Differential thermal analysis (DTA) and thermal gravitometry analysis (TG A) under flowing oxygen show that the formation temperatures of the high Tc T12Ca2Ba2Cu3Ox (2223) and the low Tc T12CaBa2Cu2Ox (2212) phases lie at around 910 °C and 840 °C, respectively. The activation energies are as low as 50 kcal/mole for the 2223 phase and 35 kcal/mole for the 2122 phase. Thus the time for the formation of these phases can be within 30 minutes.

Two preparation methods were tried, and the one with Ca3BaCu3O7 as a precursor was easier to attain pure high Tc 2223 phase than that prepared directly from component oxides and carbonates.

Single-phase samples of T12Ba2CaCu2O8 and T12Ba2Ca2Cu3O10 have been prepared using a reliable and simple synthetic method. Samples were characterized by x-ray powder diffraction, magnetic susceptibility and four probe resistivity methods. The Tc R=0 values for T12Ba2CaCu2O8 ranged from 100 to 105K, whereas those for T12Ba2Ca2Cu3O10 ranged from 96 to 107K. The relationship between the superconducting properties and the various preparation conditions are discussed.

A technique for the identification of individual anisotropic grains in a heterogeneous and opaque material involves the observation of grain color in a reflecting light optical microscope. Such colors are generally characteristic of particular phases. We have studied the presence of color in many superconducting cuprates and found a strong correlation between color and the existence of superconductivity. The change in color from insulator to superconductor facilitates the selection of grains for microanalysis. Color variations in a Tl-Sr-Ca-Cu-O material are investigated using quantitative energy dispersive x-ray spect-roscopy. Cation concentrations are found not to correlate with the changes in color. This apparent lack of correlation of color with composition is discussed.

Tl-based superconductors of initial composition Tl:Ca:Ba:Cu equal to 2:2:2:3 and 1:3:1:3 were heated in oxygen at pressures of 104 to 6 x 105 Pa. The 2:2:2:3 composition formed primarily the 2-layer superconductor with zero resistance from 77 to 104 K. The 1:3:1:3 composition formed nearly phase pure 3-layer superconductor with a maximum zero resistance temperature of 120 K. Application of hyperbaric pressure influenced phase purities and transition temperatures slightly; phase purities decreased significantly with application of hypobaric pressures.

The fabrication of bulk YBa2Cu307-x/metal composite superconductors is not easy because of the oxygen-temperature dependence of the YBa2Cu307-x phase (the socalled 123 phase). A loss of oxygen occurs during consolidation of these composites at high temperature and it is almost impossible to diffuse oxygen through the metallic envelope into the densified compound to restore the required oxygen content for superconductivity above 77K. To overcome this drawback, a one-step synthesis and consolidation process was used to produce YBa2Cu4O8/ nickel composites. The superconductive 124 phase has a more stable oxygen stoichiometry [1] and is synthesized under a high oxygen pressure at high temperature.

Powders of YBa2Cu4O8 (“124”) were prepared via solid state reaction of Y2O3, BaCO3, and CuO. The mixed precursors were heated in flowing oxygen of reduced total pressure, followed by cooling and annealing at 750°C under ambient pressure oxygen.The procedure produced orthorhombic 124 as the main phase, with YBa2Cu3Ox (“123”) as a minor impurity phase. Phase purity improved, and nearly phase-pure 124 was obtained, upon annealing the as-calcined powder in flowing oxygen at 800°C.

Samples of YBa2Cu3O7-x were prepared by the solid state reaction method using Y2O3, CuO, and either BaCO3 or Ba(NO3)2. The samples were studied using DTA-TGA, Knudsen cell mass spectrometry, and SEM-EDAX. The results indicated that C was more abundant in samples prepared from the carbonate than from the nitrate. In both samples, C was more abundant than N which was at low levels in both samples. Knudsen cell mass spectrometry has proven to be an experimental technique which is sensitive to volatile impurities at low levels.

YBa2Cu3O7-x (123) powders containing silver have been prepared by aerosol decomposition. Metal nitrate solution droplets were decomposed at temperatures above and below the melting point of the Ag-O eutectic. In both cases, the Ag was present as a separate grain attached to YBa2Cu3O7-x. Individual aerosol particles had dimensions of 50 – 1000 nm. Grain sizes of Ag and 123 crystallites within these particles were 10 to 100 nm. Larger 123 grain sizes could be obtained by varying the reactor operating conditions. The powders provide a source of material for generation of YBa2Cu3O7-x/Ag ceramics with smaller Ag and 123 grain sizes and more uniform composition than can be obtained by other methods.

