Homogeneous Crystals Research Articles

Evaluation of Versatile CdS Nanomaterials Based Liquid Crystals Switchable Device.

Novel synthesis and properties of versatile CdS nanostructures (e.g., Nano-brush, nano-cube, nanosphere) dispersed liquid crystals application in chemical friendly medium exploring this article. Most recent studies, CdS nano-wire brush with the stacking fault structures were hydrothermally synthesized through a dissolution-recrystallization approach in concentrated ammonia solvent in one step solution, for the first time. Those structures-property relations with respect to ferroelectric hydrogen-bonded liquid-crystalline complex (HBLC; AC + 5BAO) controlled and efficient formation of surface relief nanostructures. A successful attempt has been made to form hydrogen bonding between CdS nanostructures and supramolecular LC with p–n-alkyloxy benzoic acids (n-OBA). The formation of an inter-H-bond is evinced through FTIR study, as well as Gaussian simulation also ensures complete formation of intermolecular hydrogen bond optimized geometry. In contrast, a new sensitive response of smectic G ordering observed in this series is investigated by constructing a phase diagram obtained from two binary mixtures of CdS nanostructures influenced by homogeneous liquid crystals. Temperature-dependent dielectric relaxation, tilt angle, electro-optical switching measurements allow for monitoring very unique and useful behavior in that the polarization of the emission from the semiconductor nanostructures can be controlled by an external bias. It reveals electrically tunable interaction of the composites may allow for engineering of practical electro-optic switchable device.

Effect of γ precipitates on thermal and acoustic noises emitted during austenite/martensite transformation in NiFeGaCo single crystals

It is shown that the presence of particles of the γ-phase in NiFeGaCo single crystals has an influence on the mode of the formation of the martensite phase: while in the homogeneous (free of precipitates) sample the transformation underwent by single interface motion, in samples with precipitates many martensite needles were formed and grown in two specific directions. Similarly the shape and the area of hysteresis curves are also different. These differences are accompanied with differences in the critical exponents of distributions of the energy (determined from both thermal and acoustic noises) and the amplitude (obtained from acoustic emission measurements). In addition the values of these exponents were different for heating and cooling. We found a definite correlation between the relative changes of these exponents and the ratios of the numbers of hits and integrated energies of acoustic emission during heating and cooling: if the later ratios were negative then the changes in the exponents had opposite sign, if the exponent was larger for heating than cooling, then the energy of acoustic emission was smaller for heating than cooling. In homogeneous crystals without γ-phase precipitates positive asymmetry was obtained while in crystals with large γ-phase precipitates (5–15 μm) negative asymmetry was observed. Aged crystals with bimodal structure (large and small γ-phase particles 5–15 μm + 150–300 nm) are between these cases: the relative changes are practically zero.

Control of morphology and lamellae orientations in thin poly (ε-caprolactone) films by blending with different molar mass of polystyrene

The morphology and lamellar orientations in the thin blend films (∼30nm) of poly(ε-caprolactone) (PCL) and different molar mass of polystyrene(PS) were investigated by atomic force microscopy (AFM). The influence of PS molar mass on the PCL crystal structures was studied. The results show that both fibrous edge-on and flat-on microcrystal can be obtained when low molar mass PS (LPS with Mw=3.7k and 7.5k) is added into the thin PCL films, while only flat-on crystal is constructed for the films blending with high molar mass PS (HPS with Mw=15.5k and 54k and 106k). The different crystal morphology formation is explained based on the competition between phase separation and crystallization. For the LPS/PCL blend films, it is the homogeneous nucleation crystallization of PCL at the films surface that leads to the formation of fibrous edge-on together with several isolated and faceted flat-on crystals. While for the HPS/PCL blend films, it is the first vertical phase separation followed by the heterogeneous nucleation of PCL at polymer/substrate interface process that results in the morphology of flat-on PCL crystal decorated by PS domain island or dewetting hollows on the top.

