Showing papers on "Crystal published in 2011"
TL;DR: Several crystal chemical properties appear to promote the high Li-ion conductivity in cubic Al-containing Li(7)La(3)Zr(2)O(12) garnet, which is the best conducting Li-oxide garnet discovered to date.
Abstract: Recent research has shown that certain Li-oxide garnets with high mechanical, thermal, chemical, and electrochemical stability are excellent fast Li-ion conductors. However, the detailed crystal chemistry of Li-oxide garnets is not well understood, nor is the relationship between crystal chemistry and conduction behavior. An investigation was undertaken to understand the crystal chemical and structural properties, as well as the stability relations, of Li7La3Zr2O12 garnet, which is the best conducting Li-oxide garnet discovered to date. Two different sintering methods produced Li-oxide garnet but with slightly different compositions and different grain sizes. The first sintering method, involving ceramic crucibles in initial synthesis steps and later sealed Pt capsules, produced single crystals up to roughly 100 μm in size. Electron microprobe and laser ablation inductively coupled plasma mass spectrometry (ICP-MS) measurements show small amounts of Al in the garnet, probably originating from the crucible...
561 citations
TL;DR: Two unexpected orthorhombic high-pressure structures Aba2-40 and Cmca-56 are reported, by using a newly developed particle swarm optimization technique on crystal structure prediction, and it is predicted that a local trigonal planar structural motif adopted by CmCA-56 exists in a wide pressure range of 85-434 GPa, favorable for the weak metallicity.
Abstract: Under high pressure, "simple" lithium (Li) exhibits complex structural behavior, and even experiences an unusual metal-to-semiconductor transition, leading to topics of interest in the structural polymorphs of dense Li. We here report two unexpected orthorhombic high-pressure structures Aba2-40 (40 atoms/cell, stable at 60-80 GPa) and Cmca-56 (56 atoms/cell, stable at 185-269 GPa), by using a newly developed particle swarm optimization technique on crystal structure prediction. The Aba2-40 having complex 4- and 8-atom layers stacked along the b axis is a semiconductor with a pronounced band gap >0.8 eV at 70 GPa originating from the core expulsion and localization of valence electrons in the voids of a crystal. We predict that a local trigonal planar structural motif adopted by Cmca-56 exists in a wide pressure range of 85-434 GPa, favorable for the weak metallicity.
472 citations
TL;DR: The morphology design of [Cu(3)(btc)(2)](n) (btc = benzene-1,3,5-tricarboxylate) by the coordination modulation method (modulator = n-dodecanoic acid or lauric acid) successfully led to designed crystal morphologies with oriented growth on bare substrates.
Abstract: The design of crystal morphology, or exposed crystal facets, has enabled the development (e.g., catalytic activities, material attributes, and oriented film formation) of porous coordination polymers (PCPs) without changing material compositions. However, because crystal growth mechanisms are not fully understood, control of crystal morphology still remains challenging. Herein, we report the morphology design of [Cu3(btc)2]n (btc = benzene-1,3,5-tricarboxylate) by the coordination modulation method (modulator = n-dodecanoic acid or lauric acid). A morphological transition (octahedron–cuboctahedron–cube) in the [Cu3(btc)2]n crystal was observed with an increase in concentration of the modulator. By suitably defining a coarse-grained standard unit of [Cu3(btc)2]n as its cuboctahedron main pore and determining its attachment energy on crystal surfaces, Monte Carlo coarse-grain modeling revealed the population and orientation of carboxylates and elucidated an important role of the modulator in determining the...
363 citations
TL;DR: In this article, a facile synthesis method using surfactant cetyltrimethylammonium bromide (CTAB) as a capping agent for controlling the crystal size and morphology of zeolitic imidazolate framework-8 (ZIF-8) crystals in aqueous systems is presented.
Abstract: Herein we report a facile synthesis method using surfactant cetyltrimethylammonium bromide (CTAB) as a capping agent for controlling the crystal size and morphology of zeolitic imidazolate framework-8 (ZIF-8) crystals in aqueous systems. The particle sizes can be precisely adjusted from ca. 100 nm to 4 μm, and the morphology can be changed from truncated cubic to rhombic dodecahedron.
