Class Of Crystals Research Articles

Nonclassical and Classical Crystallization: The Formation of Spindle-Shaped CaCO3 Covered with Abundant Nanoscale Rhombic Calcite Subunits

As an essential inorganic material, calcium carbonate (CaCO3) is one of the most abundant minerals in nature, whose preparation by the carbonation of calcium hydroxide [Ca(OH)2] suspension involves complex physical and chemical processes due to the presence of gas–solid–liquid phases. It is challenging to accurately predict the final morphology of CaCO3. In this paper, a novel spindle-shaped CaCO3 covered with a mass of nanoscale rhombic calcite subunits was prepared via the carbonation method. This structure was mainly formed by the aggregation of nanoparticles in the pre-reaction stage and turned into a classical ion–ion growth process at the stage of the late reaction. During the pre-reaction period, solid Ca(OH)2 kept the solution supersaturated and made the aggregation of nanoparticles dominate and assemble to form the nanochains of CaCO3. Subsequently, the aggregation of nanochains formed a dumbbell shape, which was accompanied by the recrystallization of nanoparticles inside aggregates to create an ordered single-crystal spindle structure. Finally, the concentration of Ca(OH)2 decreased, and a layer of nanoscale rhombic calcite subunits grew on the surface of spindle CaCO3. This work will provide new insights into the industrial preparation of CaCO3 with controlled morphology and contribute to understanding the biomineralization of aggregation-based growth in aqueous solutions.

Molecular Modification of Zeolites with Cold Atmospheric-Pressure Plasma Jet: A Green and Facile Strategy

Widespread applications of zeolites demand the optimization of crystal size and morphology. Crystal growth modifiers (CGMs) have been proved effective for zeolite rational design, but the additional chemicals raise environmental and safety concerns. Herein, the industry-ready technique of cold atmospheric-pressure plasma jet (CAPPJ) was employed to induce reactive plasma species as green and eco-friendly CGMs. The synthesis mixtures of three aluminosilicate zeolites with assorted Si/Al ratios (SAR), channel dimensionalities, and pore apertures (i.e., MFI, LTA, and LTL framework types) were first subjected to Ar-CAPPJ treatment for up to 30 min during the aging period. Apparent size and shape modifications were successfully achieved for the resulting crystals with the emergence of rounded surfaces implying surface roughening at the molecular level. For the silicoaluminophosphate SAPO-34 (CHA type), the introduction of plasma CGMs was found to propel a phase transformation, promoting the crystallization of SAPO-18 (AEI type) impurity with reduced framework density. Experimental observations seem to suggest that the classical model of CGMs attaching to selected crystal surfaces is less likely to happen. Whereas, the investigation of zeolite L dispersions revealed enhanced concentrations and altered physicochemical properties of soluble species and amorphous precursors, alluding to the potential functional mechanism (s) of plasma CGMs. As a plausible technique to generate green and versatile CGMs, the impacts of CAPPJ on zeolite crystallization are systematically investigated for the first time, promoting the understanding of classical and nonclassical crystallization phenomena during zeolite synthesis.

Analogs of Rashba-Edelstein effect from density functional theory

Studies of structure-property relationships in spintronics are essential for the design of materials that can fill specific roles in devices. For example, materials with low symmetry allow unconventional configurations of charge-to-spin conversion, which can be used to generate efficient spin-orbit torques. Here, we explore the relationship between crystal symmetry and geometry of the Rashba-Edelstein effect (REE) that causes spin accumulation in response to an applied electric current. Based on a symmetry analysis performed for 230 crystallographic space groups, we identify classes of materials that can host conventional or collinear REE. Although transverse spin accumulation is commonly associated with the so-called ``Rashba materials'', we show that the presence of specific spin texture does not easily translate to the configuration of REE. More specifically, bulk crystals may simultaneously host different types of spin-orbit fields, depending on the crystallographic point group and the symmetry of the specific $k$ vector, which, averaged over the Brillouin zone, determine the direction and magnitude of the induced spin accumulation. To explore the connection between crystal symmetry, spin texture, and the magnitude of REE, we perform first-principles calculations for representative materials with different symmetries. We believe that our results will be helpful for further computational and experimental studies, as well as the design of spintronics devices.

