A phase with a glassy appearance has been detected in samples of the Tl–Ca–Ba–Cu system. The presence of such a phase is expected to have a negative effect on the critical current density in a bulk superconductor. Samples of 2-2–2-3 starting composition were prepared from Tl2O3, BaO2, and relatively large particles of CaO and CuO. These samples were then heat-treated at 867°C for various periods of time. The use of large particles of CaO and CuO facilitates the examination of the morphological changes associated with the formation of the superconducting phases. Using scanning electron microscopy, a layer of the 2122 phase was found to form on the surface of the large CaO particles whereas near the surface of the large CuO particles, large voids were observed. By varying some of the experimental conditions, a liquid phase with a composition close to 2-0–2-3 was inferred to form. The voids observed in the surroundings of the CuO particles may be due to the formation of such a melt. This liquid phase, after cooling, apparently leads to the “glassy” phase detected in the reacted samples. This glassy phase may play a role as an intermediate in the formation of the 2122 phase, which could result by a direct reaction between the liquid phase and CaO, A part may remain, however, among the superconducting grains, thus having a negative effect on the critical current density.

Yttria stabilized zirconia powder was synthesized by aerosol pyrolysis of an Y-Zr-nitrate solution. The particles were spherical and had a narrow size distribution, peaking at 0.4 μm. Material made by this process is phase-pure (cubic) and has high chemical purity.

In this paper we report the growth of β–SiC films on Si(100) substrates by low-temperature chemical vapor deposition. Single crystals of β–SiC are grown at temperatures as low as 1150 °C. Low-temperature growth β–SiC is achieved using a SiH4–C3H8–H2–Ar gas system. The growth rate of films grown at 1150 °C is 1 μm/h. Transmission electron microscopy and x-ray diffraction results indicate that the β-SiC films grown at and above 1150 °C are single crystals. Films grown at temperatures lower than 1150 °C are polycrystalline.

Using a computer-controlled inverted torsion pendulum at frequencies near 1 Hz, we determined the mechanical losses in a uniaxially fiber-reinforced composite. The composite comprised glass fibers in an epoxy-resin matrix. We studied three fiber contents: 0,41, and 49 vol.%. Three mechanical-loss peaks appeared: above 300 K, near 200 K, and near 130 K. They correspond closely to α, β, and γ peaks found previously in many polymers. We failed to see a mechanical-loss peak for either the glass or the glass-resin interface. Between 300 and 4 K, the torsion modulus increased in the resin by a factor of 3.30 and in the 0.49 glass-epoxy by a factor of 2.37.

Thin-films of barium titanate (BaTiO3) have been deposited onto single-crystal MgO substrates using pulsed-laser ablation. The early stages of film growth have been examined using transmission electron microscopy by deposition of very thin films onto specially prepared electron transparent thin-foil substrates. The films, which were crystalline as deposited and close to stoichiometric composition, were formed by the nucleation and growth of small islands.

We report on the magnetic-field dependent surface resistance of polycrystalline YBa2Cu3O7 (Tc ≃ 92 K), measured using a brass cylindrical cavity resonator, operating at 16.5 GHz in the TE011 mode. A de magnetic field Happ is applied parallel to the superconducting sample surface, and the temperature dependence of the surface resistance is measured for four different values of Happ (0 T, 0.22 T, 1 T, 5 T). An effective medium theory and the two-fluid model are used to fit the surface resistance versus temperature measurements both in zero field and for various applied fields. These results are applied to characterize the microwave properties of a polycrystalline ceramic superconductor.

The structure and microstructure of a solid state processed Pb-Sr-Ca-Er-Cu-O superconductor have been investigated by transmission electron microscopy. In addition to the majority superconducting phase, at least two other impurity phases have been observed. The superconducting phase is a layered structure similar to the Bi2Sr2CaCu2Oy compound, with an extra Cu atom between the two PbO layers. Stacking defects inside the grain have been observed. A grain boundary amorphous phase has also been observed. The steps in the resistivity-temperature plot and the consequent absence of Tc,0 above 8 K are attributed to either the presence of the Pb2Sr2Cu2Oy unit cell at the grain boundary and/or a local enrichment of oxygen at the grain boundaries. Superlattice spots in the [100] zone axis diffraction patterns from regions enriched in Ca and Er with respect to the nominal composition are interpreted as due to ordering of Sr and Ca/Er in the Sr sites.

Preparation of the superconducting oxide, YBa2Cu3O7−x, was carried out according to the metal alkoxide method. To obtain a homogeneous solution of yttrium, barium, and copper alkoxide in an organic solvent, alkoxides of copper and yttrium were modified by the O-R interchange reaction with 2-dimethylaminoethanol and the structures of their modified alkoxides were studied by 1H-NMR, FT-IR, and EXAFS. The YBa2Cu3O7−x precursor, prepared by hydrolysis of the present solution of alkoxides, was calcined at 850°C for 3 h to give YBa2Cu3O7−x powder as a single phase. This powder was sintered between 900°C and 950°C and characterized for bulk density, microstructure, Tc, and Jc.