353 citations
TL;DR: In this article, the authors studied the crystallization behavior of colloidal cubes by means of tunable depletion interactions and found that the cubes self-organize into crystals with a simple cubic symmetry, which is set by the size of the depletant.
Abstract: We have studied the crystallization behavior of colloidal cubes by means of tunable depletion interactions. The colloidal system consists of novel micron-sized cubic particles prepared by silica deposition on hematite templates and various non-adsorbing watersoluble polymers as depletion agents. We have found that under certain conditions the cubes self-organize into crystals with a simple cubic symmetry, which is set by the size of the depletant. The dynamic of crystal nucleation and growth is investigated, monitoring the samples in time by optical microscopy. Furthermore, by using temperature sensitive microgel particles as depletant it is possible to fine tune depletion interactions to induce crystal melting. Assisting crystallization with an alternating electric field improves the uniformity of the cubic pattern allowing the preparation of macroscopic (almost defect-free) crystals that show visible Bragg colors.
342 citations
TL;DR: A simple wet-chemical process to prepare porous CuO nanobelts (NBs) with high surface area and small crystal grains mixed with carbon nanotubes in an appropriate ratio to fabricate pseudocapacitor electrodes with stable cycling performances, which showed a series of high energy densities at different power densities.
Abstract: We report a simple wet-chemical process to prepare porous CuO nanobelts (NBs) with high surface area and small crystal grains. These CuO NBs were mixed with carbon nanotubes in an appropriate ratio to fabricate pseudocapacitor electrodes with stable cycling performances, which showed a series of high energy densities at different power densities, for example, 130.2, 92, 44, 25, and 20.8 W h kg−1 at power densities of 1.25, 6.25, 25, and 50 k Wh kg−1, respectively. CuO-on-single-walled carbon nanotube (SWCNT) flexible hybrid electrodes were also fabricated using the SWCNT films as current collectors. These flexible electrodes showed much higher specific capacitance than that of electrodes made of pure SWCNTs and exhibited more stable cycling performance, for example, effective specific capacitances of >62 F g−1 for the hybrid electrodes after 1000 cycles in 1 M LiPF6/EC:DEC at a current density of 5 A g−1 and specific capacitance of only 23.6 F g−1 for pure SWCNT electrodes under the same testing condition.
327 citations
TL;DR: Stoichiometric copper(I) selenide nanoparticles have been synthesized using the hot injection method and enhanced electronic properties can be explained by the oxidation of Cu(+) and Se(2-) on the nanoparticle surface, ultimately leading to a solid-state conversion of the core from monoclinic Cu(2)Se to cubic Cu(1.8)Se.
Abstract: Stoichiometric copper(I) selenide nanoparticles have been synthesized using the hot injection method. The effects of air exposure on the surface composition, crystal structure, and electronic properties were monitored using X-ray photoelectron spectroscopy, X-ray diffraction, and conductivity measurements. The current−voltage response changes from semiconducting to ohmic, and within a week a 3000-fold increase in conductivity is observed under ambient conditions. The enhanced electronic properties can be explained by the oxidation of Cu+ and Se2− on the nanoparticle surface, ultimately leading to a solid-state conversion of the core from monoclinic Cu2Se to cubic Cu1.8Se. This behavior is a result of the facile solid-state ionic conductivity of cationic Cu within the crystal and the high susceptibility of the nanoparticle surface to oxidation. This regulated transformation is appealing as one could envision using layers of Cu2Se nanoparticles as both semiconducting and conducting domains in optoelectronic...
312 citations
TL;DR: Results suggest that {001} surfaces can be considered essentially as oxidation sites with a key role in the photoxidation, while {101} surfaces provide reductive sites which do not directly assist the oxidative processes.
Abstract: The promising properties of anatase TiO2 nanocrystals exposing specific surfaces have been investigated in depth both theoretically and experimentally. However, a clear assessment of the role of the crystal faces in photocatalytic processes is still under debate. In order to clarify this issue, we have comprehensively explored the properties of the photogenerated defects and in particular their dependence on the exposed crystal faces in shape-controlled anatase. Nanocrystals were synthesized by solvothermal reaction of titanium butoxide in the presence of oleic acid and oleylamine as morphology-directing agents, and their photocatalytic performances were evaluated in the phenol mineralization in aqueous media, using O2 as the oxidizing agent. The charge-trapping centers, Ti3+, O–, and O2–, formed by UV irradiation of the catalyst were detected by electron spin resonance, and their abundance and reactivity were related to the exposed crystal faces and to the photoefficiency of the nanocrystals. In vacuum c...
