Pseudohexagonal Structures Research Articles

Raisins in a Hydrogen Pie: Ultrastable Cesium and Rubidium Polyhydrides

AbstractA new method for synthesis of metal polyhydrides via high‐pressure thermal decomposition of corresponding amidoboranes in diamond anvil cells is proposed. Within this approach, molecular semiconducting cesium (P4/nmm‐CsH7, P1‐CsH15+x) and rubidium (RbH9‐x) polyhydrides with a very high hydrogen content reaching 93 at.% are synthesized. Preservation of CsH7 at near ambient conditions, confirmed both experimentally and theoretically, represents a significant advance in the stabilization of hydrogen‐rich compounds. In addition, two crystalline modifications of RbH9‐x with pseudohexagonal and pseudotetragonal structures identified by synchrotron X‐ray diffraction, and Raman measurements are synthesized. Both phases are stable at 8–10 GPa. This is an unprecedentedly low stabilization pressure for polyhydrides. These discoveries open up possibilities for modifying existing hydrogen storage materials to increase their efficiency.

Characterization of Bambu Clay as A Precursor for The Synthesis of Zeolite for Catalytic Application

The clay in Bambu town, north-central Nigeria, has been used as a ceramic formulation for several generations without understanding its properties. In this paper, the mineralogical study of the Bambu clay sample was investigated in order to deduce its properties and its potential for technological applications. Samples of the clay were first pre-treated and subjected to elemental composition using powder diffraction, morphology, Fourier transform infrared, and area-volume-pore size analyses. The results indicated that Bambu clay can be classified as kaolinite with a Si/Al ratio of approximately 1:85. From the SEM, the particles show the presence of pseudo-hexagonal structures within the clay structure. The average crystallite size was deduced from the XRD analysis to be 43.5nm. The BET analysis reveals that the surface area of the clay was 429.70 m2g- 1, pore volume was 0.042 cm3g- 1 and the pore radius was 2.14 nm. The clay showed that the sample possessed a concentration of Bronsted acidic sites of 31.57 μmol/g and Lewis acidic sites of 34.40 μmol/g. To ascertain the clay’s viability for industrial application, the results of the analyses were compared with other clays from the literature. It can be deduced from the analyses that the Bambu clay is kaolinite, mesoporous, has a crystalline structure, a low Si/Al ratio, a higher surface area than zeolite Y, and a high concentration of Lewis acidic sites and a low concentration of Bronsted acidic sites. The clay could be a good precursor material for the synthesis of zeolite Y for catalytic applications.

QUANTITATIVE AND QUALITATIVE CHARACTERIZATION OF THE GRANULOMETRY OF AN INCEPTISOL

Granulometry is an initial factor to be considered in soil research as it plays a fundamental role in physical and chemical properties. The objective of this study was to characterize the granulometric fractions of soil, obtained using the screening and sedimentation method. The Dynamic Light Scattering (DLS), Mid-Infrared (MIR), and Scanning Electron Microscopy with Field Emission Gun (SEM-FEG) techniques were used for this purpose. The quantitative results showed that this soil presents high percentage of clay, followed by fine sand fraction, silt fraction and, finally, the coarse sand fraction. The results obtained by DLS qualify this technique as a procedure to evaluate the quality of the granulometric fractionation of the clay fraction. The MIR analyzes detected characteristic vibrational states of minerals such as kaolinite, halloysite, gibbsite, and quartz. Few works in the literature characterize the clay fraction of the soil without chemical treatment using the SEM-FEG technique. Thus, in this work, pseudo-hexagonal structures were identified, typical of the kaolinite mineral and, to a lesser extent, structures with a filamentous needle-like morphology, which can be ascribed to illite and/or halloysite, whose inorganic functional groups were identified by MIR in the clay fraction of the soil.