Ferroelectric thin film of strontium-barium niobate was successfully fabricated by the sol-gel technique. The films were made on several types of substrate, including quartz, single crystal silicon wafer, and glass slides. The processing temperature was as low as 700 °C. The film obtained with thickness of 3000 Å was dense, transparent, and showed excellent ferroelectricity.

Highly oriented 2212 BSCCO thick films were prepared on polycrystalline MgO substrates using a melt/crystallization technique. Results compare very favorably with those on single crystal materials.1,2 The melting, quenching, and annealing processes were all found to be important in the development of a good microstructure and good superconducting properties. The best results (Jc ∼ 2000 A/cm2 at 64 K and 6000 A/cm2 at 4.2 K) were obtained on films which had been melted, quenched to room temperature, heated to 860°C where they were annealed before slow cooling to room temperature in oxygen, lightly polished, and reannealed at 860°C.

Preliminary results of producing Cu–Y–Ba metallic precursors to high Tc superconductors by high energy ball milling are reported. Mechanical alloying of Cu, Y, and Ba powders (various stoichiometries) produced either amorphous, mixed crystalline/amorphous, or fine grained crystalline powders, as shown by their x-ray spectra. None of the powders exhibited flux exclusion down to a temperature of 1.4 K. The YBa2Cu3 precursor consisted of a mixture of crystalline phases. After being pressed into a pellet and sintered, it was found to be superconducting at liquid nitrogen temperatures.

The adsorption and bonding of CH3, CH2, CH, C2H, and C2H2 fragments to clean and hydrogenated diamond(111) surfaces are investigated in the framework of the atom superposition and electron delocalization molecular orbital method. Low coverage calculations are performed using large cluster models for the surfaces, and high coverages are examined with band calculations on thick two-dimensional slabs with every surface carbon covered by a hydrocarbon fragment (i.e., 1:1 surface coverage). For low coverage adsorption on clean and H-covered surfaces the adsorption energies are in the order C2H>CH ≃ CH2>CH3. In each case, the predominant component of bonding is covalent in character and is a result of overlaps between the sp-hybridized singly occupied dangling surface state orbital on the surface carbon and the sp-hybridized orbital on the fragment carbon atom. While the charge transfer contribution to bonding is nearly the same for CH3, CH2, and CH fragments, it is significantly larger for C2H due to a comparatively stable radical orbital on C2H. C2H2 binds to the surface on the di-σ site where both its ends form bonds to the surface atoms. Onefold adsorption to a H-covered surface is predicted to be unstable. The 1:1 CH3 coverage on diamond(111) is highly unstable because of steric repulsions between adsorbate fragments due to their spacial proximity. This finding is supported by a calculation of the cis-trans isomerization energy of di-t-butyl ethylene, including full structure relaxations. At low coverage CH3 can bind on adjacent surface sites by tilting away from one another. The 1:1 coverage for CH2, CH, and C2H fragments is predicted to be stable on this surface.

Magnetically aligned YBa2Cu3O7-δ ceramics show resistivities approaching that of single crystals and improved transport critical currents in a magnetic field. Reduced microcracking and increased transport along the ab-plane are believed responsible for the improved performance over nonaligned ceramics. Aligned and nonaligned samples were prepared in parallel using a range of sintering and annealing temperatures. A rapid rise in density for samples sintered above 900°C in oxygen is accompanied by rapid grain growth, improved alignment, a drop in the room temperature resistivity, and an increase in the critical current. The presence of low melting point (i.e., Ba–Cu–O-rich) phases at grain boundaries is believed responsible for the rapid densification. However, the presence of this phase does not appear to be the most important factor limiting Jc. A high temperature oxygen anneal at 900°C improved performance as compared to anneals at 500°C, possibly due to the removal of carbon. For aligned samples sintered at 980°C, critical currents are over 200 A/cm2 at 77 K, ¼ tesla, and room temperature resistivities are below 350 μΩ-cm.

Electron-diffraction techniques have been used to study the ordering of oxygen atoms within the Cu(1)O1-δ plane of YBa2Cu3O7-δ. The results show that ordering along a single axis and ordering along two orthogonal axes both occur and alternate systematically across the composition range 0.06 < δ < 0.75. Where the ordering is restricted to a single axis, it is found to be the crystallographic a axis. Various models of oxygen ordering are proposed to explain the observed diffraction phenomena. In addition to the ordering of oxygen atoms that give the diffuse diffraction spots at (h∗/2,0,0) and (0, k∗/2,0), a second type of ordering reflection that occurs at (h∗/3,0,0) and (0,k∗/3,0) was also observed. These sharper and more strongly streaked diffraction maxima are explained in terms of a defect in the cation sublattice.

