Showing papers on "Crystal published in 1999"

Crystal growth

Abstract: This report introduces briefly some concepts and materials on crystal growth presented by Dr. Zhen-yu Zhang from the Oak Ridge (TN) National Laboratory, and Dr. En-ge Wang from the Institute of Physics, Chinese Academy of Sciences, in a session on crystal growth at the first Chinese-American Frontiers of Science Symposium. Crystal growth involves a variety of research fields ranging from surface physics, crystallography, and material sciences to condenser mater physics. Though it has been studied extensively more than 100 years, crystal growth still plays an important role in both theoretical and experimental research fields, as well as in applications. For example, how to growth ideal high Tc superconductor crystal has become an dominant subject both for testing of superconductor theories and physical properties. Furthermore, carbon 60 and carbon nano-tubes have opened a new field to both condensed mater physics and chemistry. From the recent discoveries in high Tc superconductors and C60, which brought the Nobel prize to the pioneer researchers in this field, one can understand the importance of crystal growth today. As the development of scientific instruments and analytical methods, such as x-rays, electron microscopy, NMR, and scanning tunneling microscopy continues, research on crystal growth and structure characterization has entered an atomic level, which makes it possible for further understanding of the physical, chemical, and other properties of the structure nature of various crystals. Especially for the crystals with low dimension and nano-structures, such as carbon nanotubes, blue-light emitting GaN thin films, and magnetic multilayers with giant magneto-resistance, their abnormal properties that have great potential in application can be understood only with the knowledge of structure at the atomic level. Moreover, a further improvement of crystal quality also depends on the structure characterizations. Based on its importance described above, crystal growth had been chosen as one of the topics …

Pyrrolidinium Imides: A New Family of Molten Salts and Conductive Plastic Crystal Phases

Abstract: A new family of molten salts is reported, based on the N-alkyl, N-alkyl pyrrolidinium cation and the bis(trifluoromethane sulfonyl)imide anion. Some of the members of the family are molten at room temperature, while the smaller and more symmetrical members have melting points around 100 °C. Of the room-temperature molten salt examples, the methyl butyl derivative exhibits the highest conductivity; at 2 × 10-3 S/cm this is the highest molten salt conductivity observed to date at room temperature among the ammonium salts. This highly conductive behavior is rationalized in terms of the role of cation planarity. The salts also exhibit multiple crystalline phase behavior below their melting points and exhibit significant conductivity in at least their higher temperature crystal phase. For example, the methyl propyl derivative (mp = 12 °C) shows ion conductivity of 1 × 10-6 S/cm at 0 °C in its higher temperature crystalline phase.

Control of crystal nucleation by patterned self-assembled monolayers

Abstract: An important requirement in the fabrication of advanced inorganic materials, such as ceramics and semiconductors, is control over crystallization1,2,3,4. In principle, the synthetic growth of crystals can be guided by molecular recognition at interfaces5,6,7,8,9,10,11,12,13,14,15,16. But it remains a practical challenge to control simultaneously the density and pattern of nucleation events, and the sizes and orientations of the growing crystals. Here we report a route to crystal formation, using micropatterned self-assembled monolayers17,18, which affords control over all these parameters. We begin with a metal substrate patterned with a self-assembled monolayer having areas of different nucleating activity—in this case, an array of acid-terminated regions separated by methyl-terminated regions. By immersing the patterned substrates in a calcium chloride solution and exposing them to carbon dioxide, we achieve ordered crystallization of calcite in the polar regions, where the rate of nucleation is fastest; crystallization can be completely suppressed elsewhere by a suitable choice of array spacing, which ensures that the solution is undersaturated in the methyl-terminated regions. The nucleation density (the number of crystals formed per active site) may be controlled by varying the area and distribution of the polar regions, and we can manipulate the crystallographic orientation by using different functional groups and substrates.