Characterization and Assessment of Natural Amazonian Clays for Cosmetics-Industry Applications

AbstractClays are abundant materials in the Amazon region and have been used historically by ancient Amazonian people to produce ceramic and cosmetics products. The current study aimed to evaluate the potential of four clays from the metropolitan area of Manaus, each with a different color, for cosmetics applications. Two clays were collected in the Ponta Negra region (red and gray in color) in Manaus, one in Careiro (white), and one in Itacoatiara (black). After drying in an oven for 24 h at 105°C, the four clays were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), infrared (IR) spectroscopy, thermogravimetry (TGA), differential thermal analysis (DTA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), particle-size analysis, and detection of microorganisms. The amounts of Al, Si, Cl, K, Ca, Ti, Cr, Fe, Zn, P, and S in all samples were below the limits for use in cosmetics. The main phases identified were kaolinite 1A, quartz, gibbsite, and the rare kaolinite 2M. Approximately 40 wt.% of each sample was in the < 20 μm particle-size range. Analyses by SEM revealed pseudo-hexagonal kaolinite structures with nano-islands and nanocrystallites. The low toxicity, mineralogic compositions, and particle-size findings suggest that Amazonian clays are promising for cosmetics applications.

Formation of pseudo-hexagonal pyramidal structures on (111) crystallographic surfaces of cubic PbTe crystals by ion sputtering

On the example of the PbTe compound we present the results of the study of the interplay between the crystallographic orientation of the surfaces of high reticular density and easy cleaving of the crystals of cubic symmetry and the shape of surface structures induced by prolonged ion sputtering. We found that in case of right combination of the crystallographic orientation of both the sputtering surface and the planes of high reticular density in the aggregate with easy cleaving of the crystals, the pyramidal structures of pseudo-hexagonal shape can be formed on the sputtering surface of cubic crystals. In case of PbTe these are the surfaces of (111) crystallographic orientation subject to the presence of sputter-resistant protective shields on them. When the protective shields are destroyed, the hexagonal structures are transformed into trihedral pyramids. The pseudo-hexagonal pyramidal structures are characterized by indistinct edges and terrace-shaped lateral facets, whereas the facets of the trihedral pyramids, into which they are transformed during the ion bombardment, are mirror-smooth. We prove that: (a) the maximally sharpened pseudo-hexagonal pyramids, ion-induced on PbTe (111) sputtering surfaces, are formed as a result of self-organization of the crystallographic planes of the family {0ī2}, the reticular density of which directly follows the reticular density of the plane of the sputtered surface; (b) the roughness of the lateral facets of pseudo-hexagonal pyramids, as well as the mirroring of the facets of the trihedral pyramids is due to the impact of crystallographic planes of the {100}family, which are the planes of the greatest reticular density and easiest cleaving for PbTe crystals.

Insights into the TT-Nb2O5 crystal structure behavior

The discussion about the Nb2O5 crystal structure persists nowadays, especially for the TT-phase. It has been shown that the TT-phase can accommodate defects in the crystal structure due to its opened structure and non-stoichiometry behavior. Several works suggested that the TT-phase could crystallize in monoclinic, hexagonal, pseudohexagonal, or orthorhombic structures. For this reason, this work presents insights about the TT-phase crystal structure, which presented a pseudohexagonal unit cell within a disordered orthorhombic superlattice, showing a tunnel-like structure of 4 Å along the b-axis.

An efficient hexagonal image framework using pseudo hexagonal pixel for computer vision applications

Nature-inspired computing has been a real source of motivation for the development of many meta-heuristic algorithms. The biological optic system can be patterned as a cascade of sub-filters from the photoreceptors over the ganglion cells in the fovea to some simple cells in the visual cortex. This spark has inspired many researchers to examine the biological retina in order to learn more about information processing capabilities. The photoreceptor cones and rods in the human fovea resemble hexagon more than a rectangular structure. However, the hexagonal meshes provide higher packing density, consistent neighborhood connectivity, and better angular correction compared to the rectilinear square mesh. In this paper, a novel 2-D interpolation hexagonal lattice conversion algorithm has been proposed to develop an efficient hexagonal mesh framework for computer vision applications. The proposed algorithm comprises effective pseudo-hexagonal structures which guarantee to keep align with our human visual system. It provides the hexagonal simulated images to visually verify without using any hexagonal capture or display device. The simulation results manifest that the proposed algorithm achieves a higher Peak Signal-to-Noise Ratio of 98.45 and offers a high-resolution image with a lesser mean square error of 0.59.

