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We have performed extensive self-consistent total energy calculations for PbTiO3 and BaTiO3 in order to better understand the origin of the ferroelectric instability in perovskites and the reasons for different ferroelectric behavior in the two materials. Physically reasonable ferroelectric instabilities are found for…
The kinetics of the L-lactide bulk polymerization was studied using tin(II) bis(2-ethylhexanoate) and zinc bis(2,2-dimethyl-3,5-heptanedionato-O,O'). Up to 80% conversion, the rate of polymerization using tin(II) bis(2-ethylhexanoate) is higher than that with the zinc-containing catalyst, while at conversions beyond 8…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAll-solid-state sodium-selective electrode based on a calixarene ionophore in a poly(vinyl chloride) membrane with a polypyrrole solid contactAodhmar. Cadogan, Zhiqiang. Gao, Andrzej. Lewenstam, Ari. Ivaska, and Dermot. DiamondCite this: Anal. Chem. 1992, 64, 21, 2496–2501Pu…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTThe selective functionalization of saturated hydrocarbons: Gif chemistryDerek H. R. Barton and Dario DollerCite this: Acc. Chem. Res. 1992, 25, 11, 504–512Publication Date (Print):November 1, 1992Publication History Published online1 May 2002Published inissue 1 November 1992…
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPoly(ethylene oxide)-silicate intercalation materialsPilar Aranda and Eduardo Ruiz-HitzkyCite this: Chem. Mater. 1992, 4, 6, 1395–1403Publication Date (Print):November 1, 1992Publication History Published online1 May 2002Published inissue 1 November 1992https://pubs.acs.org/…
Contrary to common textbook statements, the macroscopic electric polarization of a crystal cannot be unambiguously defined as the dipole of a unit cell. The only measurable quantities are either derivatives of the polarization (dielectric susceptibility, Born effective charges, piezoelectricity, pyroelectricity) or fi…
The development of recording media based on molecular spin‐transition (ST) materials is discussed and applications demonstrated for the first time. The figure shows a compound which exhibits an ST and which is based on Fe II and 1,2,4‐triazole units. The central Fe II ion undergoes an ST at around 210 K which is accom…
Description of the spectrometer x-ray source monochromator electron lens hemispherical analyser multichannel detector sample analysis chamber charge compensation performance on conducting samples performance on insulating samples performance on testing of the spectrometer experimental protocol sample mounting data acq…
Elastic scattering of polarized electrons from unpolarized Hg, Tl, and Pb atoms has been studied at energies ranging from 0.3 to 2.0 eV and scattering angles ranging from 30' to 125'. The experimental data of the Sherman function S are compared with two calculations in which the target configuration is accounted for i…
The optical absorption, site selective excitation and luminescence spectra of the trivalent praseodymium ion in three rare earth gallium garnet matrices, RE 3 Ga 5 O 12 (REGG; RE=Y, Gd, and Pr) were detected at 4, 77 and 300 K. The 4f 2 energy level schemes comprising 56 to 68 crystal field (CF) sublevels were simulat…
Ultrathin films of vanadyl phthalocyanine (VOPc) have been grown on hydrogen-terminated Si(111) surfaces by molecular beam epitaxy. Epitaxial growth was examined on the two types of substrates. Reflection high energy electron diffraction studies have revealed that VOPc molecules form commensurate lattices [−3[3 1]4],…
A sudden shift from a bidimensional to a three-dimensional growth mode is observed when InAs is deposited by molecular-beam epitaxy on a pseudomorphic buffer layer grown on GaAs. The critical thickness for this shift is merely sensitive to the indium composition of the surface monolayer prior to growth. This property…
We relate anharmonic equilibrium thermal fluctuations of smectics A to fluctuations of the Kardar-Parisi-Zhang (KPZ) dynamical model for a growing interface. The KPZ model in 1+1 dimensions is one to one related to a 2D smectic elastic model whose scaling behavior is then obtained exactly. The KPZ model in 2+1 dimensi…
Temperature dependences of the dark conductivity and the photoconductivity for amorphous thin films of Ga 30 Se 70-x In x in the temperature range 298-328 K have been reported. The dark conductivity and the photoconductivity increase at all temperatures as the concentration of In (x=0, 5, 10, 15 and 20) increases. The…
Weak, low frequency disorder induced Raman scattering is observed in nanocrystalline, ‘‘glassy’’ carbon having an in-plane correlation length La≂30 Å. Similar, relatively more intense low frequency scattering is observed after the annealing of amorphous carbon films to 600 °C, suggesting the formation of quite small n…
Thin films of BaTiO3 were deposited on platinum coated silicon substrates by excimer laser (248 nm) ablation at 600 °C or ex situ crystallized at about the same annealing temperature. Films deposited at 600 °C showed good crystallinity and were characterized for ferroelectricity, dielectric constant, dielectric loss,…
Visible photoluminescence has been observed in crystallized a-Si:H/a-SiNx:H multiquantum-well structures at room temperature. The MQW heterostructures consisting of 72 layers were formed by computer controlled plasma-enhanced chemical-vapor deposition method and then crystallized by Ar+ laser annealing technique. The…
Siloxene (${\mathrm{Si}}_{6}$${\mathrm{O}}_{3}$${\mathrm{H}}_{6}$) and its derivatives show strong visible luminescence. By applying semiempirical quantum chemical calculations to the siloxene structure, we demonstrate that the presence of oxygen in a planar array of silicon atoms results in molecular orbitals confine…
We present carbon K emission spectra of diamond excited with high-resolution undulator radiation. The valence-band emission spectra are shown to be strongly dependent on the excitation energy, up to 20--30 eV above the C K edge. It is proposed that the dependence is indicative of the resonant inelastic scattering desc…
Abstract This paper presents a proprietary process developed to manufacture polyurethane (PU) pultruded composites. The blocked isocyanate (NCO)‐terminated PU prepolymer synthesized in this study was prepared from ε‐caprolactam blocked blends of toluene diisocyanate (TDI) and branched polyester. The processability and…