Phase Matching Using the Linear Electro-Optic Effect

Phase matching is a necessary condition for achieving high-efficiency optical-frequency conversion. To date, practical means of accomplishing phase matching in homogeneous crystals remain limited, despite considerable efforts. Herein, we report a new class of methods aimed at achieving quasiperfect phase matching, based on controllable birefringence produced via the linear electro-optic effect, termed "voltage-tuning phase matching." The wave vectors of the induced polarization and the generated fields can be matched and maintained along the direction of propagation by introducing an external electric field. We analyze the validity and feasibility of this method theoretically and demonstrate it experimentally by applying the linear electro-optic effect and fourth-harmonic generation simultaneously in a partially deuterated KH_{2}PO_{4} crystal. Quasiperfect phase matching is achieved systematically over a temperature range of the initial phase-matching temperature ±2 °C. Moreover, this method can overcome the limitation of the birefringence in traditional technologies and provides new functionalities for conventional nonlinear materials as well as low-birefringence and isotropic materials. This technology may significantly impact the study of optical-frequency conversion and has promise for a broad range of applications in nonlinear optics.

Examining the role of fluctuations in the early stages of homogenous polymer crystallization with simulation and statistical learning.

We propose a relationship between the dynamics in the amorphous and crystalline domains during polymer crystallization: the fluctuations of ordering-rate about a material-specific value in the amorphous phase drive those fluctuations associated with the increase in percent crystallinity. This suggests a differential equation that satisfies the three experimentally observed time regimes for the rate of crystal growth. To test this postulated expression, we applied a suite of statistical learning tools to molecular dynamics simulations to extract the relevant phenomenology. This study shows that the proposed relationship holds in the early time regime. It illustrates the effectiveness of soft computing tools in the analysis of coarse-grained simulations in which patterns exist, but may not easily yield to strict quantitative evaluation. This ability assists us in characterizing the critical early time molecular arrangement during the primary nucleation phase of polymer melt crystallization. In addition to supporting the validity of the proposed kinetics expression, the simulations show that (i) the classical nucleation and growth mechanism is active in the early stages of ordering; (ii) the number of nuclei and their masses grow linearly during this early time regime; and (iii) a fixed inter-nuclei distance is established.

Regularity and Locality of Point Defects in Multilattices

We formulate a model for a point defect embedded in a homogeneous multilattice crystal with an empirical interatomic potential interaction. Under a natural phonon stability assumption, we quantify the decay of the long-range elastic fields with increasing distance from the defect. These decay estimates are an essential ingredient in quantifying approximation errors in coarse-grained models and in the construction of optimal numerical methods for approximating crystalline defects.

Apatite Glass-Ceramics: A Review

This article is a review of the published literature on apatite glass-ceramics (GCs). Topics covered include crystallization mechanisms of the various families of the apatite GCs and an update on research and development on apatite GCs for applications in orthopedics, dentistry, optoelectronics and nuclear waste management. Most apatite GCs crystallize through a homogenous nucleation and crystallization mechanism, which is aided by a prior liquid-liquid phase separation. Careful control of the base glass composition and heat-treatment conditions, which determine the nature and morphology of the crystal phases in the GC can produce GC materials with exceptional thermal, mechanical, optical and biological properties. The GCs reviewed for orthopedic applications exhibit suitable mechanical properties and can chemically bond to bone and stimulate its regeneration. The most commercially successful apatite GCs are those developed for dental veneering. These materials exhibit excellent translucency and clinical esthetics, and mimic the natural tooth mineral. Due to the ease of solid solution of the apatite lattice, rare earth doped apatite GCs are discussed for potential applications in optoelectronics and nuclear waste management. One of the drawbacks of the commercial apatite GCs used in orthopedics is the lack of resorbability, therefore the review provides a direction for future research in the field.

The structure and optical properties of Lithium Niobate grown on quartz for photonics application

This paper focuses on the structure and optical properties of Lithium niobate (LN) deposited on quartz substrate by sol-gel method. The solution was prepared at different molarity concentration and annealed at 500 °C. The LNs were analyzed by UV-visible, X-ray diffraction (XRD) and Scanning Electron Microscope (SEM). The results show that as the molar concentration increases, the films crystallization becomes more atomically distributed and the energy band gap approaches 4 eV. Transmission spectra were taken in the wavelength range of 400-1100 nm. Hexagonal structure was observed with good atoms distribution and homogeneous crystallization. There were two phases of LNs recorded in this work.