The Friction of Structurally Modified Isotactic Polypropylene

The purpose of studies was to analyse an impact of heterogeneous nucleation of modified isotactic polypropylene (iPP) on its tribological properties. The iPP injection molded samples, produced by mold temperature of 20 and 70 °C, were modified with compositions of two nucleating agents (NA’s), DMDBS creating α-form and mixture of pimelic acid with calcium stearate (PACS) forming β–phase of iPP, with a total content 0.2 wt.% of NA’s. A polymorphic character of iPP, with both, monoclinic (α) and pseudo-hexagonal (β) crystalline structures, depending on the NA’s ratio, was verified. The morphology observation, DSC, hardness and tribological measurements as test in reciprocating motion with “pin on flat” method, were realized, followed by microscopic observation (confocal and SEM) of the friction patch track. It was found that Shore hardness rises along with DMBDS content, independent on mold temperature. The friction coefficient (COF) depends on NA’s content and forming temperature—for upper mold temperature (70 °C), its value is higher and more divergently related to NA’s composition, what is not the case by 20 °C mold temperature. The height of friction scratches and the width of patch tracks due to its plastic deformation, as detected by confocal microscopy, are related to heterogeneous nucleation modified structure of iPP.

Polymorphism of V-amylose cocrystallized with aliphatic diols

Chain-folded lamellar crystalline complexes of amylose with aliphatic diols were prepared and characterized by transmission electron microscopy as well as electron and X-ray diffraction. Four allomorphs were identified, depending on the complexing diol and crystallization conditions, that consisted of orthorhombic lattices of antiparallel 6- or 7-fold amylose single helices. Straight-chain n-diols (ethane-1,2-diol, butane-1,4-diol, hexane-1,6-diol) yielded 6-fold helical complexes regardless the length of the linear chain, whereas a bulkier branched diol (2-methylpentane-2,4-diol) induced the formation of 7-fold helices. Butane-1,3-diol, that contains a straight carbon chain with one end and one side hydroxyl group, induced both 6- and 7-fold helical conformations depending on the crystallization conditions. When a diol induced more than one allomorph, an adequate control of its concentration and crystallization temperature allowed targeting a specific crystalline form. Upon drying, all allomorphs were converted into more compact pseudo-hexagonal structures. The dried form of a given complex generally retained the same helical conformation as the hydrated one.

Morphologies of Primary Cu6Sn5and Ag3Sn Intermetallics in Sn–Ag–Cu Solder Balls

This article focuses on the morphologies of primary Cu6Sn5 and Ag3Sn intermetallics in small Sn–Ag–Cu (O $270~\mu \text{m}$ ) solder balls. The Cu6Sn5 phase showed a large variety of different shapes and sizes, ranging from facetted hexagonal rods, to partly facetted splitting crystals and parallel growing branches, to dendritic crystals without facets. The results of electron backscatter diffraction (EBSD) measurements confirm [0001] as the major growth direction and the { $10\bar {1}0$ } planes as facets of the hexagonal rods. The formation of crystals splitting parallel to the { $10\bar {1}0$ } planes may be caused by a slight deviation of the major growth direction toward $\langle 2\bar {1}\bar {1} 0\rangle $ . Primary Ag3Sn intermetallics showed less morphology variations and solidified as typical plate structures with a planar and an irregular side. Sixfold star-shaped formations of multiple plates arranged around a common center have been investigated by EBSD. All plates appear to have the same hexagonal orientation and possible growth directions are parallel to the { $10\bar {1}0$ } planes. However, these pseudohexagonal structures showed color differences between plates of different growth directions, if investigated with polarized light microscopy. Those orientation differences were not detectable by EBSD. Possible interpretations are discussed on the basis of the orthorhombic distorted lattice and by possible twinning mechanisms.