A transmission electron microscopy study of a post-annealed YBa2Cu3O7−x thin film shows that extra Cu–O planes within the structure can aggregate as stacking faults to form a defect microstructure rather than forming the well-ordered Y2Ba4Cu8O16 phase. Interaction of the stacking faults with the surrounding matrix results in strain effects and microstructural variations which may hinder ordering as well as influencing superconducting properties if occurring in higher concentration. When viewed normal to the plane of the film, the boundaries of the stacking faults can be imaged as dislocation-like defects, indicating the size and shape of the stacking faults and their relationship to other defects such as twins and second phase precipitates.

Polysynthetically twinned crystals of TiAl with a nearly stoichiometric composition have been grown and rolled at room temperature. The maximum total reduction in thickness which is attainable without fracture depends on lamellae orientation with respect to the rolling plane and rolling direction. When specimens are oriented such that shear deformation parallel to the lamellar planes is operative during rolling and its operation causes lengthening of specimens, such specimens can be rolled up to about 50% reduction in thickness. The (111) pole figures are determined for the surface of specimens rolled to several different amounts of reduction, and the formation of surface texture is briefly discussed.

Films containing the metals copper, yttrium, calcium, strontium, barium, and bismuth were grown by organometallic chemical vapor deposition (OMCVD). Depositions were carried out at atmospheric pressure in an oxygen-rich environment using metal beta-diketonates and triphenylbismuth. The films were characterized by Auger electron spectroscopy, Nomarski and scanning electron microscopy, and x-ray diffraction. The results show that films containing yttrium consisted of Y2O3 with a small amount of carbidic carbon, those with copper and bismuth were mixtures of oxides with no detectable carbon, and those with calcium, strontium, and barium contained carbonates. Use of a partially fluorinated barium beta-diketonate gave films of BaF2 with small amounts of BaCO3.

YBa2Cu3Ox was deformed from 850 to 980 °C in oxygen partial pressures of 103 to 105 Pa. Steady-state creep rate, ̇, for P(O2) from 104 to 105 Pa could be expressed as ̇ = Aσ1.0 (GS)−2.8±0.6 exp −(970 ± 130 kJ/mole)/RT, where A is a constant, σ the steady-state stress, GS the average grain size, and R and T have their usual meanings, For P(O2) from 103 to 3 ⊠ 103 Pa, the activation energy decreased to about 650 kJ/mole and for a given temperature creep kinetics were much faster. The data and microscopic observations indicated that creep occurred by diffusional flow. Comparisons with diffusion data for YBa2Cu3Ox suggested that Y or Ba may be rate-controlling diffusing species.

The kinetics of the solid-state reaction Y2BaCuO5 + 3BaCuO2 + 2CuO ⇉ 2YBa2Cu3O6.5−x + xO2 was studied by using x-ray diffractometric and thermogravimetric analyses. Both analyses established that the reaction was well described by the kinetic equation: 1 − 3(1 − F)2/3 + 2(1 − F) = k0 exp(− E/RT)t, where F is the fractional conversion of a calcined powder, E is 520 kcal/molc and, for a rcactant mixture with an average particle size of 3 μm, k0 is 2.03 ⊠ 1092 min−1. An unreacted-core shrinking model was proposed to obtain the particle-size dependence of the reaction, and predicted that the pre-exponential constant k0 changed with reactant particle size by k0 = 2.03 ⊠ 1092(3/d)2 exp(4/d − 4/3), where d is the average reactant particle size in μm.

A combined numerical and experimental investigation into the behavior of diamond (111) surfaces in plasma CVD reactors is presented. Numerically, semiempirical molecular orbital methods are used as a model of diamond (111) surfaces represented by a 20-atom carbon cluster plus surface species. The abstraction of hydrogen atoms by gas-phase hydrogen atoms, the coverage dependence of the heat of formation for submonolayers of CH3 and C2H groups coadsorbed with H, and the energy change for abstraction of H atoms from the surface by various radicals in the gas phase are examined. No barrier to abstraction is found, steric effects in achieving clusters of CH3 groups are large, and C2H and atomic oxygen are found to be the most energetically favored for removal of adsorbed H. Experimentally, relative concentrations of atomic H in the near-surface region as a function of added O2 mole fraction were measured. A weak dependence on O2 concentration is observed, but does not appear to be significant enough to account for observed changes in growth rate. This suggests that other radical species be investigated for their contribution to diamond film growth.