Mechanism of Zeolite A Nanocrystal Growth from Colloids at Room Temperature

Abstract: The formation and growth of crystal nuclei of zeolite A from clear solutions at room temperature were studied with low-dose, high-resolution transmission electron microscopy in field emission mode and with in situ dynamic light scattering Single zeolite A crystals nucleated in amorphous gel particles of 40 to 80 nanometers within 3 days at room temperature The resulting nanoscale single crystals (10 to 30 nanometers) were embedded in the amorphous gel particles The gel particles were consumed during further crystal growth at room temperature, forming a colloidal suspension of zeolite A nanocrystals of 40 to 80 nanometers On heating this suspension at 80°C, solution-mediated transport resulted in additional substantial crystal growth

Picosecond–milliångström lattice dynamics measured by ultrafast X-ray diffraction

Abstract: Fundamental processes on the molecular level, such as vibrations and rotations in single molecules, liquids or crystal lattices and the breaking and formation of chemical bonds, occur on timescales of femtoseconds to picoseconds. The electronic changes associated with such processes can be monitored in a time-resolved manner by ultrafast optical spectroscopic techniques1, but the accompanying structural rearrangements have proved more difficult to observe. Time-resolved X-ray diffraction has the potential to probe fast, atomic-scale motions2,3,4,5. This is made possible by the generation of ultrashort X-ray pulses6,7,8,9,10, and several X-ray studies of fast dynamics have been reported6,7,8,11,12,13,14,15. Here we report the direct observation of coherent acoustic phonon propagation in crystalline gallium arsenide using a non-thermal, ultrafast-laser-driven plasma — a high-brightness, laboratory-scale source of subpicosecond X-ray pulses16,17,18,19. We are able to follow a 100-ps coherent acoustic pulse, generated through optical excitation of the crystal surface, as it propagates through the X-ray penetration depth. The time-resolved diffraction data are in excellent agreement with theoretical predictions for coherent phonon excitation20 in solids, demonstrating that it is possible to obtain quantitative information on atomic motions in bulk media during picosecond-scale lattice dynamics.

A constitutive model for ferroelectric polycrystals

Abstract: A constitutive model is developed for the non-linear switching of ferroelectric polycrystals under a combination of mechanical stress and electric field. It is envisaged that the polycrystal consists of a set of bonded crystals and that each crystal comprises a set of distinct crystal variants. Within each crystal the switching event, which converts one crystal variant into another, gives rise to a progressive change in remanent strain and polarisation and to a change in the average linear electromechanical properties. It is further assumed that switching is resisted by the dissipative motion of domain walls. The constitutive model for the progressive switching of each crystal draws upon elastic–plastic crystal plasticity theory, and a prescription is given for the tangent moduli of the crystal, for any assumed set of potentially active transformation systems. A self-consistent analysis is used to estimate the macroscopic response of tetragonal crystals (representative of lead titanate) under a variety of loading paths. Also, the evolution of the switching surface in stress-electric field space is calculated. Many of the qualitative features of ferroelectric switching, such as butterfly hysteresis loops, are predicted by the analysis.

Enhanced Piezoelectric Property of Barium Titanate Single Crystals with Engineered Domain Configurations

Abstract: Piezoelectric properties of barium titanate single crystals were investigated at room temperature as a function of crystallographic orientation. When a unipolar electric field was applied along [001], its strain vs electric-field curve showed a large hysteresis, and finally barium titanate crystal became to single-domain state with piezoelectric constant d33 of 125 pC/N over 20 kV/cm. On the other hand, electric-field exposure below 6 kV/cm along [111] resulted in a high d33 of 203 pC/N and a hysteresis-free strain vs electric-field behavior, which suggested the formation of an engineered domain configuration in a tetragonal barium titanate crystal. Moreover, when an electric field over 6 kV/cm was applied along [111], two discontinuous changes were observed in its strain vs electric-field curve. In situ domain observation and Raman measurement under an electric field suggested an electric-field-induced phase transition from tetragonal to monoclinic at around 10 kV/cm, and that from monoclinic to rhombohedral at around 30 kV/cm. Moreover, in a monoclinic barium titanate crystal, electric-field exposure along [111] resulted in the formation of another new engineered domain configuration with d33 of 295 pC/N.