Uncertainty analysis of single- and multiple-size-class frazil ice models

Abstract. The formation of frazil ice in supercooled waters has been extensively studied, both experimentally and numerically, in recent years. Numerical models, with varying degrees of complexity, have been proposed; these are often based on many parameters, the values of which are uncertain and difficult to estimate. In this paper, an uncertainty analysis of two mathematical models that simulate supercooling and frazil ice formation is carried out within a probabilistic framework. The two main goals are (i) to provide quantitative insight into the relative importance of contributing uncertain parameters, to help identify parameters for optimal calibration, and (ii) to compare the output scatter of frazil ice models with single and multiple crystal size classes. The derivation of single- and multi-class models is presented in light of recent work, their numerical resolution is discussed, and a list of the main uncertain parameters is proposed. An uncertainty analysis is then carried out in three steps. Parameter uncertainty is first quantified, based on recent field, laboratory and numerical studies. Uncertainties are then propagated through the models using Monte Carlo simulations. Finally, the relative influence of uncertain parameters on the output time series – i.e., the total frazil volume fraction and water temperature – is assessed by means of Sobol indices. The influence of input parameters on the long-term asymptote as well as short-term transient evolution of the systems is discussed, depending on whether gravitational removal is included or not in the models.

Physicochemical Approach to Pour Point Depressant Treatment of Waxy Crudes

A physicochemical approach was taken to show wax-based and crude oil-based differences between three waxy crudes (Amenam, Norne, and Varandey), that had similar amounts of wax according to DSC crystallizable areas, that were responsible for very different responses to pour point depressant additive treatments. Varandey crude oil was the most difficult to treat, and the effectiveness of the additives decreased with time when the oil had been aged for 2 years prior to treating with the additives. Detailed compositional analysis of these three crude oils, and their waxes, showed that Varandey contains the highest concentration of longer n-paraffins, significantly more total n-paraffins, a higher wax appearance temperature, the highest amount of wax that can be centrifuged at ambient temperature, a bimodal distribution of crystallizable waxes by DSC, more saturates in the heavy ends by the Saturates, Aromatics, Resins-Asphaltene Determinator, a very high amount of Waxphaltene Determinator Waxy B (–24 °C methyl ethyl ketone precipitated waxes that do not dissolve in heptane at that temperature but melt at 60 °C in heptane) and very little asphaltenes that do not flocculate. These additional characterization methods, including the wax appearance temperature, show that the amount of wax by DSC is not discriminating for some crude oils. Microscopy of Varandey showed large fractal crystalline domains that were different from Amenam, which showed classic large macrocrystalline needle-like crystals, or Norne that had a gelled network with much smaller needle-like crystals. Norne is less responsive to additive treatment than Amenam despite having significantly less n-paraffins, Waxphaltene Determinator Waxy B waxes, and asphaltenes. Simulated distillation shows that Norne is the heaviest oil and has the highest amount of isomeric material in the C24–C34 range and a higher temperature wax appearance temperature. Furthermore, its asphaltenes flocculated with the addition of isooctane at 60 °C, whereas the asphaltenes did not flocculate in Amenam. The higher amount of isomeric material by GCMS and the much smaller needle-like crystallites suggest that Norne wax is more microcrystalline in nature. Centrifuging Varandey waxes and doping them into Amenam and Norne resulted in the doped crude oils having a bimodal DSC profile with a higher wax appearance temperature. The presence of Varandey wax caused the oils to be significantly less responsive to pour point additive treatments. Overall, for these relatively similar crude oils, it is shown that the nature of the highest carbon number waxes, the wax appearance temperature, and the amount of the least soluble waxes are significantly more important than the crude oil composition when treating with additives since they will dictate the temperature at which n-paraffins first self-associate leading to crystal nucleation.

