Deformation Induced Micro-Twins in CdTe?

Room- and high-temperature micro-indentation experiments have been performed to answer the question if, concerning a material with very low stacking-fault energy like CdTe, deformation induced twinning occurs in these substances during or shortly after growth. Micro-twins appear in consequence of room-temperature deformation only, whereas microindentation at 565°C does not produce any twins, but leads to widely expanded dislocation glide-figures, due to dislocation climbing and/or cross-gliding.     

Behavior of poly(ε-caprolactone)-based diblock copolymers in a bulk state and in solution

Abstract

A series of amphiphilic MOPEO-b-PCL copolymers (DBCs), based on biocompatible methoxypoly(ethylene oxide) with M_n=4.5?kDa and poly(ε-caprolactone) of a variable chain length, was synthesized by an anionic ring-opening block copolymerization. The structural investigations, performed by DSC and WAXS methods, revealed the microphase separation in DBC bulk structure and the existence of separate amorphous regions and microcrystalline domains of MOPEO and PCL blocks. Spectrophotometry and SLS were used to study the self-assembling of DBC macromolecules in selective dioxane/aqueous solution and to determine the main micellization parameters (CMC and -ΔG°). The DBC micelles morphology and their specific aggregation in mixed solvent were shown.     

Properties of Some Polarized Chromophores in Polyvinylpyrrolidone

Poor miscibility of highly polarized chromophores to polymer matrices is a crucial issue for EO polymer development. By using poly(N-vinylpyrrolidone) (PVP) as a matrix polymer, we were able to prepare the uniform film containing ammonium-borate type zwitterions or Disperse Red 1 (DR1). For zwitterions, corona poling was unsuccessful probably because of hygroscopic property of PVP and/or strong intermolecular interaction to form the antiparallel dimers. For DR1, we found apparent color change originated from the H-aggregate formation assisted by moisture, which is usable to detect humidity. On the other hand, a passivation layer is necessary to use PVP for the EO applications.     

Threshold switching in niobate glass — thick-film devices

Thick-film, niobate-glass threshold switches have been made in reducing gas atmospheres at high temperatures (1100–1400°C) using SiO₂ and B₂O₃ as glass formers. Their temperature characteristics are far superior to those of similar vanadate switches previously reported [1,2], and they are stable at low ON currents (< mA) if they are protected from atmospheric oxidation. They do not require forming.The process consists in pre-firing the printed, powdered glass in air and then reducing in argon/hydrogen gas. While the reducing conditions are not critical and virtually full reduction to tetragonal NbO₂ occurs, the pre-firing conditions in air are critical if high-resistance devices are to be obtained. Many devices can be made on a single alumina chip and the results of a statistical analysis are given.The electrical characteristics — measured, chiefly, using a double-pulse technique to examine the change in delay time with pulse separation, ON current, pulse width, etc. — are similar to those previously reported for the vanadate switches [2]. These measurements, together with the results of a microscope and electron-microprobe examination, indicate that a thermal mechanism of switching with filament or channel formation is the most likely. A steady-state computer simulation based on the thermal model indicates the temperatures to be expected during switching, and these are calculated to be less than the NbO₂ semiconductor-metal transition temperature of roughly 800°C, for all the cases examined.     

Distribution of Iron Atoms in Nonequivalent Crystallographic Sites of Fe7C3 Carbide in Core–Shell Nanostructures

Crystallography Reports - The structure and magnetic properties of iron carbide nanoparticles encapsulated into carbon shells, obtained as a result of ferrocene transformations at a pressure of 8...     

Crystallization kinetics in Se–Te glassy system

Differential scanning calorimetry measurements were used to study crystallization in the Se_yTe_(1 ? y) glassy system under non-isothermal conditions. The examined compositions were y = 0.1, 0.2 and 0.3. The crystallization kinetics was described in terms of the Johnson–Mehl–Avrami nucleation–growth model. It was found that with the addition of tellurium into the selenium matrix the apparent activation energy of the crystallization process monotonically increases and, more importantly, the parameter of the JMA model m decreases. This change in the crystallization mechanism was interpreted as a gradual crossover from surface to bulk process. Both processes are competitive and proceed simultaneously in glasses with low tellurium content, while in the case of increased Te content the surface crystallization mechanism recedes. The transition between mechanisms was discussed in terms of changes in molecular structure of the material.     

