The oxygen-deficient orthorhombic oxide YBa2Cu3O7-δ has been the center of intense recent interest because of its high Tc superconducting proper-ties[l-3]. Recently, the structurally related La3Ba3Cu3O15-δ, has received increasing attention[4–9]. The pure Y analog[10,11] cannot be synthesized by usual solid state reaction routes probably because of its metastability near 880°C. Here we report on the successful synthesis of pure tetragonal Y3,Ba3CU6O15-δ (referred to as Y 3–3–6), via the firing of an atomically mixed citrate precursor at a relatively low temperature. X-ray diffraction data characterize Y 3–3–6 to be isostructural with the corresponding La compound[4]. The unit cell composition can then be written as: Y(Ba2−x Yx) CU3O7+δ with the parent compound at x = 0.50. Specimens of Y 3–3–6 at × = 0.50 and 0.375 annealed at 650°C under 1 atmosphere of O2 are non-superconducting. Higher pressure O2 annealing and fluorine-doping leads to a 1–5% superconducting volume fraction with onset at 85K. Annealing near 880°C creates a 10% superconducting fraction which shows near-zero resistivity at 62K and a reproducible, small resistive transition near 260K.

After the November/December issue of Journal of Materials Research was released to the printer, the authors discovered a typographical error in the numbers on Fig. 7 of their article. The binding energies in Fig. 7, which now read 936–924 eV, should read 536–524 eV. Please see the corrected figure that is included in this erratum.

A series of poly-(arylene vinylenes) has been investigated by means of Resonance Raman Scattering and infrared absorption. The behaviour of the Raman spectra of compounds with benzene rings (PPV) or with heteroaromatic rings (PTV or PFV) as a function of the excitation wavelength is reported. Valence force-field calculations are performed to assign both Raman and IR vibrational modes and in order to reach better sets of force constants, we use model compounds from which parameters can be, in a first step, transferred to the polymer. In the case of polythienylene vinylene (PTV) for example, thiophene, trans-bis-(2-thienyl) ethylene (TTE) as well as polythiophene and thiophene oligomers are used. For a better consistency all over the series, we find from our calculations that an assignment slightly different from the one proposed in the literature has to be considered, in particular concerning the C-C stretching mode inside the thiophene ring. Results applied to polyfurylene vinylene are in good agreement with experimental data.

Symmetry-breaking structural and charge oscillations are calculated for (C(p)H(p))- lattices (p = 5 to 9) and used to predict Coulombic expansion coefficients, x-ray photoelectron spectra, and crystallographic features that can be compared with experimental results. Extension of these predictions to other dopant concentrations is provided by derived analytical expressions. The parameters for the infinite lattices are derived from oligomer-ion results obtained from modified neglect of differential overlap calculations. Such calculations on oligomer ions with different parametrizations provide essentially identical changes in charge and structural parameters upon doping and these changes are in excellent agreement with the results of infinite-chain calculations. The degree to which oligomer-ion segments retain the structural parameters of charged arrays for the infinite lattice is remarkable. Derived geometries and charge distributions indicate two different types of charged defects, solitons (or antisolitons) and split solitons (or split antisolitons), and the geometry and charge distribution of the latter defects is shown to correspond to the average of those for two soliton lattices that have a relative shift of two CH units. At least in the absence of an external Coulomb field, soliton and split-soliton lattices for p odd are quasidegenerate, and the lattices for p even consist of alternating sequences of solitons and split antisolitons. Large oscillations in local chain-axis direction are predicted, which is a consequence of both oscillations in bond angles and the nonequivalence of even (and odd) bond lengths. Including these effects provides predicted Coulombic expansion coefficients that are in good agreement with observations for Na-doped polyacetylene. Much smaller bond-angle oscillations are predicted for anion lattices than for cation lattices, which can be at least partially explained by Coulomb effects. Observed C-13 NMR chemical shifts are consistent with predictions for oligomers, and good agreement is obtained between calculated and observed x-ray photoelectron spectra for sodium-doped polyacetylene. Emphasis is placed on the results of crystallographic studies of alkali-metal-doped polyacetylene and on the relationship between the experimentally derived symmetry breaking in interchain packing and the molecular symmetry breaking predicted by theory. Since presently available experimental data are insufficient for complete determination of structure, the present theoretical results can be useful for refinements in the interpretation of these data, as well as for refined crystal-packing calculations.

We report studies carried out experimentally and theoretically on a series of poly(arylene vinylene)s: PPV, PTV and PFV. Raman and infrared spectra are described and analyzed in the frame of a dynamical model based on valence-force-field calculations. In order to achieve good fits and to obtain reasonable sets of force constants, we have used different series of model compounds, such as trans-stilbene and distyryl-benzene in the case of PPV, and thiophene, trans-bis(2-thienyl)ethylene (TTE) in the case of PTV. It turns out that such compounds are necessary to obtain consistent results. In the case of PTV, for example, we found from calculations that an assignment slightly different from the one proposed in the literature has to be considered concerning the CC stretching mode of the thiophene ring. An extension of these results to PFV leads to a good assignment of both IR and Raman modes in agreement with experimental data.

We have performed a normal mode analysis and used a newly developed vibrational analysis method for polymers, based on ab initio calculations for large oligomers, to determine the valence force field of poly(p-phenylene vinylene) (PPV), poly(thienylene vinylene) (PTV) and related polymers, and to calculate theoretical IR and Raman spectra of these oligomers and polymers. The calculated C-C stretch constants are used to describe the structure of neutral and doped PPV in terms of bond lengths r and DELTA-r, the bond length alternation parameter. The results are compared to bond length alternation patterns from MNDO for cations (polarons) and dications (bipolarons) of large model oligomers. The results favor the formation of bipolarons in PPV.