306 citations
TL;DR: It is demonstrated that it is possible to convert CdSe nanocrystals of a given size, shape, and crystal structure into ZnSe Nanocrystals that preserve all these characteristics of the starting particles through a sequence of two cation exchange reactions.
Abstract: We demonstrate that it is possible to convert CdSe nanocrystals of a given size, shape (either spherical or rod shaped), and crystal structure (either hexagonal wurtzite, i.e., hexagonal close packed (hcp), or cubic sphalerite, i.e., face-centered cubic (fcc)), into ZnSe nanocrystals that preserve all these characteristics of the starting particles (i.e., size, shape, and crystal structure), via a sequence of two cation exchange reactions, namely, Cd2+ ⇒Cu+ ⇒Zn2+. When starting from hexagonal wurtzite CdSe nanocrystals, the exchange of Cd2+ with Cu+ yields Cu2Se nanocrystals in a metastable hexagonal phase, of which we could follow the transformation to the more stable fcc phase for a single nanorod, under the electron microscope. Remarkably, these metastable hcp Cu2Se nanocrystals can be converted in solution into ZnSe nanocrystals, which yields ZnSe nanocrystals in a pure hcp phase.
286 citations
TL;DR: Here, molecular dynamics is used to show that polished diamond undergoes an sp(3)-sp(2) order-disorder transition resulting in an amorphous adlayer with a growth rate that strongly depends on surface orientation and sliding direction, in excellent correlation with experimental wear rates.
Abstract: Diamond is the hardest material on Earth. Nevertheless, polishing diamond is possible with a process that has remained unaltered for centuries and is still used for jewellery and coatings: the diamond is pressed against a rotating disc with embedded diamond grit. When polishing polycrystalline diamond, surface topographies become non-uniform because wear rates depend on crystal orientations. This anisotropy is not fully understood and impedes diamond's widespread use in applications that require planar polycrystalline films, ranging from cutting tools to confinement fusion. Here, we use molecular dynamics to show that polished diamond undergoes an sp(3)-sp(2) order-disorder transition resulting in an amorphous adlayer with a growth rate that strongly depends on surface orientation and sliding direction, in excellent correlation with experimental wear rates. This anisotropy originates in mechanically steered dissociation of individual crystal bonds. Similarly to other planarization processes, the diamond surface is chemically activated by mechanical means. Final removal of the amorphous interlayer proceeds either mechanically or through etching by ambient oxygen.
276 citations
TL;DR: The synthesis of large single crystals of a new FeSe layer superconductor Cs( 0.8)(FeSe(0.98))(2) is reported on, which shows a slightly lower superconducting transition temperature and the T(c) dependence on the anion height was found to be analogous to those reported for As-containing Fe superconductors and Fe(Se(1 - x)Ch(x)), where Ch = Te, S.
Abstract: We report on the synthesis of large single crystals of a new FeSe layer superconductor Cs0.8(FeSe0.98)2. X-ray powder diffraction, neutron powder diffraction and magnetization measurements have been used to compare the crystal structure and the magnetic properties of Cs0.8(FeSe0.98)2 with those of the recently discovered potassium intercalated system KxFe2Se2. The new compound, Cs0.8(FeSe0.98)2, shows a slightly lower superconducting transition temperature (Tc = 27.4 K) in comparison to 29.5 in (K0.8(FeSe0.98)2). The volume of the crystal unit cell increases by replacing K by Cs—the c parameter grows from 14.1353(13) to 15.2846(11) A. For the alkali metal intercalated layered compounds known so far, (K0.8Fe2Se2 and Cs0.8(FeSe0.98)2), the Tc dependence on the anion height (distance between Fe layers and Se layers) was found to be analogous to those reported for As-containing Fe superconductors and Fe(Se1 − xChx), where Ch = Te, S.
