of Langmuir-Blodgett Film of Bent-Core Molecules.

Bent-core mesogens (BCMs) are a class of thermotropic liquid crystals featuring several unconventional properties. However, the interpretation and technological exploitation of their unique behavior have been hampered by the difficulty of controlling their anchoring at surfaces. To tackle this issue, we report the nanoscale structural characterization of BCM films prepared using the Langmuir–Blodgett technique. Even though BCMs are quite different from typical amphiphilic molecules, we demonstrate that stable molecular films form over water, which can then be transferred onto silicon substrates. The combination of Brewster angle microscopy, atomic force microscopy, and X-ray reflectivity measurements shows that the molecules, once transferred onto a solid substrate, form a bilayer structure with a bottom layer of flat molecules and an upper layer of upright molecules. These results suggest that Langmuir–Blodgett films of BCMs can provide a useful means to control the alignment of this class of liquid crystals.

Performance of Dispersion-Inclusive Density Functional Theory Methods for Energetic Materials.

Molecular crystals of energetic materials (EMs) are denser than typical molecular crystals and are characterized by distinct intermolecular interactions between nitrogen-containing moieties. To assess the performance of dispersion-inclusive density functional theory (DFT) methods, we have compiled a data set of experimental sublimation enthalpies of 31 energetic materials. We evaluate the performance of three methods: the semilocal Perdew-Burke-Ernzerhof (PBE) functional coupled with the pairwise Tkatchenko-Scheffler (TS) dispersion correction, PBE with the many-body dispersion (MBD) method, and the PBE-based hybrid functional (PBE0) with MBD. Zero-point energy contributions and thermal effects are described using the quasi-harmonic approximation (QHA), including explicit treatment of thermal expansion, which we find to be non-negligible for EMs. The lattice energies obtained with PBE0+MBD are the closest to experimental sublimation enthalpies with a mean absolute error of 9.89 kJ/mol. However, the state-of-the-art treatment of vibrational and thermal contributions makes the agreement with experiment worse. Pressure-volume curves are also examined for six representative materials. For pressure-volume curves, all three methods provide reasonable agreement with experimental data with mean absolute relative errors of 3% or less. Most of the intermolecular interactions typical of EMs, namely nitro-amine, nitro-nitro, and nitro-hydrogen interactions, are more sensitive to the choice of the dispersion method than to the choice of the exchange-correlation functional. The exception is π-π stacking interactions, which are also very sensitive to the choice of the functional. Overall, we find that PBE+TS, PBE+MBD, and PBE0+MBD do not perform as well for energetic materials as previously reported for other classes of molecular crystals. This highlights the importance of testing dispersion-inclusive DFT methods for diverse classes of materials and the need for further method development.

Quantum dynamics of dissipative Kerr solitons

Dissipative Kerr solitons arising from parametric gain in ring microresonators are usually described within a classical mean-field framework. Here, we develop a quantum-mechanical model of dissipative Kerr solitons in terms of the Lindblad master equation and study the model via the truncated Wigner method, which accounts for quantum effects to leading order. We show that, within this open quantum system framework, the soliton experiences a finite coherence time due to quantum fluctuations originating from losses. Reading the results in terms of the theory of open quantum systems allows us to estimate the Liouvillian spectrum of the system. It is characterized by a set of eigenvalues with a finite imaginary part and a vanishing real part in the limit of vanishing quantum fluctuations. This feature shows that dissipative Kerr solitons are a specific class of dissipative time crystals.

Thermally nonlinear non-Fourier piezoelectric thermoelasticity problems with temperature-dependent elastic constants and thermal conductivity and nonlinear finite element analysis

In non-isothermal conditions, numerous experimental and theoretical investigations reveal that the elastic constants and thermal conductivity in piezoelectric solids depend on temperature distribution. This work aims to investigate thermally nonlinear non-Fourier piezoelectric thermoelasticity problems with temperature-dependent elastic constants and thermal conductivity. The nonlinear time-domain finite element method is developed to directly solve nonlinear finite element governing equations, which maximally avoids the precision losses within the applications of the integrated transformation method. As a numerical example, the developed method is applied to analyze nonlinear transient thermo-electromechanical responses of a two-dimensional orthotropic piezoelectric plate of crystal class mm2. The achieved results reveal that temperature-dependent thermal conductivity and elastic constants remarkably affect the structural dynamic responses, whilst thermal wave or elastic wave will travel faster and the electrical energy harvesting ability is significantly elevated.