In this work, a complete assignment of Raman and IR modes is reported for both poly(thienylene vinylene) and poly(furylene vinylene) whose chains are composed of an alternation of aromatic rings and vinyl groups. In order to achieve these attributions, we have developped a valence force field model. The vibrations of an aromatic ring show some similarities in a series of compounds with the same cycle. So the same set of parameters is used to calculate vibrational modes for both polymers and model compounds such as trans-bis(2-thienyl)ethylene, a molecule composed of two thiophene rings separated by a vinyl group. Therefore, we present an experimental comparison between Raman spectra of poly(thienylene vinylene), thiophene and trans-bis(2-thienyl)ethylene, and the assignment of the vibrational modes in the latter molecule is also discussed.

The tetragonal (T c=55 K) and orthorhombic (non-superconducting) Tl2Ba2CuO6 (Tl 2201) phases have been synthesized by aca 20 GPa planar shock wave in a microsecond time frame. Because of local rapid quench rates (up to 106 K/s) defects related to metastable phases are frozen in the sample. In the 2201 phase the predominant defect identified by high resolution lattice imaging corresponds to a Tl-Ba-Cu-Tl-Cu (Tl 1212) phase which is metastable but can be synthesized via a low temperature reaction. Defects of this type may account for the enhanced flux trapping observed in the material using field modulated microwave absorption. Attempts at shock synthesizing the more complex Tl2Ba2CaCu2O8 and Tl2Ba2Ca2Cu3O10 phases are also discussed. Shock processing pre-synthesized YBa2Cu3O7 powder in the radial geometry followed by an O2 anneal at 890 C produces near-theoretical density cylinders that sustain inter-grain critical currents at zero field of 1350 and 750 amps/cm2 at 60 and 77 K respectively. The magnetic field dependence of the critical current and the magnitude of flux-pinning in this material relative to sintered pellets are enhanced by a factor of 2–3. Preliminary investigations of the defect microstructure of this material are discussed.

Resonance Raman scattering data are presented for both polyparaphenylene and polyphenylene-vinylene for different excitation wavelengths. Both undoped and p-doped polymers have been studied. By using a dynamical model based on valence-force-field calculations, all IR and Raman vibrational modes have been assigned and sets of force constants determined. In the case of doped polymers, new Raman modes were observed in both compounds and new calculations have been performed. Different values were obtained for the force constants which agree well with the presence of a quinoid structure along the chains.

A novel electrochemical process has been developed for the formation of superconducting films. Using this process, superconducting films of Bi2Sr2Ca1Cu2O8 and (Pb,Bi)2Sr2Ca1Cu2O8 have been formed. The process consists of simultaneously depositing the metallic constituents of the superconductor from a single electrolyte, and thermally oxidizing the resulting precursor film to form the superconducting phase. Application of −4 to −5 V vs Ag/Ag+ to a conductive cathode substrate, immersed in an electrolyte containing salts of all of the metals, reduces the metal cations causing them to deposit on the cathode as a metallic film precursor. Precursor films having desired stoichiometries were obtained by regulating the electrolyte bath composition.

The synthesis procedure and superconducting properties of the first two members of the new series of superconductors of a general formula: (Tl, Pb)1 Sr2 Can−1 Cun O2n+3−δ , are reported. The detailed atomic level microstructure of the compounds have been determined and computer simulated with structural models. Tc increases with n, the number of Cu-O2 layers per unit cell, as in the single Tl-layer Tl-Ba-Ca-Cu-O compounds, but the new materials have higher Tc ’s for the same value of n.

The aim of the present work is to investigate the conformational change of conjugated chains upon doping by small angle neutron scattering. Polymer solutions such as n-butylthiophene (C 4 HS(CH 2 ) 3 CH 3 ) n doped with NOSbF 6 can provide such a goal. For the neutral chains, results show that, at room temperature, even for the lowest polymer concentration studied (c p = 0.1 mg/cc), a positive interchain interaction occurs. At higher temperature (T = 65°C), an isolated chain behavior can be measured allowing to measure the statistical length b = 55 A ̊ and the extension of the lateral groups L t = 12 A ̊ . With a polymer concentrationsas low as c p = 0.5 mg/cc and a dopant concentration equivalent to one dopant molecule per monomer unit, the chain conformation is modeled by a rod structure, b > 850 A ̊ . At the same dopant concentration, but with c p = 2.4 mg/cc, the scattering function show a q −2 behavior. In any case, no correlation hole is observed, which differs markedly from the usual behavior observed in polyelectrolyte solutions.

The three copper layer ∼ 110 K Bi2Sr2Ca2Cu3O10+δ phase has been prepared as a nearly pure compound by alloying with Pb under various oxygen pressures, and by long-term annealing. Studies of the superconducting properties and the atomic level microstructure of these samples using high resolution electron microscope imaging, are reported. The role of the substituent atoms in producing the 110 K phase is briefly discussed.

We report the shock-wave synthesis at a yield ≳80% by volume of the single copper layer thallium superconductor of composition Tl2Ba2CuO6. The as-synthesized material displays zero resistance near 55 K and a diamagnetic onset to bulk superconductivity at 70 K. Lattice imaging indicates that the superconducting microcrystals consist of a novel defect microstructure involving an intergrowth of two copper-oxygen layers probably interleaved by partial thallium and barium occupancy.