TL;DR: In this article, the photocatalytic activity of Cu-doped ZnO nanoparticles was evaluated for methyl orange degradation under UV irradiation and the results showed that the nanoparticles with wurtzite phase were 32.0 and 28.5 nm.
TL;DR: How submicrometer hard x-ray beams with the ability to penetrate tens to hundreds of micrometers into most materials and with the able to determine local composition, chemistry, and (crystal) structure can characterize buried sample volumes and small samples in their natural or extreme environments is described.
Abstract: X-ray microbeams are an emerging characterization tool with broad implications for science, ranging from materials structure and dynamics, to geophysics and environmental science, to biophysics and protein crystallography. We describe how submicrometer hard x-ray beams with the ability to penetrate tens to hundreds of micrometers into most materials and with the ability to determine local composition, chemistry, and (crystal) structure can characterize buried sample volumes and small samples in their natural or extreme environments. Beams less than 10 nanometers have already been demonstrated, and the practical limit for hard x-ray beam size, the limit to trace-element sensitivity, and the ultimate limitations associated with near-atomic structure determinations are the subject of ongoing research.
TL;DR: It is found that mixtures of these phases can exhibit up to 2 orders of magnitude higher resistivity than single-phase nanowires, with a temperature-activated transport mechanism, but it is also found that defects in the form of stacking faults and twin planes do not significantly affect the resistivity.
Abstract: We report a systematic study of the relationship between crystal quality and electrical properties of InAs nanowires grown by MOVPE and MBE, with crystal structure varying from wurtzite to zinc blende. We find that mixtures of these phases can exhibit up to 2 orders of magnitude higher resistivity than single-phase nanowires, with a temperature-activated transport mechanism. However, it is also found that defects in the form of stacking faults and twin planes do not significantly affect the resistivity. These findings are important for nanowire-based devices, where uncontrolled formation of particular polytype mixtures may lead to unacceptable device variability.
TL;DR: This system provides a unique model for understanding biomineral formation, giving insight into both the mechanism of occlusion of biomacromolecules within single crystals, and the relationship between the macroscopic mechanical properties of a crystal and its microscopic structure.
Abstract: Biominerals exhibit morphologies, hierarchical ordering and properties that invariably surpass those of their synthetic counterparts. A key feature of these materials, which sets them apart from synthetic crystals, is their nanocomposite structure, which derives from intimate association of organic molecules with the mineral host. We here demonstrate the production of artificial biominerals where single crystals of calcite occlude a remarkable 13 wt% of 20 nm anionic diblock copolymer micelles, which act as 'pseudo-proteins'. The synthetic crystals exhibit analogous texture and defect structures to biogenic calcite crystals and are harder than pure calcite. Further, the micelles are specifically adsorbed on {104} faces and undergo a change in shape on incorporation within the crystal lattice. This system provides a unique model for understanding biomineral formation, giving insight into both the mechanism of occlusion of biomacromolecules within single crystals, and the relationship between the macroscopic mechanical properties of a crystal and its microscopic structure.
TL;DR: The atomic dynamics of the glass to that of the relevant crystal suggests the identical nature of the two features, including the boson peak, which matches the TA singularity in energy and height.
Abstract: We compare the atomic dynamics of the glass to that of the relevant crystal. In the spectra of inelastic scattering, the boson peak of the glass appears higher than the transverse acoustic (TA) singularity of the crystal. However, the density of states shows that they have the same number of states. Increasing pressure causes the transformation of the boson peak of the glass towards the TA singularity of the crystal. Once corrected for the difference in the elastic medium, the boson peak matches the TA singularity in energy and height. This suggests the identical nature of the two features.
TL;DR: In this paper, the possibility of a reversible liquid-liquid transition in supercooled water and related systems was examined using numerical simulation and it was shown that at no range of temperatures and pressures is there more than a single liquid basin, even at conditions where amorphous behavior is unstable with respect to the crystal.