Ralstonite Renamed Hydrokenoralstonite, Coulsellite Renamed Fluornatrocoulsellite, and Their Incorporation Into the Pyrochlore Supergroup

Abstract Ralstonite is renamed hydrokenoralstonite, ideally □ 2 Al 2 F 6 (H 2 O). “Atroarite” and the “AHF” phase (hydrated aluminum hydroxy-fluoride, a “ralstonite-like mineral”) are also hydrokenoralstonite. The name ralstonite is transferred to the group, where M 3+ cations are dominant at the B site, and Al is dominant among them, and F 1– is the dominant anion at the X site. Hydrokenoralstonite from the Pitinga mine, Presidente Figueiredo, Amazonas, Brazil, is intimately associated with galena and sphalerite. It forms chemically homogeneous octahedral crystals, from 0.1 to 1 mm in size. The mineral is colorless with white streak, vitreous luster, transparent, density (calc.): 2.554 g/cm 3 . Its empirical formula is (□ 1.87 Na 0.12 Rb 0.01 ) Σ2.00 (Al 1.86 Mg 0.14 ) Σ2.00 [F 3.46 (OH) 2.54 ] Σ6.00 (H 2 O). The mineral is cubic, (#227), a 9.8455(7) A, V 954.36 (12) A 3 , Z = 8. Hydrokenoralstonite exhibits (Al,Mg) cations with octahedral coordination and Na cations located within distorted cubes. Coulsellite, a rhombohedral pyrochlore-supergroup mineral, ideally (Na,Ca) 2 (Mg,Al) 2 F 6 F, is renamed fluornatrocoulsellite, and the name coulsellite is transferred to the group, where M 2+ cations are dominant at the B site, and Mg is dominant among them, and F 1– is the dominant anion at the X site. This nomenclature proposal was approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association.

Influence of the yttria dopant on the structure and properties of (ZrO2)0.91–x (Sc2O3)0.09(Y2O3) х (x = 0–0.02) crystals

We have studied the influence of the yttrium oxide (Y2O3) dopant (1 and 2 mol %) on the phase composition, structure, and electrical properties of ZrO2–9 mol % Sc2O3 solid solution. Stabilization of ZrO2 jointly with 9 mol % Sc2O3 and 2 mol % Y2O3 is shown to allow the acquisition of high phase stability transparent homogeneous crystals with a cubic structure. Their mechanical grinding is established to cause no change in the phase composition of these crystals, whereas the powders retain the initial fluorine structure. The powders preserved the original structure of the fluorite crystals. All the probed crystals reveal high microhardness and low fracture toughness. Increasing the Y2O3 concentration in the crystals led to a reduction of the maximum loads on the indenter, which the sample withstood without cracking. As is shown, the specific conductivity exhibits nonmonotonic behavior depending on the Y2O3 concentration in the crystals. Increasing the Y2O3 content to 2 mol % in the solid electrolyte reduces the conductivity of the crystals in the entire temperature range that is attributed to a decrease in the carrier mobility due to the increasing ion radius of the stabilizing ion.

Electrospray deposition device used to precisely control the matrix crystal to improve the performance of MALDI MSI.

MALDI MSI has been recently applied as an innovative tool for detection of molecular distribution within a specific tissue. MALDI MSI requires deposition of an organic compound, known as matrix, on the tissue of interest to assist analyte desorption and ionization, in which the matrix crystal homogeneity and size greatly influence the imaging reproducibility and spatial resolution in MALDI MSI. In this work, a homemade electrospray deposition device was developed for deposition of matrix in MALDI MSI. The device could be used to achieve 1 μm homogeneous matrix crystals in MALDI MSI analysis. Moreover, it was found, for the first time, that the electrospray deposition device could be used to precisely control the matrix crystal size, and the imaging spatial resolution was increased greatly as the matrix crystals size becoming smaller. In addition, the easily-built electrospray deposition device was durable for acid, base or organic solvent, and even could be used for deposition of nanoparticles matrix, which made it unparalleled for MALDI MSI analysis. The feasibility of the electrospray deposition device was investigated by combination with MALDI FTICR MSI to analyze the distributions of lipids in mouse brain and liver cancer tissue section.

Nano-volcanic Eruption of Silver.

Silver (Ag) is one of the seven metals of antiquity and an important engineering material in the electronic, medical, and chemical industries because of its unique noble and catalytic properties. Ag thin films are extensively used in modern electronics primarily because of their oxidation-resistance. Here we report a novel phenomenon of Ag nano-volcanic eruption that is caused by interactions between Ag and oxygen (O). It involves grain boundary liquation, the ejection of transient Ag-O fluids through grain boundaries, and the decomposition of Ag-O fluids into O2 gas and suspended Ag and Ag2O clusters. Subsequent coating with re-deposited Ag-O and the de-alloying of O yield a conformal amorphous Ag coating. Patterned Ag hillock arrays and direct Ag-to-Ag bonding can be formed by the homogenous crystallization of amorphous coatings. The Ag “nano-volcanic eruption” mechanism is elaborated, shedding light on a new mechanism of hillock formation and new applications of amorphous Ag coatings.