Helical Coordination Polymers from Achiral Components in Crystals. Homochiral Crystallization, Homochiral Helix Winding in the Solid State, and Chirality Control by Seeding

Abstract: An achiral anthracene−pyrimidine derivative (5-(9-anthracenyl)pyrimidine, 1) forms adduct 1·Cd(NO3)2·H2O·EtOH (2) in chiral space group P21. The metal ion is hexacoordinated with two pyrimidine ligands (equatorial cis), water and ethanol (equatorial cis), and two nitrate ions (axial trans). The chirality arises from a pyrimidine−Cd2+ helical array and is preserved not only in each crystal via homochiral interstrand water−nitrate hydrogen bonding but also in all the crystals in the same chirality as a result of single-colony homochiral crystal growth. Compound 1 also forms achiral (Pbca) trihydrate adduct 1·Cd(NO3)2·3H2O (3) having nonhelical pyrimidine−Cd2+ zigzag chains. Achiral zigzag polymer 3 and chiral helical polymer 2 are interconvertible with each other in the solid states upon exchange of volatile ligands (ethanol and water). The helix winding associated with the conversion of adduct 3 to 2 can be made homochiral by seeding.

Crystallographically engineered BaTiO3 single crystals for high-performance piezoelectrics

Abstract: Dielectric and piezoelectric properties of BaTiO3 single crystals polarized along the 〈001〉 crystallographic axes were investigated as a function of temperature and dc bias. Electromechanical coupling (k33)∼85% and piezoelectric coefficients (d33)∼500 pC/N, better or comparable to those of lead-based Pb(Zr, Ti)O3 (PZT), were found from 〈001〉-oriented orthorhombic crystals at 0 °C, as a result of crystallographic engineering. A rhombohedral BaTiO3 crystal polarized along 〈001〉 also exhibited enhanced piezoelectric performance, i.e., k33∼79% and d33∼400 pC/N at −90 °C, superior to PZTs at the same temperature. It was found that the crystal structure determined the (in)stability of the engineered domain state in BaTiO3 single crystals. Rhombohedral (3m) crystals at −100 °C exhibited a stable domain configuration, whereas depoling occurred in crystals in the adjacent orthorhombic phase upon removal of the E field.

Molecular-dynamics simulations of glass formation and crystallization in binary liquid metals: Cu-Ag and Cu-Ni

Abstract: We used molecular dynamics ~MD! to obtain an atomistic description of the melting, glass formation, and crystallization processes in metal alloys. These studies use the quantum Sutton-Chen many-body potentials for Cu, Ni, and Ag to examine the Cu4Ag6 and CuNi alloys. Using cooling rates in the range of 2 310 12 to 4 310 14 K/s, we find that CuNi and pure Cu always form a face-centered-cubic ~fcc! crystal while Cu4Ag6 always forms a glass ~with Tg decreasing as the quench rate increases!. The crystal formers have radius ratios of 1.025 ~CuNi! and 1.00 ~Cu! while the glass former ~CuAg! has a ratio of 1.13, confirming the role of size mismatch in biasing toward glass formation. @S0163-1829~99!05205-4#

Wigner crystal model of counterion induced bundle formation of rodlike polyelectrolytes

Abstract: A simple electrostatic theory of condensation of rodlike polyelectrolytes under influence of polyvalent counterions is proposed. It is based on the idea that counterions form a Wigner crystal on a background of a bundle of rods. It is shown that, depending on a single dimensionless parameter, this can be a densely packed three-dimensional Wigner crystal or a two-dimensional crystal on the rod surfaces. For DNA the location of charge on the spiral results in a model of the one-dimensional Wigner crystal. It is also argued that the Wigner crystal idea can be applied to self-assembly of other polyelectrolytes, for example, colloids and DNA-lipid complexes.

Piezoelectric properties of zirconium-doped barium titanate single crystals grown by templated grain growth

Abstract: Single crystals of Ba(ZrxTi1−x)O3 were grown by templated grain growth (TGG). Millimeter size single crystals of Ba(ZrxTi1−x)O3 were produced by heating a BaTiO3 crystal in contact with a sintered polycrystalline matrix of 4.5, 5.0, or 8.5 mol % Zr-doped barium titanate for 30 h at 1350 °C. To facilitate boundary migration, the ceramic compact was made 3 mol % TiO2 excess. The 4.5 and 5.0 mol % Zr-doped crystals were orthorhombic at room temperature, and for a pseudocubic (001) orientation, they showed remanent polarizations of 13 μC/cm2 and a high field d33 of 340–355 pC/N. The 8.5 mol % Zr-doped crystal [again oriented along the pseudocubic (001)] was rhombohedral at room temperature with a remanent polarization of 10 μC/cm2. A k33 value of 0.74 from resonance measurements was observed for the 4.5 mol % Zr-doped crystal.