Abstract: We use numerical simulation to examine the possibility of a reversible liquid-liquid transition in supercooled water and related systems. In particular, for two atomistic models of water, we have computed free energies as functions of multiple order parameters, where one is density and another distinguishes crystal from liquid. For a range of temperatures and pressures, separate free energy basins for liquid and crystal are found, conditions of phase coexistence between these phases are demonstrated, and time scales for equilibration are determined. We find that at no range of temperatures and pressures is there more than a single liquid basin, even at conditions where amorphous behavior is unstable with respect to the crystal. We find a similar result for a related model of silicon. This result excludes the possibility of the proposed liquid-liquid critical point for the models we have studied. Further, we argue that behaviors others have attributed to a liquid-liquid transition in water and related systems are in fact reflections of transitions between liquid and crystal.
TL;DR: For the investigation of the individual polymorphs (crystal and electronic structures), the GGA+U/LDA+U method and the HSE06 functional are in better agreement with experiments compared to the conventional GGA or LDA.
Abstract: This work investigates crystal lattice, electronic structure, relative stability, and high pressure behavior of TiO(2) polymorphs (anatase, rutile, and columbite) using the density functional theory (DFT) improved by an on-site Coulomb self-interaction potential (DFT+U). For the latter the effect of the U parameter value (0 < U < 10 eV) is analyzed within the local density approximation (LDA+U) and the generalized gradient approximation (GGA+U). Results are compared to those of conventional DFT and Heyd-Scuseria-Ernzehorf screened hybrid functional (HSE06). For the investigation of the individual polymorphs (crystal and electronic structures), the GGA+U/LDA+U method and the HSE06 functional are in better agreement with experiments compared to the conventional GGA or LDA. Within the DFT+U the reproduction of the experimental band-gap of rutile/anatase is achieved with a U value of 10/8 eV, whereas a better description of the crystal and electronic structures is obtained for U < 5 eV. Conventional GGA∕LDA and HSE06 fail to reproduce phase stability at ambient pressure, rendering the anatase form lower in energy than the rutile phase. The LDA+U excessively stabilizes the columbite form. The GGA+U method corrects these deficiencies; U values between 5 and 8 eV are required to get an energetic sequence consistent with experiments (E(rutile) < E(anatase) < E(columbite)). The computed phase stability under pressure within the GGA+U is also consistent with experimental results. The best agreement between experimental and computed transition pressures is reached for U ≈ 5 eV.
TL;DR: In this article, a trichromatic white-light emitting diode was fabricated by integrating a 380 nm near-ultraviolet (n-UV) chip comprising yellow-emitting (Ca0.5Sr0.02Mn2+ and blue-emining (Ca 0.5Mg0.007Eu2+) phosphors into a single package.
Abstract: Two series of single-composition (Ca,Mg,Sr)9Y(PO4)7:Eu2+ and (Ca0.5Sr0.5)9Y(PO4)7:Eu2+,Mn2+ phosphors were synthesized via high-temperature solid-state reactions. Their emission colors could be tuned from blue to green and eventually to red through tuning the crystal field splitting and energy transfer. On examining the Mn2+ concentration-dependent photoluminescence properties, we found that co-doping with Mn2+ would lead to a change in Eu2+/Eu3+ ratio. Moreover, an energy transfer from Eu2+ to Mn2+ occurs because of the spectral overlap between the emission band of Eu2+ and the excitation band of Mn2+. The resonance-type energy transfer via a dipole–quadrupole interaction mechanism was supported by decay lifetime data and the critical distance of energy transfer was calculated to be 11.09 A. A trichromatic white-light emitting diode was fabricated by integrating a 380 nm near-ultraviolet (n-UV) chip comprising yellow-emitting (Ca0.5Sr0.5)9Y(PO4)7:0.007Eu2+,0.02Mn2+ and blue-emitting (Ca0.5Mg0.5)9Y(PO4)7:0.007Eu2+ phosphors into a single package. Such a composite device emitted white light with a correlated color temperature of 6303 K, a color rendering index of 87.4, and color coordinates (0.314, 0.348) close to those of ideal white light. The results suggest that a phosphor blend of (Ca0.5Sr0.5)9Y(PO4)7:0.007Eu2+,0.02Mn2+ and (Ca0.5Mg0.5)9Y(PO4)7:0.007Eu2+ is potentially useful for white n-UV light-emitting diodes (LEDs).