Liquid Crystal Alignment on Ion-beam Irradiated Hafnium Strontium Oxide Films

Homogeneous liquid crystal (LC) alignment on hafnium strontium oxide (HfSrO) films prepared by sol-gel process via ion-beam (IB) bombardment was investigated. Uniform LC alignment was achieved on the IB-irradiated HfSrO films at IB intensity of 1.8 keV. We confirmed the effect of surface morphology on LC alignment using field-emission scanning electron microscope (FE-SEM). In addition, we observed electro-optical characteristics of the twisted-nematic (TN)-LC cells based on HfSrO films to verify the possibility of LC display (LCD) application.

Macroinhomogeneity of the properties of semiconductor crystals due to the specifics of the melt’s behavior under microgravity conditions

The effect of convective flows caused by the changing direction of the residual gravitational vector relative to the solidification front on the radial inhomogeneity (macrosegregation) of the dopant distribution in semiconductor crystals is studied within the context of mathematical and physical simulation for terrestrial and space conditions. Theoretical calculations and experimental research are carried out by the example of the growth of Ge crystals and their heavy doping with Ga (1019 сm–3). The velocities of convective flows near the solidification front which lead to radial macroinhomogeneity in the grown crystals are theoretically calculated. The requirements to obtain homogeneous semiconductor crystals under real microgravity conditions are formulated.

The TTT Curves of the Heterogeneous and Homogeneous Crystallization of Lithium Disilicate – A Stochastic Approach to Crystal Nucleation

The present study explores the temperature and time dependence of heterogeneous crystal nucleation in a lithium disilicate glass using the stochastic approach. In particular a single lithium disilicate sample was repeatedly (284 runs) undercooled to 1173 K in a PtRh-crucible and the crystallization onset time during an isothermal hold was detected in each run. The statistical distribution of the times elapsed before crystallization is described by a first order reaction with a heterogeneous crystal nucleation rate of (9.19 ± 0.04) × 10-4 s-1 while individually shaped crystallization exotherms of each run were recorded which indicate growth of a single or only few crystals during crystallization of the entire volume. The data were used together with results of previous stochastic experiments and those of double-stage heat treatments to calculate the crystallization time of a fraction of 10-4 percent for all temperatures between glass transition and melting. The derived TTT diagram shows a double nose of crystallization in the volume at large undercoolings (0.53–0.61 Tm) and crystallization at the surface at small undercoolings (0.62–0.92 Tm) initiated by homogeneous and heterogeneous crystal nucleation, respectively. The critical cooling rate at the heterogeneous nose is approximately 73 K s-1.

Control of organic polymorph formation: crystallization pathways in acoustically levitated droplets

Abstract Theoretical and experimental studies indicate that crystal nucleation can take more complex pathways than expected on the ground of the classical nucleation theory. Among these pathways are the formation of pre-nucleation clusters and amorphous precursor phases. A direct in situ observation of the different pathways of nucleation from solution is challenging since the paths can be influenced by heterogeneous nucleation sites, such as container walls. Here, we provide insights into the crystallization process using the in situ combination of an acoustic levitator, Raman spectroscopy, and X-ray scattering. The contactless sample holder enables the observation of homogeneous crystallization processes and the detection of intermediates and final crystalline forms. We provide evidence for the existence of multiple pathways of nucleation based on the investigation of the crystallization of organic molecules from different solvents. Starting from a diluted solution, a supersaturation is reached during the experiment due to the evaporation of the solvent. The highly supersaturated solution reveals different pathways of crystallization. Depending on the degree of supersaturation either the thermodynamically stable or the metastable crystal form is observed.

Method for calculating the sizes of nucleation centers upon homogeneous crystallization from a supercooled liquid

An alternative approach to calculating critical sizes lk of nucleation centers and work Ak of their formation upon crystallization from a supercooled melt by analyzing the variation in the Gibbs energy during the phase transformation is considered. Unlike the classical variant, it is proposed that the transformation entropy be associated not with melting temperature TL but with temperature T < TL at which the nucleation of crystals occurs. New equations for lk and Ak are derived. Based on the results from calculating these quantities for a series of compounds, it is shown that this approach is unbiased and it is possible to eliminate known conflicts in analyzing these parameters in the classical interpretation.