Synthesis and Crystallographic Characterization of an Octameric Water Complex, (H2O)8

Abstract: Small water clusters are the subject of considerable theoretical and experimental scrutiny and include a recently isolated water decamer A detailed understanding of the numerous possible structures and stabilities is important for obtaining insight into the nature of water--water interactions in diverse environments Of particular interest are octameric water clusters, (H{sub 2}O){sub 8} A two-to-one combination in acetonitrile of {kappa}{sup 4}-[1,2-bis(2-oxy-2-methylpropanamido)-4,5-dimethoxybenzene]cobaltate(III), [A]{sup {minus}}, with bis-{kappa}{sup 3}-(2,6-diacetamidopyridine)cobalt(II), [B]{sup 2+}, yields the crystalline solvate, [A{sub 2}B]{center_dot}(CH{sub 3}CN){sub 4} On treatment with humid air for 10 to 12 days, [A{sub 2}B]{center_dot}(CH{sub 3}CN){sub 4} forms the [A{sub 2}B](H{sub 2}O){sub 8} complex without crystal decay; both species have been crystallographically characterized

In situ observation of nucleation and crystal growth in zeolite synthesis. A small-angle X-ray scattering investigation in Si-TPA-MFI

Abstract: The formation and consumption of nanometer scale precursor particles during the hydrothermal synthesis of Si-TPA-MFI from a clear solution has been studied in situ using a combination of X-ray scattering techniques and with electron microscpy. The combination of wide-, small-, and ultra-small-angle X-ray scattering allowed us to obtain information on a continuous range of length scales spanning over four orders of magnitude (0.17−6000 nm), covering all particle populations present during the complete course of the crystallization process. The use of high-brilliance synchrotron radiation allows us to perform time-resolved experiments. Two types of precursor particles were observed: 2.8 nm sized primary units and aggregates (≈10 nm). Variation of the alkalinity of the synthesis mixture revealed a strong correlation between the concentration of the aggregates and the rate of the crystal nucleation. The presence of the 2.8 nm sized primary units appears to be independent on the alkalinity. The addition of se...

Self-waveguided blue light emission in p-sexiphenyl crystals epitaxially grown by mask-shadowing vapor deposition

Abstract: Highly polarized and self-waveguided blue light emission was observed in oriented organic crystals of p-sexiphenyl (6P). The 6P molecules were epitaxially grown in needlelike crystals with a submillimeter length by mask-shadowing vapor deposition on the KCl (001) surface. In the crystals, the molecular axes are oriented parallel to the [110] direction of the KCl substrate and perpendicular to the needle axis of the crystal. Under ultraviolet excitation, the blue light emission was confined within the crystal and self-waveguided along the needle axis with the transverse-electric mode, then radiated from the tips of the needles. This self-waveguided emission in the crystal was based on the uniaxially oriented transition dipoles which lay on the KCl surface and were aligned perpendicular to the needle axis in the crystal.

Photochromism of 1,2-Bis(2,5-dimethyl-3-thienyl)perfluoro- cyclopentene in a Single Crystalline Phase

Abstract: 1,2-Bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene (1a) was found to undergo photochromism in a single crystalline phase. Upon irradiation with ultraviolet light the colorless crystal turned red with keeping the crystal shape. The red color is due to the closed-ring form 1b. The red color was bleached by irradiation with visible light (λ > 450 nm). The intensity of the red color observed under polarized light dramatically changed by rotating the crystal sample, and the order parameter was as high as 0.84. The high order parameter confirmed that the molecules undergo photochromism in the crystalline lattice. The direction of the electronic transition moment of 1b estimated from the absorption anisotropy at 535 nm agreed with the long axis of 1a packed in the crystal, which was determined by X-ray crystallographic analysis. The movement of each atom of the molecule in the crystal during the cyclization reaction was estimated by comparing the structures of 1a and 1b, both of which were determined by X-ray ...