TL;DR: In this paper, a spherical colloid with a nematic liquid crystal is used to control the number and orientation of the defects in the crystal, which could be useful for engineering the microstructure of colloidal materials.
Abstract: Coating a spherical colloid with a nematic liquid crystal causes frustration-induced defects in the crystal. The thickness of this coating can be used to systematically control the number and orientation of these defects, which could be useful for engineering the microstructure of colloidal materials.
TL;DR: In this article, the authors used differential fast scanning calorimetry (DFSC) for a new look at the crystal growth of poly( ǫ-caprolactone) (PCL) from 185k to 330k, close to the equilibrium melting temperature.
TL;DR: In this paper, the influence of the surface structure of copper single crystals on the growth of large area monolayer graphene by chemical vapor deposition (CVD) in ultra-high vacuum (UHV).
TL;DR: The demonstration of reversible twisting without the need for specialized irradiation conditions represents a new type of photoinduced motion in molecular crystals and may provide new modes of operation for photomechanical actuators.
Abstract: 9-Anthracenecarboxylic acid, a molecule that undergoes a reversible [4 + 4] photodimerization, is prepared in the form of oriented crystalline microribbons. When exposed to spatially uniform light irradiation, these photoreactive ribbons rapidly twist. After the light is turned off, they relax back to their original shape over the course of minutes. This photoinduced motion can be repeated for multiple cycles. The final twist period and cross-sectional dimensions of individual microribbons are measured using a combination of atomic force and optical microscopies. Analysis of this data suggests that the reversible twisting involves the generation of interfacial strain within the ribbons between unreacted monomer and photoreacted dimer regions, with an interaction energy on the order of 3.4 kJ/mol. The demonstration of reversible twisting without the need for specialized irradiation conditions represents a new type of photoinduced motion in molecular crystals and may provide new modes of operation for photo...
TL;DR: In this article, the authors investigated the self-organization of the derivatives in poly(L-lactide (PLLA) melt and its subsequent effect on the crystal morphology of PLLA though it is very important for the macroscopic performance.
Abstract: In the past few years, poly(L-lactide) (PLLA) has attracted increasing attention due to its excellent biocompatibility and processability. As an eco-friendly thermoplastic polyester, PLLA can be produced completely from renewable sources, such as corn, and degrade into carbon dioxide and water in soil or a composting environment. This sustainability makes PLLA a suitable alternative to traditional petrochemical-based polymers where their recycling still remains a challenge. PLLA has good mechanical properties at room temperature, such as high tensile strength and elastic modulus, but its article prepared by practical processing methods (e.g., injection molding) exhibits poor mechanical performance above its glass transition temperature (around 60 C) since it remains almost amorphous after processing due to its slow crystallization rate.Moreover, PLLA is brittle and its long-term behavior is poor because of a pronounced creep. The crystallization can restrict molecular mobility and then improve the long-term performance. Obviously, PLLA article with suitable crystallinity is required in many commercial applications. On the other hand, the mechanical, thermal properties, and even biodegradability of such semicrystalline polymer have been demonstrated to be strongly dependent on the crystal morphology and structure. Therefore, the realization of effective control on the crystal superstructure consisting of crystalline lamella, such as spherulites and shish-kebab structure, is of great scientific and technical significance because it might provide a route to prepare PLLA products with excellent macroscopic performance. In most cases, isotropic spherulite-like crystal morphology is observed for semicrystalline polymer including PLLA, while shish-like fibril crystals are often obtained from the sheared melt. Many researchers reported that adding nucleating agent is a useful method for controlling the crystal superstructure of polymer, such as polyolefins. For example, the exclusive formation of bundle-like superstructure for β-phase and the radiating, spherulitic superstructure for R-phase in polypropylene (PP) can be induced by adding highly active β-form and R-form nucleating agent, respectively. Moreover, the assembled structure could vary with its concentration and the thermal conditions during melting and crystallization if the nucleating agent is partially or completely dissolved in the polymer melt and recrystallize during cooling. As a result, different superstructures of PP could be induced. For instance, sorbitol-based nucleating agents, such as well-known 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS), can self-organize into nanofibils on cooling, and then lateral growth of PP lamellae occurs orthogonally to the fibrils, forming a typical shish-kebab structure. Thus, adding nucleating agent with the ability of self-organizing in polymer melt is believed to be an important method to manipulate crystal morphology as well as properties of polymer articles. Similar to DMDBS, 1,3,5-benzenetricarboxylamide derivatives, another family of nucleating agents for PP, are also found to be capable of self-organizing in PPmelt through intermolecular hydrogen bonding of the amides in the form of a three-dimensional fibrillar network. Very recently, the derivatives have been successfully used to enhance the crystallization of PLLA. However, no attention has been paid to the self-organization of the derivatives in PLLA melt and its subsequent effect on the crystal morphology of PLLA though it is very important for the macroscopic performance. Therefore, in this Communication, we use one of the above derivatives, i.e., N,N0,N00-tricyclohexyl-1,3,5-benzenetricarboxylamide (TMC-328), as a model to tailor the crystal superstructure of PLLA, and three crystal morphologies including cone-like, shish-kebab, and needle-like structures have been successfully obtained for the first time using melt crystallization. Furthermore, the evolution of crystal morphology during crystallization is investigated using in-situ POM and rheological measurement.
