Influence of view angle of radiation and heat of fusion on the GaAs bridgman crystal growth

The paper is concerned with the numerical simulation of temperature distributions within the ingot. The effective field of view of heat exchange by radiation depending on the difference in the radii of the ingot and furnace wall flats the axial temperature gradient in the ingot and influences the position of the solid-liquid interface. In the vicinity of this interface the heat of fusion flats and increases the temperature gradient in the liquid and the solid respectively. Thereby the curvature of isotherms is changed, too.     

Growth and characterization of l-prolinium picrate single crystal: A promising NLO crystal

l-Prolinium picrate was synthesized and its solubility in the mixed solvent of acetone and water was estimated. Employing temperature reduction method crystals of size 22×4×3 mm³ were grown. The cell dimensions were obtained by single-crystal X-ray diffraction study. FT-IR, UV–vis–NIR and fluorescence spectral analyses were carried out for the grown crystals. The optical band gap estimated for this crystal is about 2.4 eV. Thermogravimetric study was carried out to determine the thermal properties of the grown crystal. Kurtz powder second harmonic generation (SHG) efficiency measurement revealed that the SHG efficiency is about 52 times that of potassium dihydrogen orthophosphate. Mechanical strength was tested by Vicker's microhardness test.     

The crystal structure of vyuntspakhite: A redetermination

The crystal structure of the mineral vyuntspakhite (Y, TR)₆{Al₂(OH)₃[H_1.48Si_1.88O₇][SiO₄][SiO₃(OH)]}₂(a = 5.7551(11) Å, b = 14.752(3) Å, c = 15.906(4) Å, β = 96.046(4)°, sp. gr. P2₁/n, Z = 2), which had been established earlier in the pseudo-unit cell, is redetermined by X-ray diffraction (R = 0.040, T = 100 K). The redetermination of the structure shows that pronounced pseudotranslation along the axis c′ = c/3 is associated with the fact that Y(TR) atoms are related by a 1/3 translation along the [001] direction. Most of the hydrogen atoms are located. The crystal-chemical function of hydrogen bonds is analyzed. In the unit cell of vyuntspakhite, the cationic layers consisting of edge-sharing (Y,TR) eight-vertex polyhedra alternate along the b axis with mixed anionic layers composed of isolated Si tetrahedra (orthotetrahedra), Si₂O₇ double-tetrahedra (diortho) groups, Al five-vertex polyhedra, and Al₂O₈ double-tetrahedra groups linked by shared vertices and through hydrogen bonding.     

Liquid Crystals: A Bibliography for 1977

X-ray diffraction, Raman spectroscopy, and x-ray photoemission measurements indicate that the metallic conductivity of iodine-doped polyacetylene results from the intercalation of iodine between close-packed planes of the parent phase to form a charge transfer complex. The polyacetylene chains donate charge to produce I₃ and a second iodine species with lower charge density, most likely I₅. The structure of this charge transfer complex can be viewed as a perturbation of the structure of the parent polymer, which has been derived from x-ray diffraction analysis and lattice energy calculations.     

Liquid Crystals: A Bibliography for 1975

Abstract

The static dielectric constants of biphenyl-4-p-n-alkoxybenzoates have been measured as functions of temperature. The dielectric anisotropy (δ?) for the successive homologues (hexyl to undecyl) shows an alternation similar to that exhibited by the nematic-isotropic transition temperature (T _NI). The dispersion of ?_∥ in the frequency range of 0.1-15 MHz has been studied for four successive members of biphenyl-4-p-n-alkoxybenzoates (heptyl to decyl derivatives) as well as of trans-p-n-alkoxy-α-methyl-p'-cyanophenyl cinnamates (eighth to eleventh members). For both series the relaxation frequency (f _R) and the frequency of dielectric isotropy (f _o) evaluated at a common relative temperature show an alternation similar to T _NI. For any given compound the Arrhenius plots for f _R and f _o give the same value of the activation energy (W). In the case of the biphenyl esters the vaue of W is the same for the seventh and eighth members, but increases for the higher members which exhibit a smectic phase at lower temperatures. On the contrary for cinnamic acid esters W is found to be the same for all homologues irrespective of whether the nematic phase is preceded by a smectic phase or not.     