Y1Ba2Cu3O7 has been prepared by the evaporative decomposition of solutions method. Nitrate and mixed anion solutions were atomized and decomposed at temperatures ranging from 300°C to 950°C. The resulting materials have been characterized using x-ray powder diffraction, Thermal Gravimetric Analysis (TGA), particle size analysis, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The powder consists of 0.3 micron agglomerated hollow spheres with a primary particle size of 0.06 micron. TGA and x-ray diffraction indicate the presence of barium nitrate and barium carbonate due to incomplete decomposition and/or product contamination by the process environment.

Four kinds of YBa2Cu2Ox (YBCO) superconducting powders with different particle sizes, shapes and different amounts of twins have been prepared in this work. The density, grain sizes, XRD of phase composition, configuration of twins of the ceramics have been investigated. The relation between the characteristics of YBCO powders and the microstructure, current density of the bulk materials are also discussed. In contrast to the YBCO powder prepared by solid state method, the YBCO powders through the improved coprecipitat ion approach have less impurities, smaller particle size and much more amounts of twins, as well as the sintered pellets show a higher density, an orthorhombic single phase, and moreover, the pellets have finer grain boundaries and well developed twins. As a result these samples exhibit current densities (about 1500 A/cm2) higher than those prepared by solid state method. Using BaOx instead of BaCO3 as the starting material, a more dense bulk YBCO ceramics with orthorhombic single phase and Jc (about 1,000 A/cm2) can have also been fabricated by solid state mat hod.

The copper(II) alkoxide, bis(2-(2-ethoxyethoxy)ethoxide)copper(II), was prepared and had a solubility in organic solvents greatly exceeding those of simple copper(II) alkoxides (>0.4 mol/L in toluene at room temperature). Copper 2-(2-ethoxyethoxy)ethoxide (2-(2-ethoxyethoxy)ethoxide = 2,2-EEE) toluene or toluene/THF solutions gelled upon exposure to moisture. These solutions were hydrolysed with 0.2, 1.0, 2.0, 4.0, and 20.0 equivalents of H2O and the resulting powders were characterized by IR spectroscopy and SEM.

Results are presented on efforts to prepare both the 80K, Bi2CaSr2Cu2Oz (2122), and 11 OK, (Bi,Pb)2Ca2Sr2Cu3Oz (2223), transition temperature bismuth superconducting species in either phase pure or nearly phase pure, powdered form using either equimolar NaCI-KCI or NaBiOz as molten fluxes. Data are presented on the effects of variation of the reaction temperature and duration, solvent content, relative CaO and CuO contents, and of post-synthesis anneals of the product materials.

The oxalate route was used to prepare (Bi-Pb) -Sr-Ca-Cu-O powder with the nominal composition Bi1.75Pb0.4Sr1.3Ca2.1Cu3.2Oy. This powder was decomposed/annealed at different temperatures between 434 and 795°C. They were investigated by thermogravimetric analysis, X-ray diffraction and transmission electron microscopy. Particle size distribution and surface area were also determined. The specific surface area decreased from a value of 16.5 m2/g for powder decomposed at 434 °C to 1.0 m2/g for powder decomposed at 795 °C. The measured mean particle size reached a minimum of 0.52 juri for powder decomposed at 589 °C.

New powder synthesis Methods have been developed for preparing the single-phase T12CaBa2Cu2O8 (the 2122 coapound) and T12CaBa2Cu3O10 (the 2223 coapound) powders froa stoichioaetric reactant mixtures. The 2122 coapound was prepared froa a stoichioaetric Mixture of T12O3, CuO, and CaBa2CuO4, while the 2223 coapound was prepared froa the same aixture but with additional CaO and CuO to Batch the correct (T1:Ca:Ba:Cu=2:2:2:3) stoichioaetry. The single-phase 2122 saaples with Tc above 110 K were obtained by using one-step calcination at 830°C, while the 2223 saaples with Tc ranging between 115 and 120 K were obtained by employing a first calcination at 830°C for 5 hrs and a second calcination at 870°C. Powder aelting, which is strongly associated with the conventional aethods, was significantly suppressed in the new aethods.