TL;DR: In this paper, the NiCo2 alloys with different shapes (Ni33.8Co66.2 dendrites and Ni33.4Co 66.6) were synthesized by solvothermal routes.
Abstract: Dendritic Ni33.8Co66.2 alloy microstructures with hexagonal closed-packed phase have been prepared in large-scale by a simple and facile solution phase chemical route, while flowerlike Ni33.4Co66.6 in size of 2.5–5.5 μm was synthesized by solvothermal routes. Experimental results show that the reaction temperature, total concentration of [Ni2+] + [Co2+], and kinds of solvent and surfactants are key factors for controlling the morphology and crystal phase of the NiCo alloy. The possible formation mechanism for the Ni33.8Co66.2 dendrites has been discussed. Magnetic measurements revealed that both of the NiCo2 alloys obtained are ferromagnetic at room temperature. The saturation magnetization value of the Ni33.8Co66.2 dendrites (163.55 emu/g) is lower than that of the flowerlike Ni33.4Co66.6 (195.79 emu/g), but the Ni33.8Co66.2 dendritic structures exhibit an enhanced coercivity value. NiCo2 alloys with different shapes (Ni33.8Co66.2 dendrites and flowerlike Ni33.4Co66.6) have been used as reusable heteroge...
TL;DR: In this paper, the key properties related to crystal-stabilized water-in-oil (W/O) emulsion formation and stability were explored, and it was shown that temperature and freeze-thaw emulsion destabilization are intimately linked with fat crystal spatial distribution.
Abstract: Products such as cosmetics, pharmaceuticals, and crude oil often exist as water-in-oil (W/O) emulsions during their processing or in final form. In many cases, their dispersed aqueous phase is encased in a crystal network and/or by interfacially-adsorbed (‘Pickering’) particles [paraffins, triacylglycerols, polymers, etc.] that promote emulsion kinetic stability by hindering droplet–droplet contact, coalescence and macroscopic phase separation. In processed foods, important questions remain regarding whether a continuous phase fat crystal network or Pickering crystal provides better stabilization. This review explores the following factors related to crystal-stabilized W/O emulsions: i) the key properties dictating fat crystal spatial distribution (at the interface or in the continuous phase); ii) how temperature and freeze–thaw emulsion destabilization are intimately linked with fat crystal spatial distribution, and; iii) why oil-soluble surfactant interactions with the continuous oil phase influence fat crystal wettability and emulsifier efficacy. It is shown that these parameters strongly govern W/O emulsion formation and stability.
TL;DR: In this article, an automated electron diffraction tomography (ADT3D) is used for structure analysis of nano-crystals with a semi-parallel beam with a diameter down to 50nm.