Algorithmic crystal chemistry: A cellular automata approach

Atomic-molecular mechanisms of crystal growth can be modeled based on crystallochemical information using cellular automata (a particular case of finite deterministic automata). In particular, the formation of heteropolyhedral layered complexes in uranyl selenates can be modeled applying a one-dimensional three-colored cellular automaton. The use of the theory of calculations (in particular, the theory of automata) in crystallography allows one to interpret crystal growth as a computational process (the realization of an algorithm or program with a finite number of steps).     

Liquid Crystal Channel Waveguides: A Monte Carlo Investigation of the Ordering

We present detailed Monte Carlo (MC) simulations of a nematic cell with homeotropic boundary conditions at the four confining surfaces. The simulations are based on the Lebwohl-Lasher lattice spin model with boundary conditions chosen to mimic the cell anchoring. We have investigated the model using a standard Metropolis Monte Carlo method to study the optical transmission and the ordering through the cell.     

Liquid crystal material with gold nanoparticles as optical sensors active medium for the amino acids detection

Abstract

In the article, the possibility of using the cholesteric liquid crystal mixture doped by the gold nanoparticles as an active medium of optical amino acid sensors is shown. The BLO-62 and the 5CB were used as a cholesteric liquid crystal and a nematic liquid crystal correspondingly. This mixture was doped by the gold nanoparticles. The method of gold nanoparticles synthesis is considered and their parameters are determined. Studies on the spectral characteristics of the investigated materials have shown that the addition of gold nanoparticles to the system leads to a significant decreasing in the spectral characteristic steepness and give the possibility of expanding the measurement range of amino acid concentration.     

Piezoelectric effect in ferroelectric liquid crystal: A review

The data in the literature and our results of studying the piezoelectric effect in ferroelectric liquid crystals are analyzed. The existing theories of this effect in liquid crystals are discussed. The parametric transformations of electromechanical oscillations in ferroelectric liquid crystals are considered.     

A Redetermination of the crystal structure of 2-aminophenol

The crystal structure of 2-aminophenol has been redetermined from automatic diffractometer data in order to locate the hydroxyl and amino hydrogens and confirm the nature of the intermolecular hydrogen bonding. Crystals are orthorhombic, space groupPbca, witha =19.751(6),b = 7.250(3), andc = 7.852(5) Å, and eight molecules per cell. The structure was solved by Multan and refined to a conventionalR value of 0.030. The molecular geometry compares well with previously reported structures of related species. The molecules are hydrogen bonded from OH to N to form chains parallel to theb axis, with these chains linked together to form sheets by NH to O hydrogen bonds essentially parallel toc. The NH - O hydrogen bonds are 0.33 Å longer than the OH - N ones, and an explanation for this is provided which incorporates newly computed values for atomic electronegativities. Pairs of molecules are mutually hydrogen bonded across inversion centers. There are large cavities between the sheets which could conceivably result in easy intercalation of small foreign molecules, much as in the clathrates formed by urea and -quinol.     

Liquid crystal properties of dimers having two identical terminal units and a central oxyethylene spacers

ABSTRACT

In this research, we designed and synthesized blue emitting materials based on aminofluorene-substituted pyrene derivatives. Organic light-emitting diodes (OLEDs) devices using these materials were fabricated in the following sequence; ITO/N,N′-diphenyl-N,N′-(2-napthyl)-(1,1′-phenyl)-4,4′-diamine (NPB) (500 Å)/Blue emitters 1 or 2 (300 Å)/4,7-diphenyl-1,10-phenanthroline (BPhen) (300 Å)/lithium quinolate (Liq) (20 Å)/Al (1000 Å). These devices showed efficient blue emissions. Particularly, a device A using 7-(1-(2-(diphenylamino)-9,9-diethyl-9H-fluoren-7-yl)pyren-6-yl)-9,9-diethyl-N,N-diphenyl-9H-fluoren-2-amine (1) as blue emitter exhibited luminous efficiency, power efficiency, and external quantum efficiency of 2.20 cd/A, 0.80 lm/W, 1.62% at 100 mA/cm², respectively, with Commission Internationale d’Énclairage (CIE) coordinates of (0.17, 0.24) at 8.0 V.     