Elastic stability criteria of seven crystal systems and their application under pressure: Taking carbon as an example

Elastic stability criteria are widely employed to prove the being of the lattice. Sin'ko and Smirnov have reported the applicable criteria under isotropic pressure and given the equations between the elastic constants C ~ i j and C i j under pressure. On this basis, the closed forms of necessary and sufficient conditions for elastic stability in all crystal classes have been presented, which are popular in normal pressure. However, the forms of elastic stability criteria under pressure are still fragmented in various literature studies. Carbon is an element with a rich variety of allotropes, and because of its excellent mechanical and electronic properties, it gains enduring and intense attention, while its phase diagram is poorly known. In order to systematically study the response of various carbon stabilities to pressure and offer some valuable insights into experimental exploration, we derive the total forms of mechanical stability criteria under isotropic pressure and calculate the mechanical stability of 46 carbon allotropes involving seven crystal systems under pressure.

Tetrahedral Frame Fields via Constrained Third-Order Symmetric Tensors

Tetrahedral frame fields have applications to certain classes of nematic liquid crystals and frustrated media. We consider the problem of constructing a tetrahedral frame field in three dimensional domains in which the boundary normal vector is included in the frame on the boundary. To do this we identify an isomorphism between a given tetrahedral frame and a symmetric, traceless third order tensor under a particular nonlinear constraint. We then define a Ginzburg-Landau-type functional which penalizes the associated nonlinear constraint. Using gradient descent, one retrieves a globally defined limiting tensor outside of a singular set. The tetrahedral frame can then be recovered from this tensor by a determinant maximization method, developed in this work. The resulting numerically generated frame fields are smooth outside of one dimensional filaments that join together at triple junctions.

Exploration of new chiral hybrid semiconducting palladium halide complexes: [(R)/(S)-2-Methylpiperazinediium]PdCl4

Chiral organic-inorganic halogenometallate hybrids have attracted significant research interest in various fields from optoelectronic to photovoltaic devices. However, to this day the range of available chiral hybrid metal halides still remains limited. In this context, single crystals of organically templated chiral chloropalladate (II), [(R)/(S)-C5H14N2]PdCl4, have been synthesized. Each of the chiral molecular compound consists of (R) or (S)-2-methylpiperazinediium [C5H14N2]2+ cations and [PdCl4]2− anions. The complexes, [(R)/(S)-C5H14N2]PdCl4 crystallize in the chiral space group P212121 (No. 19), which exhibits the enantiomorphic crystal class 222 (D2). In the crystal structure, the [PdCl4]2− anions are linked to the organic cations through NH…Cl and CH…Cl hydrogen bonds to form cation-anion-cation molecular units. The incorporation of a protonated (R) or (S)-2-methylpiperazine cations into the same inorganic halide systems leads to similar properties. The thermal analysis, optical and electric properties of [(R)-C5H14N2]PdCl4 (1) compound have been studied. The title compound [(R)-C5H14N2]PdCl4 (1) reveals thermal stability up to ca. 450 K. Besides, [(R)-C5H14N2]PdCl4 (1) shows semiconducting behavior with an optical band gap of ∼3.64 eV. The electric properties are investigated and the equivalent circuit is chosen and confirms the contribution of the grain and grain boundaries. The values of AC conductivities (10−6 Ω−1cm−1) confirm the gap energy and the semiconducting character of the R enantiomer. The value of activation energy is determinated and shows the ionic conduction type. Such a chiral hybrid metal halide offers a viable strategy for the targeted design and synthesis of non-centrosymmetric metal halide materials for optoelectronic applications.

Intrinsic Nonlinear Planar Hall Effect.

We propose an intrinsic nonlinear planar Hall effect, which is of band geometric origin, independent of scattering, and scales with the second order of electric field and first order of magnetic field. We show that this effect is less symmetry constrained compared with other nonlinear transport effects and is supported in a large class of nonmagnetic polar and chiral crystals. Its characteristic angular dependence provides an effective way to control the nonlinear output. Combined with first-principles calculations, we evaluate this effect in the Janus monolayer MoSSe and report experimentally measurable results. Our work reveals an intrinsic transport effect, which offers a new tool for material characterization and a new mechanism for nonlinear device application.