Low sintering temperature, temperature-stable scheelite structured Bi[V1−x (Fe1/3W 2/3)x]O4 microwave dielectric ceramics

Low sintering temperature Bi[V1−x(Fe1/3W2/3)x]O4 (BVFWx) (0.02 ≤ x ≤ 0.08) ceramics have been prepared by solid-state reaction. Compositions with 0.02 ≤ x ≤ 0.08 were scheelite-structure, but distortion of [BO4] tetrahedra decreased with increase in x. Although the crystal class remained monoclinic, the phase transition temperature (TC) decreased from 255 ℃ (BV) to 51 ℃ (BVFW0.08), suggesting that higher concentrations of (Fe1/3W2/3) would result in the stabilization of tetragonal scheelite at room temperature. The decrease in the [BO4] distortion additionally resulted in a large reduction in the magnitude of the temperature coefficient of resonant frequency (TCF) with near-zero values obtained by sintering BVFW0.08:2BVFW0.06 at 780 °C to give TCF ≈ −5.9 ppm / °C, relative permittivity εr ≈ 77.4, and microwave quality factor, Q × f ≈ 8100 GHz (@ ~ 4.3 GHz). These promising microwave dielectric properties coupled with the low sintering temperature suggest that BVFWx ceramics are of interest in low-temperature cofired ceramic (LTCC) technology, and for monolithic resonator and filter applications.

Synthesis and Liquid Crystalline Properties of Low Molecular Weight Bis- Chalcone Compounds.

In this paper, we report on the synthesis and liquid crystalline properties of some low molecular weight bis-chalcone compounds derived from acetone, cyclopentanone and cyclohexanone mesogenic cores. Structurally bis-chalcones belong to a broader family of chalcone compounds. Chalcone is a compound that consists of two aromatic rings linked by an unsaturated α, β-ketone. Liquid crystalline chalcones are prepared by aliphatic chain substituents on two aromatic rings. Chalcones are well studied for their mesomorphic properties. Compared to a large number of chalcone based LCs reported, only a few articles have been published on the mesomorphic properties of bis-chalcone compounds. The target compounds of the present study varied not only in their central core but also in number and position of terminal aliphatic chain substitution-a key structural unit in deciding the liquid crystalline properties of a compound. All target compounds were synthesized in good yield by base catalyzed Claisen-Schmidt condensation reaction. Molecular structures were confirmed by FT-IR, 1H NMR, 13C NMR, and mass spectroscopic methods. Liquid crystalline property of these compounds was evaluated using polarizing optical microscopy and differential scanning calorimetry. Although none of the acetone based compounds exhibited mesomorphism, cyclopentanone and cyclohexanone based compounds with octyloxy chain at para position on either side of the dibenzylidine ring stabilized liquid crystalline smectic (SmA and SmC) and nematic (N) phases. The observed structure-liquid crystalline property relationship was explained by structural analysis of molecules using DFT calculations. Considering the inherent photoluminescence nature of the chalcone moiety, a preliminary study was carried out on a selected compound to reveal its fluorescence property. Our study brings about an important structure-liquid crystalline property relationship in a relatively unexplored class of bis-chalcone liquid crystals.

Dynamical dimensional reduction in multivalued Hamiltonians

Several interesting physical systems, such as the Lovelock extension of general relativity in higher dimensions, classical time crystals, $k$-essence fields, Horndeski theories, compressible fluids, and nonlinear electrodynamics, have apparent ill-defined sympletic structures, due to the fact that their Hamiltonians are multivalued functions of the momenta. In this paper, the dynamical evolution generated by such Hamiltonians is described as a degenerate dynamical system, whose sympletic form does not have a constant rank, allowing novel features and interpretations not present in previous investigations. In particular, it is shown how the multivaluedness is associated with a dynamical mechanism of dimensional reduction, as some degrees of freedom turn into gauge symmetries when the system degenerates.

Molecular crystals with a sole bearing contact: structural classes and statistical data

Abstract All the structural classes (SCs) of molecular crystals, which are possible to be formed by a sole intermolecular bearing contact, are derived from 1,1- and 2,1-transitive nets. There are 160 (167 including enantiomorphic pairs) monosystemic SCs (in which the molecules occupy one crystallographic orbit) and 244 (248) bisystemic SCs (in which the molecules occupy two crystallographic orbits), i.e. 404 (411) SCs in all. These are the only SCs which can correspond to a homodesmic crystal structure, either organic, or inorganic, in which the structural units are bonded in a single way. Statistical investigation of the Cambridge Structural Database (CSD) shows that ∼1% of monosystemic molecular crystals can be formed by a sole intermolecular bearing contact.