A more clear insight of the lysozyme crystal composition

Crystallization can be used as a purification method for proteins. Lysozyme was chosen as a model substance. Changing crystallization conditions will lead as shown to different lysozyme crystal morphologies with different properties. Beside others, lysozyme crystals can show a Tetragonal, High Temperature and Low Temperature Orthorhombic crystal morphology. Experiments such as conductivity measurements, pH tests, chloride detection tests, experiments using methylene blue as a dye and dissolution experiments were carried out to investigate the composition of the lysozyme crystals. It is proven that lysozyme crystals are made up of the initial buffer solution components: lysozyme (the protein), water which is part of the crystal lattice, salt ions which are attached to the protein molecule and voids filled with the buffer solution containing the crystallization agent (e.g. salt). Interesting dissolution behaviours of the lysozyme crystals were observed which are not described so far elsewhere (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A crowdion mechanism of crystal twinning

The processes of plastic deformation of crystals via mechanical twinning are considered. Models of nucleation and motion of twin boundaries leading to formation of twin interlayers are proposed. These models are based on the crowdion mechanism of deformation in crystals and are considered by an example of close-packed structures. Good agreement between the predictions of the models proposed and the experimental results for crystals deformed by a concentrated load is demonstrated.     

Studies on the crystal growth,crystal structure,optical and thermal properties of an organic crystal: Benzophenone hydrazone

Single crystals of benzophenone hydrazone (BH) were successfully grown by slow evaporation method at constant temperature, 30 °C. The crystal structure of BH has been determined, and it belongs to the noncentrosymmetric space group P2₁. The grown crystal has been characterized by FT-IR). The optical transition and the lower cutoff wavelength of the BH have been identified by UV–vis–NIR studies. Thermo gravimetric analysis and differential thermal analysis have been carried out; the BH was found to be thermally stable up to 104 °C. Powder second harmonic generation (SHG) was investigated to explore its nonlinear optical (NLO) properties. The high SHG is due to one dimensional charge transfer between amine and phenyl group. Both the real ε_r and imaginary ε_i components of the dielectric constant have been calculated as functions of photon energy.     

Isotropic lazurite: A cubic single crystal with an incommensurate three-dimensional modulation of the structure

The incommensurately modulated structure of the isotropic lazurite Na_6.41Ca_1.36K_0.04(Si_6.09Al_5.91)O₂₄(SO₄)_1.73Cl_0.17 from the Ba?kal region is solved in the (3 + 3)-dimensional symmetry group P23(γγ0) [where γ = 0.2154(1)] with the basic unit cell parameter a = 9.077(1) Å. The structure is refined to R ₀ = 0.04 for the main reflections and R ₁ = 0.15 for the satellite reflections. Six modulation waves are directed along the side diagonals of the unit cell. The structural model under investigation is compared with the twin model previously proposed for the same crystal. The structural data obtained are used to construct fragments of the modulated structure. Considering the constructed fragments of the modulated structure, it has become possible for the first time to reproduce and describe the three-dimensional modulation of the framework and to reveal its relation to modulations of intraframework atoms.     

A Czochralski crystal puller automated by the weighing method

The automated crystal growing equipment makes use of a commercial electronic balance equipped with a microprocessor. The mode of operation is explained and experiences got on the occasion of crystal growth experiments are presented.     

Porous glass-ceramics composed of a titanium phosphate crystal skeleton: A review

Bulk microporous glass-ceramics with a skeleton of two types of functional titanium phosphate crystal were prepared by controlled crystallization of RTi₂(PO₄)₃ (

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glasses, and chemical treatment. One crystal is a NASICON-type with a three-dimensional network structure of TiO₆ and PO₄ while the other is a zirconium phosphate-type crystal Ti(HPO₄)₂ · 2H₂O with a two-dimensional layered structure. The mean pore diameter and porosity of 30–60 nm and 40–60 vol.% were achieved. Porous CaTi₄(PO₄)₆ glass-ceramics have excellent properties as supports for immobilization of enzymes, humidity sensors and porous LiTi₂(PO₄)₃ glass-ceramics as ion exchange media. Conspicuous bacteriostatic activities were found for the partially Ag-exchanged porous LiTi₂(PO₄)₃ and Li_1.4Ti_1.6Al_0.4(PO₄)₃. Integrated microporous glass-ceramics with skeletons of LiTi₂(PO₄)₃ (LTP) and Ti(HPO₄)₂ · 2H₂O (TP) crystals were synthesized utilizing a novel discovery that LTP is transformed into TP in acid solution.