Materials Literature
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Although the frequency dependent conductivity of ion-containing glasses often displays scale invariant power law dispersion at high temperatures, the exponent increases to unity at lower temperatures. We report measurements of the conductivity of a series of alkali metaphosphate glasses including a mixed alkali compos…
Amorphous carbon (a-C) films grown by vacuum-arc deposition techniques contain substantial amounts of compressive, residual, growth stress (over 10 GPa). The magnitude of the stress can be controlled by changing the incoming energy of the ions. It is observed that stress shifts the Raman scattering feature in these fi…
We present a method for electronic structure calculations that retains all of the advantages of real space and addresses the inherent inefficiency of a regular grid, which has equal precision everywhere. The computations are carried out on a {\em regular} mesh in {\em curvilinear space}, which allows natural and effic…
The perovskite-type manganese oxide, ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ $(x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.5)$, shows a first-order phase transition from a ferromagnetic (FM) metal to antiferromagnetic (AFM) nonmetal at 140 K, which accompanies the transition to…
The ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ system with $0.2\ensuremath{\lesssim}x\ensuremath{\lesssim}0.4$ has traditionally been modeled with a ``double-exchange'' Hamiltonian in which it is assumed that the only relevant physics is the tendency of carrier hopping to line up neighboring…
For the investigation of the contribution of dislocation slip on {123} glide planes during rolling deformation of b.c.c. transition metals a Taylor type model is used. The simulations are compared to experimental observations. Since the movement of dislocations on the activated glide systems gives rise to characterist…
An unusual dodecagallium cage is isolated from the oxidation and hydrolysis of [ t Bu 2 Ga(Spy)]. The structure of 1 consists of a [ t BuGa(μ‐X)Ga t Bu]‐capped oxocube (X = O, OH). In addition 2 has been isolated. Both structures show crystallographic disorder of oxo and hydroxo ligands. H‐Spy = 2‐mercaptopyridine. eq…
The effect of nitrogen and carbon on the electronic and magnetic properties of the iron-base Fe56Cr18Ni16Mn10 3d-alloy with f.c.c. lattice (austenite) is studied by means of the magnetic resonance. It is shown that the electron state density on the Fermi surface in the nitrogen austenite is one order of magnitude high…
Abstract The investigation of thermodynamic properties and reactivity yields interesting insights into the chemistry of newly synthesized substances. With thermal analysis extensive information can be gained from small samples (often only a few milligrams). In addition, the data obtained by thermal analysis can be use…
The optical rotation of poly(propylene imine) dendrimers with 64 identical enantiomerically pure amino acid end groups tends to zero. This remarkable behavior results from the packing of the end groups in the highly dense, multiply hydrogenbonded surface, which gives rise to different frozen‐in conformations, leading…
Below 4 K the [Au(CN)2] salt of the radical cation of 1 shows superconductivity. The X-ray structure analysis reveals that this salt has a two-dimensional array of donors. The relatively large interactions between the stacks result in a closed Fermi surface.
The thermal stability of the electric field induced poled order in a new class of second-order optically nonlinear polymers, "donor-imbedded" side-chain polyimides containing no flexible connectors or tethers to the nonlinear optical (NLO) chromophore, is investigated. In these polymers, the electron-donor part of the…
We present a method for reliably determining the lowest energy structure of an atomic cluster in an arbitrary model potential. The method is based on a genetic algorithm, which operates on a population of candidate structures to produce new candidates with lower energies. Our method dramatically outperforms simulated…
A class of amphiphilic macromolecules has been synthesized by combining well-defined polystyrene (PS) with poly(propylene imine) dendrimers. Five different generations, from PS-dendr-NH(2) up to PS-dendr-(NH(2))(32), were prepared in yields of 70 to 90 percent. Dynamic light scattering, conductivity measurements, and…
The title structure, HgSeO 3 , is isomorphous with those of a series of perovskite-like MSeO 3 compounds and contains corner-sharing HgO 6 octahedra, connecting to form a three-dimensional network, and Se 4+ ions in the cavities of the structure. The octahedron is substantially distorted with Hg-O bond distances betwe…
Ceric potassium nitrate, K 2 Ce(NO 3 ) 6 , was synthesized from the dissolution in nitric acid of active hydrous ceria and potassium nitrate in stoichiometric quantities. Two forms, with hexagonal and monoclinic symmetries, have been isolated. The structures were solved by single-crystal X-ray diffraction analyses. Th…
Dephasing and transient grating experiments in the direct excitonic absorption region of GaSe at low temperatures show that a fast relaxation within the one-dimensionally disordered excitonic band results in band filling being the dominant mechanism of the optical nonlinearity. Correspondingly, we observe a blueshift…
We have performed a systematic theoretical study of the effects of variations in the direction of the incoming electron beam on low-energy electron-diffraction (LEED) intensities for the surfaces Ni{111} and p(2\ifmmode\times\else\texttimes\fi{}2)C-Ni{111}. Large intensity modulations are observed for variations of th…
Photoluminescence (PL) of porous silicon in the redband is studied at temperatures from 15 to 293 K. With increasing temperature, the PL spectrum peak redshifts and the width narrows, while the PL intensity increases until \ensuremath{\sim}70 K and then decreases slightly. At 293 K, the PL at higher emission energy de…
The near-surface regions of high-purity fused silica disks (Corning 7940) were modified by implantation with Bi2+ ions at 160 keV and at room temperature. The glasses implanted with a nominal dose of 6×1016 Bi2+ ions/cm2 at ∼5 μA/cm2 were subsequently annealed in oxidizing and inert atmospheres. The annealing temperat…