A network of hydrogen bonds in the lattice of heavy atoms of single crystals of the KDP group: quantum nature of dipole interactions

In the work presented, the distinctive features of temperature behavior of dielectric permittivity ε, dielectric loss tangent tanδ and pyroelectric coefficient γ of classical ferroelectric KDP and crystals of its family, which have a network of strong OH…O hydrogen bonds, are discussed. Particular attention is focused on the evidence of quantum-chemical interactions in network of hydrogen bonds in the matrix of heavy nuclei.

Maleic Acid as a Co-Former for Pharmaceutically Active GABA Derivatives: Mechanochemistry or Solvent Crystallization?

In this study, we compare the mechanochemical and classical solvent crystallization methods for forming maleates of GABA and its pharmaceutically active derivatives: Pregabalin, Gabapentin, Phenibut, and Baclofen. Common characterization techniques, like powder and single crystal X-ray diffraction, IR-spectroscopy, differential scanning calorimetry, thermogravimetric analysis and 1H-NMR spectroscopy, are used for the evaluation of structural and physicochemical properties. Our work shows that maleate formation is possible with all investigated target compounds. Large increases in solubility can be achieved, especially for Pregabalin, where up to twentyfold higher solubility in its maleate compared to the pure form can be reached. We furthermore compare the mechanochemical and solvent crystallization regarding quickness, reliability of phase production, and overall product quality. A synthetic route is shown to have an impact on certain properties such as melting point or solubility of the same obtained products, e.g., for Gabapentin and Pregabalin, or lead to the formation of hydrates vs. anhydrous forms. For the GABA and Baclofen maleates, the method of crystallization is not important, and similarly, good results can be obtained by either route. In contrast, Phenibut maleate cannot be obtained pure and single-phase by either method. Our work aims to elucidate promising candidates for the multicomponent crystal formation of blockbuster GABA pharmaceuticals and highlight the usefulness of mechanochemical production routes.

Direct Imaging of the Kinetic Crystallization Pathway: Simulation and Liquid-Phase Transmission Electron Microscopy Observations.

The crystallization of materials from a suspension determines the structure and function of the final product, and numerous pieces of evidence have pointed out that the classical crystallization pathway may not capture the whole picture of the crystallization pathways. However, visualizing the initial nucleation and further growth of a crystal at the nanoscale has been challenging due to the difficulties of imaging individual atoms or nanoparticles during the crystallization process in solution. Recent progress in nanoscale microscopy had tackled this problem by monitoring the dynamic structural evolution of crystallization in a liquid environment. In this review, we summarized several crystallization pathways captured by the liquid-phase transmission electron microscopy technique and compared the observations with computer simulation. Apart from the classical nucleation pathway, we highlight three nonclassical pathways that are both observed in experiments and computer simulations: formation of an amorphous cluster below the critical nucleus size, nucleation of the crystalline phase from an amorphous intermediate, and transition between multiple crystalline structures before achieving the final product. Among these pathways, we also highlight the similarities and differences between the experimental results of the crystallization of single nanocrystals from atoms and the assembly of a colloidal superlattice from a large number of colloidal nanoparticles. By comparing the experimental results with computer simulations, we point out the importance of theory and simulation in developing a mechanistic approach to facilitate the understanding of the crystallization pathway in experimental systems. We also discuss the challenges and future perspectives for investigating the crystallization pathways at the nanoscale with the development of in situ nanoscale imaging techniques and potential applications to the understanding of biomineralization and protein self-assembly.

Strain engineering a persistent spin helix with infinite spin lifetime

Persistent spin textures (PSTs) in solid-state materials arise from a unidirectional spin-orbit field in momentum space and offer a route to deliver long carrier spin lifetimes sought for future quantum microelectronic devices. Nonetheless, few three-dimensional materials are known to host PSTs owing to crystal symmetry and chemical requirements. There are even fewer examples demonstrated experimentally. Here we report that high-quality persistent spin textures can be obtained in the polar point groups containing an odd number of mirror operations. We use representation theory analysis and electronic structure calculations to formulate general discovery principles to identify PSTs hidden in known complex ternary layered and perovskite structures with large electric polarizations. We then show some of these materials exhibit PSTs without requiring any special crystalline symmetries. This finding removes the limitation imposed by mirror-symmetry protected PSTs that has limited compound discovery. Our general design approach enables the pursuit of persistent spin helices in materials exhibiting the $C_{3v}$ crystal class adopted by many quantum materials exhibiting large Rashba coefficients.