The Rocketdyne Division of Rockwell International has developed a large scale spray-calcination technique generic to the preparation of ceramic high-temperature superconductor (HTSC) powders. Among the advantages of the technique is that of producing uniformly mixed metal oxides on a fine scale. Production of both yttrium and thallium-based HTSCs has been demonstrated using this technique.

In the spray calciner, solutions of the desired composition are atomized as a fine mist into a hot gas. Evaporation and calcination are instantaneous, yielding an extremely fine, uniform oxide powder. The calciner is 76 cm in diameter and can produce metal oxide powder at relatively large rates (approximately 100 g/h) without contamination.

Bulk samples of thallium-based powder were prepared by spray calcination, collected, cold-pressed, and sintered. An optimized temperature schedule was developed to produce T12Ba2Ca2Cu3Ox. Samples were examined by X-ray diffraction and characterized by measurements of critical transition temperature, Tc. A complete transition to zero resistance at 112 K was measured.

Continuing an earlier study, we report new data on the orientational effects of magnetic field alignment of some bismuth cuprates and 8 additional thallium cuprates. Strong parallel alignment is seen for Lu bismate and Nd, Sm and Ho thallate; strong normal alignment is seen for Tm; however, in contrast to bismates and 123 phase, Tl cuprates show little anisotropy among directions within the basal plane.

High-purity (99.999%) Y2O3 powder is used as a starting material for fabricating high-temperature superconductors (HTS), and is frequently found as an unreacted second phase in the final product. We have found that as-received Y2O3 contains Tb3+ paramagnetic impurity ions as determined by TSL and emission-spectra measurements. Deep luminescence traps (presumably Tb4+ ions) are formed in Y2O3 when it is exposed to frays, x rays, or fluorescent lights. These deep traps can only be removed by annealing the material to near 1600°C. Given the short coherence length of HTS it is possible that order-of-magnitude variations in the Tb impurity concentration of starting materials may affect the ultimate value of surface resistance (Rs).

The pulsed laser evaporation (PLE) technique for deposition of thin films is characterized by a number of unique properties. Based on the experimental characteristics, a theoretical model is developed which considers the formation and anisotropic three dimensional expansion of the laser generated plasma. This model explains most of the experimental features observed in PLE. We have also employed the PLE technique for in-situ fabrication of YBa2Cu3O7 superconducting thin films on different substrates in the temperature range of 500–650°C. At temperatures below 600–C, a biased interposing ring between the substrate and the target was found to significantly improve the superconducting properties. The minimum ion channeling yields were between 3-3.5 % for films deposited on (100) SrTiO3 and (100) LaA1O3 substrates. The films exhibit very high critical current densities (Jc) with maximum values exceeding 6.5 x 106 amps/cm2 for silver doped YBa2Cu3O7 films on (100) LaA1O3 substrates, and the Jc also varies anisotropically with the magnetic field.

Pulsed KrF (248 nm) laser ablation has been used for in situ growth of smooth, high‐quality YBa2Cu3O7‐x epitaxial films of variable thickness on SrTiO3, KTaO3, LaGaO3, LaA1O3, cubic ZrO2, and MgO substrates, at temperatures of ∼60O‐730°C, without higher temperature post‐annealing. A rotating target pellet, fine focusing by a single cylindrical lens, laser‐beam scanning over the target, and laser energy densities ∼2.5‐3 J/cm2 can be combined to yield films of completely uniform composition and with ∼25% thickness variation over areas ∼8 cm2. The best films have Tc > 92 K and JC(H = 0, T = 77 K) > 2 MA/cm2. Film‐growth procedures are described, together with results of superconducting and normal‐state transport measurements.

We have deposited YBa2Cu307.$ thin films onto <100> SrTi03 substrates at 700°C as a function of target‐substrate bias (0 to 300 V) in order to make use of the positive ions in the laser produced plume to assist in the deposition. The films were extensively characterized to determine differences in film properties (composition, structure, and transport). The results suggest that film properties were optimized at or near a target‐substrate bias of 100 V, although, the differences in film properties were within the margin of reproducibility.