Discovery of hierarchical superstructures in block copolymers by integrating different liquid crystalline interactions.

Hierarchically assembled superstructures of block copolymers are discovered by introduction of the competition of anisotropy attributed from liquid crystalline ordering and nano-phase separation. When the two prototypical fields of liquid crystals (LCs), smectics (S) and nematics (N), are adjoined within the framework of diblock copolymers (S-N) in a variety of precisely tuned compositions, a novel class of superlattices with an interdigitated array of smectic layers between the nearest lamellae or cylinders are observed. This generates unconventional nano-phase separated orthorhombic (Lo) and pseudo-hexagonal (Ho) structures, where the stretched N tethers, projected regularly from the S layers, could transfer the local organization and guide the correlated assembly. This type of superstructure is highly frustrated in reversed cylindrical morphology and absent in S-coil diblock copolymers. The collective interplay of the S and N interactions with nano-phase separation induces the formation of the final complex yet equilibrium structures, providing unprecedented opportunities towards exquisite structural diversity.

Axial Ligand Effects on the Structures of Self-Assembled Gallium-Porphyrin Monolayers on Highly Oriented Pyrolytic Graphite.

Monolayers of five-coordinate gallium octaethylporphyrin complexes (Ga(OEP)X; X = Cl, Br, I, O3SCF3, CCPh) on highly oriented pyrolytic graphite were studied at the solid-liquid (1-phenyloctane) interface using scanning tunneling microscopy (STM) to probe the dependence of their properties on the nature of the axial X ligand. Density functional theory calculations of the gas-phase structures of the free molecules reveal that the gallium atom is positioned above the plane of the porphyrin macrocycle, with this pyramidal distortion increasing in magnitude according to X = O3SCF3 (displacement = 0.35 Å) < Cl, Br, I (∼0.47 Å) < CCPh (0.54 Å). All compounds exhibit pseudohexagonal close-packed structures in which the porphyrin is oriented coplanar with the surface and the axial ligand is oriented perpendicular to it, and with unit-cell parameters that are within experimental error of each other (a, b = 1.34 (3)-1.39 (2) nm, Γ = 66 (2)-68 (1)°). In contrast to these close similarities, the stabilities of the monolayers are sensitive to the nature of the axial ligand: the monolayers of Ga(OEP)(O3SCF3) and Ga(OEP)(CCPh) exhibit damage during the STM experiment upon repeated scanning and upon toggling the sign of the bias potential, but monolayers of Ga(OEP)Cl, Ga(OEP)Br, and Ga(OEP)I do not. A second important ligand-influenced property is that Ga(OEP)I forms bilayer structures, whereas the other Ga(OEP)X compounds form monolayers exclusively under identical conditions. The top layer of the Ga(OEP)I bilayer is oriented with the iodo ligand directed away from the surface, like the bottom layer, but the molecules pack in a square, lower-density geometry. The comparatively large polarizability of the iodo ligand is suggested to be important in stabilizing the bilayer structure.

Efficiency enhancement in solution processed small-molecule based organic solar cells utilizing various phthalocyanine–tetrabenzoporphyrin hybrid macrocycles

A study on efficiency enhancement in solution processed small-molecule based organic solar cells (OSCs) utilizing various phthalocyanine–tetrabenzoporphyrin hybrid macrocycles is reported. By replacement of aza links at meso position by methine groups, the optical absorption at B band of porphyrinoid complexes is improved, the energy bandgap is enlarged, and stacking of the discotic molecules is probably changed from pseudohexagonal structures to 2-D rectangular lattices. Results from molecular orbital (MO) calculation by using B3LYP-optimized geometries calculated with 6-31G(d) indicate that the intensification of optical absorption and the modification of electronic band structure is mainly due to the difference of MO coefficients at meso positions, resulting in a marked lifting of the degeneracy of the MOs derived from highest occupied molecular orbitals and/or lowest unoccupied molecular orbitals. By controlling the numbers of aza links at meso position, active layer thickness and nanoscale phase separation, the external quantum efficiency at B band and power conversion efficiency of OSCs utilizing phthalocyanine–tetrabenzoporphyrin hybrid macrocycles is improved to 53% and 5.3%, respectively.