SYNTHESIS OF POTENTIAL LIQUID CRYSTALS WITH CHOLESTEROL FRAGMENT BY WITTIG REACTION

Liquid crystals are substances that owing to the features of their structure and physical properties are of interest not only as objects for theoretical research, but also significantly important practically due to the possibilities of their effective application in various brunches of industry, medicine, in household etc. Among the known classes of liquid crystals, substances known as cholesterics are an important group.
 Cholesteric liquid crystals demonstrate very high optical activity, that significantly exceeds the optical activity of most other known classes of organic compounds. Their ability for appreciable change of color at change of the temperature and environment composition is also practically important.
 Among all compounds belonging to the class of cholesterics an important place possess cholesterol derivatives, especially cholesterol esters. Therefore, the elaboration of new methods of their synthesis and the introduction of new functional groups into their molecules are an urgent tasks indeed.
 This work is devoted to the investigation of the possibility of synthesis of new cholesterol derivatives, namely cholesteryl esters of unsaturated acids by the Wittig reaction - the interaction of various classes of aldehydes with phosphonium salts, with the intermediate formation of phosphorus ylides - alkylidene phosphoranes. We found that the Wittig reaction is a convenient method for the synthesis of cholesteryl esters of unsaturated carboxylic acids. We have developed methods for the synthesis of potential cholesteric liquid crystals by the Wittig reaction, which use a phosphonium salt containing a cholesterol fragment and corresponding aldehydes. The process proceed without the release of an intermediate compound – alkylidene phosphorane, which reduces the labor intensity of the method.
 The application of various aldehydes enables the easily obtaining of cholesteryl esters of unsaturated acids containing various aliphatic, aromatic and heterocyclic fragments in the acid radical. The reaction takes place in mild conditions, without using of high temperatures or aggressive environments. The resulting esters show signs of mesophase formation, which is a confirmation of their liquid crystalline properties.

Dissipative time crystals originating from parity-time symmetry

The authors provide evidence for the emergence of a class of dissipative time crystals when parity-time ($\mathcal{P}\phantom{\rule{0}{0ex}}\mathcal{T}$) symmetry is restored in collective spin systems with Lindblad dynamics. They show that a standard model of boundary time crystals satisfies Liouvillian $\mathcal{P}\phantom{\rule{0}{0ex}}\mathcal{T}$ symmetry, and prove that boundary time crystals exist only when the stationary state is $\mathcal{P}\phantom{\rule{0}{0ex}}\mathcal{T}$ symmetric in the large-spin limit.

Slow melting of a disordered quantum crystal

The melting of the corner of a crystal is a classical, real-world, non-equilibrium statistical mechanics problem which has shown several connections with other branches of physics and mathematics. For a perfect, classical crystal in two and three dimensions the solution is known: the crystal melts reaching a certain asymptotic shape, which keeps expanding ballistically. In this paper, we move onto the quantum realm and show that the presence of quenched disorder slows down severely the melting process. Nevertheless, we show that there is no many-body localization transition, which could impede the crystal to be completely eroded. We prove such claim both by a perturbative argument, using the forward approximation, and via numerical simulations. At the same time we show how, despite the lack of localization, the erosion dynamics is slowed from ballistic to logarithmic, therefore pushing the complete melting of the crystal to extremely long timescales.

Effects of Biliary Phospholipids on Cholesterol Crystallization and Growth in Gallstone Formation.