Trapping organic molecules in sol–gel aluminosilicate matrices

Inorganic materials may be tailored to obtain specific pore size distributions and surface structures. In this work we present the synthesis of faujasite type amorphous aluminosilicate matrices by the sol–gel process. One of the preparations included the use of mesitylene as a template to create additional porosity. The powders were used to encapsulate the dyes methylene blue (MB) and malachite green (MG). Several analysis were performed, including X-ray diffraction (XRD), small angle X-ray scattering (SAXS), nitrogen adsorption/desorption, scanning electron microscopy (SEM), UV–vis, and diffuse reflectance spectroscopy. According to the results, MB and MG were effectively trapped in the aluminosilicate matrix.     

Quo vadis natural fibres in 21st century?

ABSTRACT

The global production of natural fibres is evaluated at the level 35–40 million tons/year. It is expected that the global megatrends in population growth, prosperity growth, climate change and limited cotton supply, increase in fiber consumption will lead to a demand overhang for other cellulosic fibers, including new lately discovered natural fibres. There is fierce competition between natural and man-made fibres and also both types co-exist on markets mainly in terms of quality, sustainability and physiological influence in human body. The paper focuses on the novel trends in natural fibres processing and utilization, recently explored natural fibres and their potential.     

Diffusion of ethanol–carbon dioxide in silica gel

Extraction of a primary solvent with liquid or supercritical carbon dioxide is the most difficult to control stage in low-temperature silica aerogel production. Diffusion of primary ethanol through alcogel structure to surrounding CO₂ was investigated in carefully controlled experiments with cylindrical alcogel samples. Changes of the alcohol concentration in carbon dioxide leaving the autoclave were followed with on-line chromatograph analysis and experiments were repeated for temperatures around the critical point of carbon dioxide. On the basis of the concentration histories during the drying, the temperature dependence of diffusion coefficient in the ethanol–CO₂ mixture inside the silica gel at constant pressure was identified.     

Composition–structure–property relationships in boroaluminosilicate glasses

The complicated structural speciation in boroaluminosilicate glasses leads to a mixed network former effect yielding nonlinear variation in many macroscopic properties as a function of chemical composition. Here we study the composition–structure–property relationships in a series of sodium boroaluminosilicate glasses from peralkaline to peraluminous compositions by substituting Al₂O₃ for SiO₂. Our results reveal a pronounced change in all the measured physical properties (density, elastic moduli, hardness, glass transition temperature, and liquid fragility) around [Al₂O₃]–[Na₂O] = 0. The structural origin of this change is elucidated through nuclear magnetic resonance analyses and topological considerations. Furthermore, we find that addition of 1 mol% Fe₂O₃ exerts a complicated impact on the measured properties.     

Drift mobilities in amorphous AsSeTe

The electron and hole drift mobilities in As_xSe_100?x?yTe_y (0 ? x ? 7.1, 0 ? y ? 20.9 at.%) evaporated thin amorphous films and their temperature dependence were measured by means of the time-of-flight technique. The electron mobility decreases with increasing As content, while the hole mobility decreases upon addition of 6.4 at.% Te, then remains almost similar on further addition of Te. These effects of As and Te on the drift mobilities of carriers were shown to be independent of each other.     

Recent advances in III–V compounds on silicon

The performance of photonic and electronic devices fabricated with III–V compounds on silicon substrate has advanced to the degree that this technology may be considered for device applications. In this paper, the recent advances on the growth, characterization, and applications of III–V compounds on Si substrates using low pressure metalorganic chemical vapor deposition growth technique are presented.     

Peculiarities of pendellösung fringes in quartz monocrystals

The scattering of X-rays in quartz monocrystals has been investigated. It has been discovered experimentally, that even for the thick quartz crystals, for which μt = 5, pendular bands can be obtained. The appearance of pendular bands depending on the crystal thickness, the reflecting plane families and the reflection order, was investigated as well.