Nanostructured Nb2O5 Polymorphs by Electrospinning for Rechargeable Lithium Batteries

Polymorphs of 1D nanostructures of niobium pentoxide (Nb2O5) are synthesized by electrospinning. Pseudohexagonal (H−Nb2O5), orthorhombic (O−Nb2O5), and monoclinic (M−Nb2O5) structures of Nb2O5 are developed in this study by appropriate heat treatment. Morphological, structural, and electrochemical properties of these nanofibrous polymorphs are studied in detail. The H− and O− phases maintain the usual fibrous morphology, whereas the M− phase adopted a distorted nugget structure. These phases are evaluated for their application as cathode for lithium batteries. The M−Nb2O5 exhibits the highest capacity and better capacity retention compared to the other phases. The M−Nb2O5 delivers a specific capacity of 242(±3) and 218(±3) mAhg−1, cycled at a current of 50 mAg−1 in the voltage range, 1.0−2.6 V versus Li/Li+ at the end of second and 25th cycle, respectively. The electrospun M−Nb2O5 nuggets-based battery performs better than its particle/nanofiber counterpart and could be a cathode material of choice for 2 ...

Preparation and Characterization of MM’Si4N6C Ceramics

The preparation of high temperature ceramics simultaneously containing silicon, nitrogen and carbon has only relatively recently become an area of interest for inorganic crystal chemists, and the recent discovery of a new series of carbonitrides with the general formula MM’Si4N6C is of interest because of the good high temperature properties they appear to display. On the one hand, M and M’ can be the same trivalent metal - either rare earth or yttrium; in this case, the resulting compounds display orthorhombic (pseudo-hexagonal) structures. Alternatively the metals may be a mix of di- (Ca,Sr, Ba) and tri-valent (Y,Ln) cations, in which case the carbon is replaced by nitrogen, and the overall symmetry is hexagonal. Other quaternary nitrides of a similar type can be produced if the two metal cations remain trivalent and one of the silicon atoms is replaced by aluminium. The present study describes the preparation of powder samples of Y2Si4N6C and LaYSi4N6C starting from YH2, La, Si3N4 and carbon precursors, and summarises attempts to achieve a dense product by hot-pressing at 1700-1800oC. Some preliminary mechanical property measurements are included.

Characterization of lamellar phases fabricated from Brij-30/water/1-butyl-3-methylimidazolium salts ternary systems by small-angle X-ray scattering

Abstract The lamellar liquid crystalline phases composed of either imidazolium salt, the hydrophilic 1-butyl-3-methylimidazolium tetrafluoroborate (bmim-BF 4 ) or the hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate (bmim-PF 6 ), in aqueous solution of Brij-30 (tetraethylene glycol lauryl ether, C 12 E 4 ) have been assembled at a constant temperature ( T = 25 °C). Their elaborate structures such as the distribution of hydrophobic or hydrophilic parts of surfactant bilayer and water are revealed quantitatively by several structural parameters derived from small-angle X-ray scattering (SAXS) measurements. The effects of system composition and temperature on the lamellae are discussed with comparison to the corresponding Brij-30/water binary mixture. It concludes that the bmim-PF 6 molecules tend to situate at the interface between polar and apolar regions and therefore cause a decrease of combined water amount around EO blocks. Bmim-BF 4 molecules, however, like to locate themselves at water interlayers as well as in the polar domains. In addition, the pseudo-hexagonal columnar structures or micelles observed respectively at low or high temperatures are analyzed by SAXS and differential scanning calorimetry (DSC) methods.