Abstract: Automated electron Diffraction Tomography (ADT) comprises an upcoming method for “ab intio” structure analysis of nano crystals. ADT allows fine sampling of the reciprocal space by sequential collection of electron diffraction patterns while tilting a nano crystal in fixed tilt steps around an arbitrary axis. Electron diffraction is collected in nano diffraction mode (NED) with a semi-parallel beam with a diameter down to 50 nm. For crystal tracking micro-probe STEM imaging is used. Full automation of the acquisition procedure allowed optimisation of the electron dose distribution and therefore analysis of highly beam sensitive samples. Cell parameters, space group and reflection intensities can be determined directly within a reconstructed 3d diffraction volume using a dedicated software package (ADT3D). Intensity data sets extracted from such a volume usually show a high coverage and significantly reduced dynamical effects due to “off-zone” acquisition. The use of this data for “ab initio” structure solution by direct methods implemented in standard programs for X-ray crystallography is demonstrated. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
01 Jan 2011
TL;DR: In this article, the elastic properties of twenty four hexagonal close packed (HCP) metals at room temperature are reviewed based on published values of their monocrystal elastic constants, in particular, the angular variation of the Young's Modulus (E) and the Rigidity (Shear) Modulus(G) are determined using general equations developed by Voigt [1928] and comparisons between the different metals presented graphically.
Abstract: The monocrystal elastic behaviours of twenty four hexagonal close packed (HCP) metals at room temperature are reviewed based on published values of their monocrystal elastic constants. In particular, the angular variation of the Young’s Modulus (E) and the Rigidity (Shear) Modulus (G) are determined using general equations developed by Voigt [1928] and comparisons between the different metals presented graphically. The consequences of anisotropic monocrystal behaviour on the elastic behaviour of polycrystals composed of randomly oriented grains (crystal aggregates) are explored using a three dimensional spherical analysis together with the analytical methods of Voigt [1889] and Reuss [1929], and comments made on the consequences of non-randomly oriented grains.
TL;DR: In this paper, a series of alkali and alkaline earth metal combined fluorine beryllium borates NaCaBe2B2O6F, KCaBe 2B2E6F and KSrBe 2E6E 6F were successfully synthesized through molecular engineering design and grown in crystals by spontaneous nucleation technique from self-flux systems.
Abstract: A novel series of alkali and alkaline earth metal combined fluorine beryllium borates NaCaBe2B2O6F, KCaBe2B2O6F, and KSrBe2B2O6F were successfully synthesized through molecular engineering design and grown in crystals by spontaneous nucleation technique from self-flux systems. The idea, introduction of relatively small alkali and alkaline earth metal cations and the fluorine anion, successfully resulted in the novel UV NLO crystal NaCaBe2B2O6F, the following substitution of cations directed to two centrosymmetric compounds KCaBe2B2O6F and KSrBe2B2O6F. In all of their structures, the a–b plane is the infinite lattice layer (Be3B3O6F3)∞ made up of BO3 and BeO3F anionic groups, and for the first time, it was found that the adjacent layers are connected with fluorine bridge atoms to form (Be6B6O12F3)∞ double layers, instead of oxygen bridge atoms usually occurred in other oxides. This structural characteristic is greatly beneficial to improve the layering-growth habit and eliminate polymorphism of a crystal. ...
TL;DR: This paper highlights theoretical and practical aspects of the principles that underpin acoustic analysis, then reviews exemplary papers in key application areas involving small molecular weight ligands, carbohydrates, proteins, nucleic acids, viruses, bacteria, cells and membrane interfaces.
Abstract: Since the publication of the original review of piezoelectric acoustic sensors in this series there has been a consistent, gradual expansion in the number of published papers using ‘quartz crystal microbalances’ (QCM). Between 2001 and 2009, the number of QCM publications per annum has increased from 49 to 273, with a two-fold increase in papers per annum between 2004 and 2008. Within the field, comparing the time covered by the current to the previous review, there are trends towards increasing use of QCM in the study of protein adsorption to surfaces (93% increase), homeostasis (67% increase), protein–protein interactions (40% increase) and carbohydrates (43% increase). New commercial systems have been released that are driving the uptake of the technology for characterization of binding specificities, affinities, kinetics and conformational changes associated with a molecular recognition event. This paper highlights theoretical and practical aspects of the principles that underpin acoustic analysis, then reviews exemplary papers in key application areas involving small molecular weight ligands, carbohydrates, proteins, nucleic acids, viruses, bacteria, cells and membrane interfaces.