Materials Literature
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One of the important problems of high-temperature superconductivity is to understand and ultimately to control fluxoid motion. We present the results of a new technique for measuring the pressure dependence of the transition to superconductivity in a diamond anvil cell. By measuring the third harmonic of the {\it ac}…
The H-T phase diagram of CuGeO$_3$ has been determined, for different values of the hydrostatic pressure, utilizing optical absorption spectroscopy on the Cu$^{2+}$ d-d transitions. It is shown that the intensity of the related zero phonon line transition is very sensitive to the local environment of Cu$^{2+}$, allowi…
The oxidation behavior of porous silicon (PS) has been found to be related to illumination during etching. The autocatalytic oxidation behavior at room temperature arises from the unrelaxed surface induced by the preparation under illumination and can be removed using thermal treatment in a nitrogen atmosphere. The ef…
We have studied the kinetics of phase separation in a colloid-polymer mixture. The evolution of initially homogeneous samples as they separate into coexisting colloidal gas, liquid, and crystal phases was investigated by time-lapse video recording. Distinct kinetic regimes were found, the existence and character of wh…
Neutron powder diffraction experiments on layered manganites ${\mathrm{La}}_{2\ensuremath{-}2x}{\mathrm{Sr}}_{1+2x}{\mathrm{Mn}}_{2}{\mathrm{O}}_{7}\phantom{\rule{0ex}{0ex}}(0.32\ensuremath{\le}x\ensuremath{\le}0.40)$ show that coherent lattice anomalies observed at the Curie temperature (lattice parameters, Mn-O bond…
A polarization-insensitive, electrically tunable Fabry-Perot filter (FP) with a nematic liquid crystal (NLC) is demonstrated in an axially symmetrical configuration. Due to the axial symmetry, the wavelength-selection property of the FP filter is completely independent of the polarization state of the input beam in th…
A diamond detector type 60003 (PTW Freiburg) was examined for the purpose of dosimetry with 4-20 MeV electron beams and 4-25 MV photon beams. Results were compared with those obtained by using a Markus chamber for electron beams and an ionization chamber for photon beams. Dose distributions were measured in a water ph…
We have synthesized nanoparticles of ZnS doped with Mn for potential use as cathodoluminescent phosphors in field-emission displays (FEDs). We show that the cathodoluminescent efficiency of particles ⩽100 nm in diameter is within 40% of that of a commercial (micron-sized) phosphor when the electron-beam energy ranges…
A microscopic model for polarization fatigue in ferroelectric perovskites based on dipolar defects formed by the combination of oxygen vacancies and impurity metal ions is presented. The binding energy of an oxygen vacancy to a Pt impurity in $\mathrm{PbTiO}{}_{3}$ is calculated to be $\ensuremath{\sim}2.9\mathrm{eV}$…
Measurements of photoluminescence (PL) from composites of silica nanoparticles (the primary particle size 7 and 15 nm) as a function of heat treatment temperature show that the PL results from hydrogen-related species and thermally produced structural defects. The PL was induced by an ArF or Nd:YAG (yttrium–aluminum–g…
A simple model based on atom-atom potential has been used to calculate various bulk, structural and thermodynamic properties of pure C_{60} solid by including implicit anharmonicity. The pressure and temperature dependent properties such as bulk modulus, lattice and orientational structure, thermal expansion, phonon f…
Electron dynamics in the bulk and at the surface of solid materials are well known to play a key role in a variety of physical and chemical phenomena. In this article we describe the main aspects of the interaction of low-energy electrons with solids, and report extensive calculations of inelastic lifetimes of both lo…
The coefficient of diffusion of hydrogen in crystalline silicon is calculated using tight-binding molecular dynamics. Our results are in good quantitative agreement with an earlier study by Panzarini and Colombo [Phys. Rev. Lett. 73, 1636 (1994)]. However, while our calculations indicate that long jumps dominate over…
High-energy (>1.6 MeV) electrons create acceptors and donors in single-crystal ZnO. Greater damage is observed for irradiation in the [0001] direction (Zn face) than in the [0001̄] direction (O face). The major annealing stage occurs at about 300–325 °C, and is much sharper for defects produced by Zn-face irrad…
We report on the investigation of ferroelectricity in thin tetragonal single-crystalline perovskite films of Pb(Zr0.2Ti0.8)O3 grown by off-axis rf magnetron sputtering. The local ferroelectric properties of atomically smooth films, with thicknesses ranging from a few unit cells to 800 Å, were measured using a combinat…
We observe that field emitters made from carbon nanotubes exhibit excellent macroscopic emission properties; they can operate at a very large current density, as high as 4 A/cm2. At electric fields as low as 4–7 V/μm, they emit technologically useful current densities of 10 mA/cm2. We show that the emission originates…
By differential scanning calorimetry (DSC), the thermal behavior of polytetrafluoroethylene (PTFE) and random fluorinated copolymers of tetrafluoroethylene-containing hexafluoropropylene (FEP copolymers) or perfluoroalkylvinylether (PFA copolymers) as comonomers was investigated. Rapid-melt crystallization was employe…
Soluble polyimides were synthesized and characterized from two diamines and four dianhydrides by the two- and the one-step method. Most of the polyimides could be soluble by one-step method except α,α′-bis(4-aminophenyl)-1,4-diisopropyl benzene/3,3′,4,4′-benzophenonetetracarboxylic dianhydride system in limited organi…
Vulcanization of carboxylated nitrile rubber (XNBR) with different vulcanizing agents (i.e., zinc peroxide, sulphur, and a zinc peroxide–sulphur mixed system) was studied. Properties of the vulcanized compounds depend on the type of crosslinking produced (i.e., ionic or covalent) rather than the crosslinking density.…
The mechanical properties (tensile, flexural modulus, and impact strength) and the flame retardance of glass fiber-reinforced novolac-type phenolic resin modified with polyamide (PA-6, PA-66) were investigated. Results show that polyamide improves the mechanical properties of composites, especially for the impact stre…