Synthesis of submicron gibbsite platelets by organic-free hydrothermal crystallization process

An environmental benign organic-free hydrothermal crystallization process is applied to synthesis of gibbsite platelets, which are well-defined, regularly shaped and monodispersed pseudohexagonal submicron structures with an average width of 0.6–0.8 μm and a thickness of 40 nm. The structure and morphology of resulting solids depend to a great extent on the pH of media for hydrothermal crystallization. An acidic condition of pH 5.0 is favorable for the growth of submicron gibbsite platelets with high purity, whereas alkaline condition results in boehmite and neutral medium is unfavorable for crystal growth in this study. The properties of materials obtained by hydrothermal crystallization have been investigated by SEM, XRD, 27Al MAS-NMR, XPS, and solid UV-vis spectroscopy.

High‐density polyethylene layered silicate nanocomposites: Effect of mechanical stretching on the crystal‐to‐crystal transformations, morphology, and extent of exfoliation

AbstractHigh‐density polyethylene/clay nanocomposites were elongated until breakage to investigate the effect of the mechanical stretching on the crystal‐to‐crystal transformations and their morphology. Crystalline transformations of the polymer matrix were studied via Fourier transform infrared spectroscopy, differential scanning calorimetry, and X‐ray diffraction measurements. It was concluded that the stress‐induced crystal‐to‐crystal transformations from orthorhombic structures to monoclinic and pseudohexagonal structures as well as the back‐transformation during relaxation were hindered by the presence of the clay. X‐ray diffraction studies on stretched samples showed that the mechanical stretching led from an intercalated structure to an almost exfoliated structure. These findings agreed with scanning electron micrographs, in which the beneficial effect of stretching on the exfoliation of the clay was evident. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 914–924, 2006

2D Spatially Periodic Architectures via the Drying of 1D Holographically Photopatterned Polymer Solutions

We demonstrate an efficient and versatile method for selectively generating 1D and 2D periodic polymer structures in the submicron to tens of micron range by the directed drying of 1D photopatterned polymer solutions. Ultraviolet (UV) holographic lithography (Xia et al. Chem. Rev. 1999, 99, 1823-1848) is initially used to create 1D periodic cross-link and density variations in the polymer/volatile solvent solutions. These variations act as anisotropic barriers (walls) that direct the subsequent solvent evaporation process. Somewhat akin to directional drying (Allain and Limat Phys. Rev. Lett. 1995, 74, 2981-2984) and directional solidification (Pelc, P. Dynamics of Curved Fronts; Academic Press: San Diego, CA, 1988) experiments, the drying exhibits channel-like interface propagation behavior. The combination of the instabilities and minimization of the interface area during drying can be effectively used to produce larger scale 2D pseudohexagonal polymer-strut structures, or by the addition of a monomeric component to the polymer solution, the instabilities can be suppressed, resulting in the formation of 1D linear gratings.

π‐conjugated columnar polyacetylenes prepared with Rh complex catalysts

AbstractHighly stereospecific polymerization of monosubstituted acetylenes was carried out using the Rh complex, [Rh(norbornadiene)Cl]2 catalysts. The resulting polyacetylenes were characterized in detail by 1HNMR, ESR, laser Raman, diffuse reflective UV, and wide angle X‐ray diffraction methods. The data showed that the Rh complex were the preferred catalyst to selectively yield the corresponding cis‐transoid polymers even at room temperature when alcohol, triethylamine or water was used as the polymerization solvent. Additionally, the resulting cis polyacetylenes were found to have a helical form whose polymer is amorphous or composed of pseudohexagonal structures called π‐conjugated columnar as self‐assembly or super structure. Further compression of the amorphous cis polymers resulted in cis to trans isomerization at room temperature under vacuum, breaking rotationally the cis C=C bonds giving π‐radicals called solitons as the origin of a polymer magnet. On the other hand, the π‐conjugated columnar was also found to show an extremely longer wavelength absorption compared with that of the amorphous one, although the absorption maximum was shifted to a shorter wavelength when the columnar was destroyed by the compression. Therefore, the formation of the π‐conjugated columnar can be considered as a new and quite useful control method concerning color of such conjugated polymers, i.e., a new concept concerning the color of conjugated polymers.