Self-Assembly of Zinc Oxide Thin Films Modified with Tetrasulfonated Metallophthalocyanines by One-Step Electrodeposition

Abstract: Cathodic electrodeposition in an aqueous mixed solution of zinc nitrate and water-soluble tetrasulfonated metallophthalocyanines (TSPcMs), in which M = Zn(II) (TSPcZn), Al(III)[OH] (TSPcAl), or Si(IV)[OH]2 (TSPcSi), resulted in a self-assembled growth of zinc oxide (ZnO) thin films whose surface is modified by TSPcMs. It has been found that the adsorption of TSPcM onto the growing surface of ZnO strongly affects the crystal growth and the orientation of the ZnO crystallites. The effect was most prominently seen with TSPcSi, creating a film looking like stacking disks aligned perpendicular to the substrate. Crystallographic studies by X-ray diffraction and TEM observation coupled with the selected area electron beam diffraction have revealed that thin platelike crystals, whose planes and edges correspond to the (002) and (100) crystal faces, respectively, are aligned in the same orientation around the c-axis within the stacks. The evolution of this unique structure is interpreted as arising from the prefer...

Systematics of calcium partitioning between olivine and silicate melt: implications for melt structure and calcium content of magmatic olivines

Abstract: A systematic characterization of the chemical factors that control calcium partitioning between olivine and melt in a magmatic environment was undertaken using experiments performed on compositionally simple systems (CaO-MgO-SiO2, CaO-MgO-Al2O3-SiO2, CaO-MgO-Al2O3-SiO2-Cr2O3, CaO-MgO-Al2O3-SiO2-TiO2, CaO-MgO-Al2O3-SiO2-Na2O, CaO-MgO-Al2O3-SiO2-FeO, CaO-MgO-Al2O3-SiO2-FeO-Na2O) over a wide range of temperature (1050–1530 °C) at one bar pressure. The calcium concentration of olivines is shown to be dependent not only on the forsterite content of the olivine but to a large extent on melt composition. For a fixed CaO content of the melt, these results show that the CaO concentration of olivine is strongly sensitive to the amount of alumina, alkali and ferrous iron present in the coexisting melt. Oxygen fugacity and temperature are not found directly to affect Ca partitioning. It is thus proposed that the systematic variations of the calcium content of olivine may be used as an “in-situ chemical potentiometer” of the lime activity of the melt. Based upon these data in synthetic systems, an empirical model describing Ca partitioning between olivine and melt is developed. When applied to natural olivines this model reproduces their Ca content, where melt composition is known, to within ±10% relative. The model may therefore be used to predict changes in melt composition during olivine crystallization and/or to assess whether an olivine is in equilibrium with its host magma. Finally, the wide range of Ca partitioning observed at fixed crystal composition confirms that minor element partitioning between crystal and melt cannot be predicted from the physical characteristics of the crystal alone, and that the non-ideality of the melt has to be taken into account.

Enhanced light amplification due to group-velocity anomaly peculiar to two- and three-dimensional photonic crystals

Abstract: An analytical expression was derived for light amplification by stimulated emission in arbitrary photonic crystals, which showed and enhancement due to small group velocity. This enhancement was evaluated quantitatively for a two-dimensional crystal with a finite thickness, and an extremely large enhancement due to group-velocity anomaly peculiar to two- and three-dimensional crystals was found even for quite a thin crystal.

GaN crystal film, a group III element nitride semiconductor wafer and a manufacturing process therefor

Abstract: A GaN crystal film having a mask patterned in a stripe for forming multiple growing areas on a sapphire substrate and coalesced GaN crystals covering the mask dividing the areas, grown from the neighboring growing areas, comprising defects where multiple dislocations along with the stripe are substantially aligned with the normal line of the substrate, in the crystal areas over the mask, and dislocations propagating in substantially parallel with the substrate surface while, in the vicinity of the areas where the crystals are coalesced over the mask, propagating substantially in the normal line of the substrate surface, and a manufacturing process therefor. According to this invention, there can be provided a GaN crystal film in which strain, defects and dislocations are reduced and which tends not to generate cracks.

Single crystal superconductor nanowires by electrodeposition

Abstract: Superconducting Pb wires (diameter∼50 nm) have been prepared by pulse electrodeposition in nanoporous membranes. Single crystal or polycrystalline nanowires may be grown selectively and reproducibly depending on the pulse parameters. Unexpectedly, the growth of single crystal wires requires a greater departure from equilibrium conditions (greater overpotential) than the growth of polycrystalline ones. The importance of controlling the crystal texture is demonstrated by measurements of the superconducting transition temperature Tc which give significantly different results for polycrystalline and single crystal nanowires.

