Materials Literature
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Colossal magnetoresistance in excess of 106% has been obtained (at 110 K, H=6 T) in epitaxially grown La–Ca–Mn–O thin films. The as-deposited film exhibits a substantial magnetoresistance value of 39 000%, which is further improved by heat treatment. The magnetoresistance is found to be strongly dependent on film thic…
Pulsed laser ablation deposition was used to synthesize polycrystalline SrBi2Ta2O9 layered ferroelectric thin films on platinized silicon substrates. Top electrodes were produced by dc magnetron sputter deposition to fabricate capacitors for electrical tests. The polarization electric field hysteresis loops showed sat…
We report measurements of chain diffusion in macroscopically oriented, well-entangled lamellar block copolymers. Diffusion in the lamellar plane is proposed to occur by an ``activated reptation'' mechanism when the composition profile is roughly sinusoidal. At higher degrees of segregation a crossover to an entropical…
A parameter-free, mean-field, multi-orbital Hubbard model with nonspherical Coulomb and exchange interactions, implemented around all-electron local-density approximation (LDA) calculations, correctly predicts the band-gap energy, the absence of dimerization, and the antiferromagnetic ground state of halogen-bridged l…
A set of coupled equations of motion for the evaluation of spin dynamics in magnets is introduced. This adiabatic approach considers the orientation of the local magnetic moments to be slowly varying relative to their magnitudes. The method is implemented within the local density approximation and applied to $\ensurem…
Ab initio self-consistent field (SCF), second- and third-order Mo/ller–Plesset calculations on the charge-transfer complexes of one and two alkali atoms with oligothiophenes and oligophenylenes are reported. Complexes up to quaterthiophene and quaterphenyl with Li, Na, and Cs have been investigated. The mono-alkali co…
The computer simulation of stress relaxation in a model polymer melt is performed with a nonequilibrium molecular dynamics algorithm. The chains are freely jointed with N=30, 100, and 200 bonds and with both intra- and interchain excluded volume interactions. For N=200, the model exhibits incipient plateau behavior as…
A theory of multiphonon relaxation for electronically or vibrationally excited impurities in crystals is developed. Two alternative approaches within the static-coupling scheme are presented and their relative importance is discussed. For each approach a closed-form analytical expression for the relaxation rate is giv…
We present here an optimized united atom model that is able to reproduce properties of melts of n-alkane chains of varying molecular weights. This model differs from previous models in that the Lennard-Jones well depth for the terminal methyl group (0.2264 kcal/mol) differs from that of the methylene units (0.093 kcal…
Our environment is largely one of polymers and all polymers burn whether natural or synthetic. The issue is not whether polymers burn but rather if a given polymer has a property profile appropriate to provide for an acceptable level of risk in a given application. How we make polymers flame retardant, what flame reta…
The roots of the Hankel determinant built with the Taylor coefficients of the regularized logarithmic derivative of the eigenfunction give both the bound-state and Siegert eigenvalues (resonances) of separable quantum-mechanical systems. We obtain accurate positions and widths for the resonances of some commonly chose…
Our environment is largely one of polymers and all polymers burn whether natural or synthetic. The issue is not whether polymers burn but rather if a given polymer has a property profile appropriate to provide for an acceptable level of risk in a given application. How we make polymers flame retardant, what flame reta…
The fundamental condensed phase processes which lead to char formation during the fire-like pyrolysis of poly(vinyl alcohol), PVA, and PVA-containing maleimides were characterized using CP/MAS 13 C NMR. In addition to evidence of the well known chain-stripping elimination of H 2 O and the chain-scission reactions, whi…
The authors report an all solid state, VLSI compatible, electroluminescent device based on porous silicon with an external quantum efficiency greater than 0.1% under CW operation. The emission, which is broadband and peaks at 600 nm, is detected above a low threshold current density and voltage of 0.01 Am-2 and 2.3 V,…
Tm(3+)-doped heavy metal oxide glasses in the PbO-Bi(2)O(3)-Ga(2)O(3) system were prepared, and their emission characteristics were examined. Three emission bands at the infrared wavelength region were observed, at 1.46, 1.79, and 2.36 µm, which are associated with the (3)H(4) ? (3)F(4), (3)F(4) ? (3)H(6), and (3)H(4)…
We consider the swelling kinetics of layered structures. We focus on the case of triblock copolymer mesogels, although our results are applicable to other layered structures including clays. We assume the mesogels are swollen by a solvent that is good for the bridging block but poor for the non-bridging block. At long…
Abstract Rubbers of different kind were tested as toughening agents of poly(ethylene terephthalate) (PET), noting significant morphological and mechanical differences. In particular, good results were obtained by using an ethylene–ethyl acrylate–glycidyl methacrylate copolymer. The resulting blend evidenced good parti…
Abstract A commercial linear low density polyethylene (1‐hexene comonomer) was reacted with dicumyl peroxide at appropriate levels to initiate chain extension without crosslinking. The peroxide modification was carried out both in the presence and absence of a common hindered phenolic antioxidant. Thermal treatment of…
Abstract This article begins by briefly reviewing the more important contributions to the area of modeling heat and mass transfer, and particle growth during the polymerization of olefins on Ziegler–Natta catalysts. It is shown that these models are capable of identifying the critical areas involved in heat and mass t…
In this paper I review the ways in which the glassy state is obtained both in nature and in materials science and highlight a "new twist"--the recent recognition of polymorphism within the glassy state. The formation of glass by continuous cooling (viscous slowdown) is then examined, the strong/fragile liquids classif…