Materials Literature
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The effect of externally applied stresses of eg and t2g symmetry on the cubic Eg(X)eg Jahn-Teller (JT) system Y2+ in SrCl2 is studied. Coupling constants were obtained with the aid of EPR and by relying on a Ham-type cluster JT Hamiltonian, in conjunction with a random strain distribution. This is established from a c…
An ENDOR investigation has confirmed that the OK1 centre is a low-symmetry ( sigma h ) centre, incorporating a single nitrogen atom. The 14 N hyperfine and quadrupole coupling matrices have been determined by fitting the data to an exact solution of the energy matrix. Using this and other new experimental data the aut…
The angular dependences of the time and frequency parameters of a single-crystal collective nuclear resonance were studied in a unified series of measurements and compared with the resonance parameters of an isolated nucleus. It was shown that, when approaching the Bragg angle ( theta B ), the coherent character of ga…
We report measurements of the impurity-concentration and crystal-size dependences of the threshold field ${E}_{T}$ for charge-density-wave (CDW) depinning in ${\mathrm{NbSe}}_{3}$. These measurements establish that CDW's in Ta-doped ${\mathrm{NbSe}}_{3}$ are weakly pinned. Size dependence of ${E}_{T}$ occurs when the…
L-arginine phosphate monohydrate (LAP) and deuterated LAP (DLAP) are new organic nonlinear optical materials useful for higher harmonics of radiation from high-power lasers. We measured the bulk laser damage threshold of these crystals using light from a 1.05 μm laser with 1 and 25 ns pulse widths and 0.53 μm laser li…
Abstract The crystallography and morphology of barium sulphate crystals produced by a range of desmid species have been examined by electron microscopy and electron diffraction. The morphology of the BaSO4 crystals varies between desmid species and water chemistry. Tabular, rhombic crystals are commonly produced by Cl…
Two orthogonally aligned liquid crystal lenses with spherical Fresnel zone plate electrode configurations have been demonstrated to focus an unpolarised broadband object with resulting good quality images. Switch on times of 15ms are reported along with modulation depths of 91.5%.
The sphinx is a non-periodic tiling of the plane made of one type of tile. In order to characterise the type of order found in this tiling, the computation of its diffraction spectrum is considered. The spectrum contains a discrete component, with Bragg peaks located at the vertices of triangular lattices with lattice…
Abstract The thermolysis of vinyl methylterephthalate has been studied as a model of poly(ethylene terephthalate) (PET) thermolysis. Based upon this reaction, a potential mechanism for PET flame retardation is proposed. The assumption is made, based upon firm experimental evidence, that the initial step in PET degrada…
The dynamical behaviour of the alkyl chains in dicopper tetrapalmitate is investigated in the columnar liquid crystal phase, using incoherent quasielastic neutron scattering by several selectively deuterated derivatives. A mathematical model is developed for the evaluation of the scattering function which yields the f…
Lead monohydrogen phosphate (PbHPO 4 ) undergoes a ferroelectric phase transition at T c =310 K at atmospheric pressure. T c falls to room temperature at a pressure of about 0.125 GPa. The crystal structure of PbHPO 4 has been determined by X-ray diffraction at 2.0 and 2.3 GPa and the lattice parameters have been meas…
For the crystallization of proteins under microgravity conditions, a Chinese re‐entry system was used, in which 101 experiments of 25 different biological macromolecules were accommodated. From the results obtained we conclude that under microgravity conditions crystal growth can only be expected under those crystalli…
We present experimental evidence of the smectic-A (${S}_{A}$) phase in colloidal solutions of tobacco mosaic virus. The smectic-A phase is determined by the observation of a layered structure along the virus alignment direction and a liquidlike order within layers. In our samples, we also observed the characteristic $…
We have measured Raman spectra of diamond films prepared by a hot-filament method and found that diamond layers on Si substrates are under compressive strain. The degree of the strain is found to increase with increasing nondiamond component in the diamond films. It is shown that Raman spectroscopy is a powerful metho…
For pt.I see ibid., vol.21, p.1423 (1988). Several transition-metal compounds show a transition from the low-spin to the high-spin electronic state with increasing temperature. The cooperative nature of the transition in the solid state is attributed to the elastic interaction between the spin-changing ions as a resul…
The temperature dependence of x-ray peak intensities of icosahedral AlCuFe is studied in detail. Above 670 \ifmmode^\circ\else\textdegree\fi{}C, measurements of the Debye-Waller factor suggest the presence of dynamical phasons. Softening of the phason modes drives a structural transition at \ensuremath{\sim}670 \ifmmo…
We report light-scattering measurements of powder diffraction patterns of crystals of essentially hard colloidal spheres. These are consistent with structures formed by stacking close-packed planes of particles in a sequence of permitted lateral positions, A,B,C, which shows a high degree of randomness. Crystals grown…
For single-phase polycrystalline materials the relation is discussed between the elastic strain ϵ(ψ, φ) obtained from X-ray diffraction experiments and the polynomial expansion of the stress components σφ(σ) and σφ+90(z) with respect to the distance z from the external surface of the specimen. A universal plot is prop…
The charge-transfer (CT) interactions in electroactive polymeric complexes formed by nonconjugated polymers: poly-2-vinylpyridine, poly-4-vinylpyridine, and various halobenzoquinone electron acceptors such as: o-chloranil, p-chloranil, o-bromanil, and p-fluoranil have been investigated by means of x-ray photoelectron…
The fully oxidized form of polyaniline, pernigraniline, is studied in the framework of a Su-Schrieffer-Heeger-like Hamiltonian. The protonation process of a long oligomer is investigated. Protonation is modeled by a change in site energies around the protonated site. The results of the calculataions indicate that a ph…