Crystal engineering : the design and application of functional solids

Abstract: Preface. Crystal Engineering: A Case Study K.R. Seddon. The Chemical Bond in Molecules and Solids R.M. Lynden-Bell. Intermolecular Forces: Their Origin, Strength and Significance A.D. Buckingham. Molecular Mechanics and Crystal Engineering C.B. Aakeroy, R.E. Boyett. Developing a Semiempirical Method J.J.P. Steward, A.C. Stewart. Ab initio Calculations: A User's Guide T.A. Evans. Computational Studies of Molecular Recognition from Alkane Dimers to Protein-Ligand Complexes W.L. Jorgensen, et al. Crystal Growth: From the Classical to Molecular Description N. Blagden. Chemical Crystallography in Crystal Engineering R.D. Robers. The Heart of the Matter: Spectroscopy with Neutrons J. Tomkinson. Applications of Solid State NMR Spectroscopy to the Study of Crystalline Materials J.A. Ripmeester, C.I. Ratcliffe. Thermal Properties of Materials M.A. White. Orientationally Disordered Solids R.M. Lynden-Bell. Hydrogen-bonding in Solids: Some Strategies and Aspects of Crystal Engineering C.B. Aakeroy. Polymorphism and Pseudopolymorphism in Organic Crystals: A Cambridge Structural Database Study J.A.R.P. Sarma, G.R. Desiraju. Molecular Recognition: Synthetic Approaches to Artificial Receptors E. Fan, A.D. Hamilton. Crystal Engineering Based on Diffraction Studies of Supramolecular Compounds J.L. Atwood. Coordination Polymers M.J. Zaworotko. Chemically Engineering the Metallic, Insulating and Superconducting States of Matter P.P. Edwards. Multi-sublattice (Intergrowth) Structures and the Design of Functional Solids P. Coppens. Crystal Design in Zeolite Synthesis D.E.W. Vaughan. Crystal Engineering: A Bibliography K.R. Seddon. Afterword R.M. Lynden-Bell. Index.

Effect of different crystal faces on experimental interaction force and aggregation of hematite

Abstract: Charging is a basic property of the solid/solution interface of minerals. The charging at different crystal faces depends on the surface chemical composition, that is, the type and number of proton-reactive surface groups. Atomic force microscopy has provided direct information on the pH-dependent charging properties of individual crystal faces (Eggleston and Jordan, Geochim. Cosmochim. Acta, 1998) of hematite (001 face) and quartz (101 face). This promising scanning force technique may enable the testing of structure−reactivity relations as applied in the MUlti SIte Complexation model (MUSIC). The published pH-dependent variation of the interaction forces has been evaluated. The large experimental difference in the pH dependence of the interaction force is in accord with the expected proton affinity behavior of both crystal faces, as predicted with the MUSIC model. The reactivity of the 001 face of hematite is quite exceptional, because the surface groups only charge at extremely high or low pH values in...

Directed nucleation of calcite at a crystal-imprinted polymer surface

Abstract: The finely tuned properties of natural biominerals and composites reflect the remarkable level of control that is exercised over the size, shape and organization of the constituent crystals1,2,3,4. Achieving this degree of control over synthetic materials might therefore lead to superior material properties. Organic small molecules, polymers or surfactant mesophases have been used to guide the growth and morphology of inorganic materials via steric constraints or structure-directing interactions5,6,7,8,9,10,11,12,13,14,15,16. Here we show that synthetic polymers can be imprinted with motifs of crystal surfaces so as to template the growth of specific crystal phases. Our polymers, imprinted with calcite, are able to induce the nucleation of calcite under conditions favouring the growth of aragonite (another polymorph of calcium carbonate). The synthesis of the polymers, based on the principles of molecular imprinting17,18,19,20, involves the adsorption of functional monomers to a calcite surface, followed by co-polymerization with a crosslinker to create an imprint of the crystal surface. Subsequent removal of the calcite template yields a polymer matrix with a surface functionality mirroring the crystal face and able to promote the nucleation of calcite. We expect that the molecular-imprinting approach to directed nucleation can be applied to crystals other than calcite.