Solidification ofHe4clusters adsorbed on graphene

We determined the ground state of $^{4}\mathrm{He}_{N}$ clusters adsorbed on one side of graphene for selected cluster sizes in the range from $N=20$ to $N=127$. For all investigated clusters variational and diffusion Monte Carlo simulations were performed at $T=0$ K, and in addition for a selected subset finite temperature path integral Monte Carlo. At $T=0$ K the liquid or solid character of each cluster was investigated by restricting the phase using corresponding importance sampling trial-wave functions. The $^{4}\mathrm{He}$-graphene interaction was modeled as a sum of individual $^{4}\mathrm{He}$-C interactions, where both isotropic and anisotropic models were tested; also the effect of the substrate-mediated McLachlan interaction was investigated. We have found homogeneous crystallization in models of anisotropic interactions, starting from clusters with $N=26$ atoms in simulations without the McLachlan interaction, and between $N=37$ and 61 when it is included. The atoms become increasingly delocalized as one moves from the center of the cluster to the perimeter, evidenced by the Lindemann parameter. On the other hand, in the case of the isotropic interaction model, a liquidlike structure is more favorable for all considered cluster sizes. We use a liquid-drop model to extrapolate the energy per particle to the $N\ensuremath{\rightarrow}\ensuremath{\infty}$ limit, and the results are compared with the values obtained in studies of bulk $^{4}\mathrm{He}$ on graphene. Low-temperature path integral Monte Carlo simulations are in agreement with ground-state results.

Removal of heavy metal ions from water by an combined sorption–crystallization process using activated clays

The degree of comminution of materials in an ultrasonic field has been theoretically estimated by calculating the maximum and minimum energy inputs necessary for this process (upper and lower estimates have been obtained). The degree of comminution of kaolin in an ultrasonic bath determined by light and electron microscopy is in satisfactory agreement with the theoretical estimates. The efficiencies of heavy metal ion (Cu2+, Ni2+) removal from aqueous solutions in the following processes have been compared: adsorption on natural materials (kaolin and bentonite), chemical precipitation in homogeneous crystallization, and integrated sorption–crystallization process using activated clays. The highest purification efficiency has been attained in the integrated process preceded by ultrasonication of the clay slurry and alkaline reagent. Use of these sonochemically activated additives has shortened the duration of the integrated process and has increased the degree of removal of toxic metals to 102–103. Clays have been demonstrated to act as a sorbent, a heterogeneous crystallization stimulator, and a coagulant accelerating the sedimentation of the solid phase.

Temperature Dependence of Morphology of Transcrystalline at the Interface of Carbon Fiber and Poly (L‐Lactic Acid) Composite Under a Temperature Gradient Stage

SummaryThin film of carbon fiber (CF) and poly (L‐lactic acid) (PLLA) composite was prepared by a solution casting technique. Influence of crystallization temperature (Tc) on morphology of transcrystalline (TC) on the interface between CF and PLLA was investigated under a temperature‐controlled gradient (T‐gradient) stage with temperature ranging from 90 °C to 140 °C. Morphology of TC was observed by polarized optical microscope (POM). Typical TC structure isothermally crystallized on the T‐gradient stage was obtained at the surface of CF when Tc = 111 ∼ 132 °C. As Tc decreased from 132 to 111 °C, nuclei density on the surface of single fiber increased while the thickness of TC layer decreased. Crystallization kinetics of TC was investigated through isothermal crystalization under POM equipped with a temperature‐controlled stage. As Tc decreased, the nucleation rate of TC increased and the growth rate of TC decreased. Furthermore, it revealed that the thickness of TC layer was conducted by the competition between heterogeneous nucleation on the surface of fiber and homogeneous nucleation in the bulk matrix around the fiber. The nucleation rate of TC structure was much higher than homogeneous nucleation rate of spherulites in the bulk matrix when Tc was above 118 °C. In this case, TC had enough space to develop perpendicular to fiber axis. Consequently, thickness of TC layer was larger at higher crystallization temperature. On the contrary, transcrystallization was suppressed by homogeneous crystallization when Tc was below 118 °C due to enhanced nucleation ability of spherulites.