The prevalence of cholesterol gallstone disease is increasing, primarily due to the global epidemic of obesity associated with insulin resistance, and this trend leads to a considerable healthcare, financial, and social burden worldwide. Although phospholipids play an essential role in maintaining cholesterol solubility in bile through both mixed micelles and vesicles, little attention has been paid to the impact of biliary phospholipids on the pathogenesis of cholesterol gallstone formation. A reduction or deficiency of biliary phospholipids results in a distinctly abnormal metastable physical-chemical state of bile predisposing to supersaturation with cholesterol. Changes in biliary phospholipid concentrations influence cholesterol crystallization by yielding both liquid crystalline and "anhydrous" crystalline metastable intermediates, evolving into classical parallelogram-shaped cholesterol monohydrate crystals in supersaturated bile. As a result, five distinct crystallization pathways, A-E, have been defined, mainly based on the prime habits of liquid and solid crystals in the physiological or pathophysiological cholesterol saturation of gallbladder and hepatic bile. This review concisely summarizes the chemical structures and physical-chemical properties of biliary phospholipids and their physiological functions in bile formation and cholesterol solubility in bile, as well as comprehensively discusses the latest advances in the role of biliary phospholipids in cholesterol crystallization and growth in gallstone formation, largely based on the findings from clinical and animal studies and in vitro experiments. The insights gleaned from uncovering the cholelithogenic mechanisms are expected to form a fundamental framework for investigating the hitherto elusive events in the earliest stage of cholesterol nucleation and crystallization. This may help to identify better measures for early diagnosis and prevention in susceptible subjects and effective treatment of patients with gallstones.

Supramolecular reinforcement drastically enhances thermal conductivity of interpenetrated covalent organic frameworks

Interpenetration of covalent organic frameworks can lead to drastic enhancements in their thermal conductivities, thus marking a novel regime of materials design combining high porosities with mechanical flexibilities and high thermal conductivities.

A new dual-ligand DUT-52-type metal-organic framework for ratiometric luminescence detection of aqueous-phase Cu2+ and Cr2O72.

Metal-organic frameworks (MOFs) are a unique class of multifunctional hybrid crystals that have been successfully utilized in diverse ranges of applications. However, since MOFs are prone to aqueous degradation, the development of stable luminescent MOF platforms in aqueous media is still a huge challenge. Here, a novel dual-ligand Eu3+/DUT-52-COOH composite is prepared based on the luminescent DUT-52 prototype structure via a dual-ligand strategy and a post-synthetic modification (PSM) method. The functionalized Eu3+/DUT-52-COOH material exhibits dual emission and good photothermal stability in aqueous media. Thus, Eu3+/DUT-52-COOH is developed as a ratiometric luminescent sensor to achieve highly selective and sensitive detection of Cu2+ and Cr2O72- in aqueous solutions and has a low detection limit of 3.43 μM and 25.7 nM, respectively. This work is one of the few cases of detecting Cu2+ and Cr2O72- in aqueous media based on a DUT-52, and the detection signals can be observed by the bare eye without using sophisticated analytical instruments. The possible sensing mechanism is discussed in detail. The results obtained in this project may provide broad prospects for developing smart sensing systems to accomplish highly efficient, easily operable and quantitative intelligent recognition of Cu2+ and Cr2O72-.

ON TWINNING-MEDIATED VOID GROWTH IN HEXAGONAL CRYSTALS

Aspects of plastic anisotropy in damage accumulation are considered for a class of hexagonal crystals that deform by combined slip and twinning. Focus is placed on crystallographic aspects that are currently absent from constitutive formulations of ductile damage. To this end, three-dimensional finite-element calculations are carried out using a cubic unit cell containing a single void embedded in a crystal matrix. Plastic flow in the latter is described using crystal plasticity with parameters representative of single crystal pure magnesium. The effect of void oblateness is analyzed in some detail, as voids often form as blunted microcracks in Mg alloys. The analyses reveal two aspects peculiar to twinning-mediated void growth: (1) insensitivity of the effective stress-strain response to void oblateless and (2) a plastic auxetic effect. Both aspects manifest under certain circumstances. Some implications in terms of incorporating the uncovered crystallographic aspects in coupled plasticity-damage formulations of anisotropic materials are discussed.