Peter J. Bednarczyk

The preparation of “1223” Tl-Ca-Ba-Cu-oxide superconducting films via the reaction of silver-containing spray deposited Ca-Ba-Cu-Oxide with thallium oxide vapor

Abstract A process is described for the preparation of superconducting films of “1223” TlxCa2Ba2Cu3Oy (0.65 10 000 A/cm2 was measured at 60 K-2 T with the magnetic field applied parallel to the crystallographic c-axis of the film.

Transport critical currents in spray pyrolyzed films of TlBa2Ca2Cu3Oz on polycrystalline zirconia substrates

Large critical currents with a relatively weak magnetic field dependence are obtained in thick films of TlBa2Ca2Cu3Oz. Transport measurements indicate Jc ≳105 A/cm2 at 77 K, zero field, and Jc≳104 at 60 K in a 2 T field applied along the c‐axis. The observed behavior is attributed to a large degree of uniaxial alignment of platelike grains, and to superior intragranular flux pinning. These results are consistent with recent theories concerning the nature of vortices in highly anisotropic (layered) superconductors and ‘‘brick wall’’models of intergranular current transport.

Enhanced transport critical current at high fields after heavy ion irradiation of textured TlBa2Ca2Cu3Oz thick films

Spray pyrolyzed T1(1223) films deposited on polycrystalline YSZ substrates are characterized before and after heavy ion irradiation. A factor of 2 decrease in zero field critical current is observed. However, significantly improved critical current is found at fields above 1 T, where intragranular effects dominate. The irreversibility line at 5 T is shifted by ∼20 K to higher temperatures. Scaling of the data before and after irradiation and at different temperatures is modeled by an expression which interpolates between single vortex pinning and collective creep.

Superconducting joints formed between powder-in-tube Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub z//Ag tapes

Superconducting joints between Ag-clad, Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub z/ tapes have been obtained with approximately 1/2 the current capacity of the tapes themselves. The Ag sheath is removed from one side of each tape without significantly disturbing the superconducting core. The exposed superconducting core of the two tapes is brought into contact and pressed so as to again seal the superconductor in a Ag sheath. A reaction anneal is performed to join the two cores together and repair damage associated with the removal of Ag and the pressing. Transport measurements using multiple voltage taps have been found useful in characterizing the critical current variation across the joint.<<ETX>>

An alternate preparation for (Bi, Pb)2Ca2Sr2Cu3Oz

Abstract An alternative synthetic route for obtaining (Bi, Pb) 2 Ca 2 Sr 2 Cu 3 O z (2223), by using Bi 2 CaSr 2 Cu 2 O z , (2122), as a starting material is described. The advantages of this route include lower processing temperatures, shorter reaction times, and improved phase purity over conventional synthetic routes.

Critical current as a function of film thickness for spray pyrolyzed films of TlBa2Ca2Cu3Oy

Abstract It is imperative for tape applications to produce thicker films of TlBa 2 Ca 2 Cu 3 O y with high critical current density on polycrystalline substrates (a useful figure of merit is the critical current per unit width, with a reasonable goal being 10 A mm −1 ). We have studied the critical current density at 77 K, 0 T ( J c ) as a function of film thickness in the range 2 to 10 μm. A key parameter for obtaining a high J c was found to be the film density; films with relative density > 82% showed much higher values of J c . Based on average values, J c was found to peak at 60 kA cm −2 for samples 2.5 to 5 μm thick (corresponding to 3 A mm −1 for 5 μm thick samples), and to decrease for thicker samples, yielding 3 to 3.5 A mm −1 from 5 to 10 μm. There are individual segments with values as high as 8.4 A mm −1 .

Critical current, film thickness and grain alignment for spray-pyrolyzed films of TlBa2Ca2Cu3Ox

Abstract X-ray diffraction rocking curves are used to measure the c axis alignment of TlBa 2 Ca 2 Cu 3 O x films grown on polycrystalline substrates with thickness varying from 3 to 10.5 μm. Films thicker than 3 μm are found to contain two layers: a well aligned (3.5° FWHM) bottom layer, and a poorly aligned (greater than 12° FWHM) top layer. Azimuthal scans show that the component with good long-range out-of-plane alignment retains its characteristic colony microstructure of local in-plane alignment as film thickness increases. The length dependence of the critical current density may be accounted for by assuming that all the supercurrent is carried by the well-aligned component.

Critical current density and microstructure of 7–8 μm thick spray pyrolyzed films of TlBa2Ca2Cu3Oy

Abstract Tape applications require high values of critical current density in thick films of TlBa 2 Ca 2 Cu 3 O y (Tl-1223). Previous work on polycrystalline YSZ substrates has shown average values of J c (77 K, 0 T) = 60 kA cm −2 for films 3–5 μm thick. The effect of varying the substrate temperature (853–868°C) during thallination in a two-zone flow-through furnace is studied here for thicker films (7–8 μm thick). Film density and the zero-resistance transition temperature increase with increasing processing temperature, as does the amount and size of the plate-like features on the film surface. X-ray diffraction shows that alignment improves with increasing temperature, but is still below values obtained for 3 μm thick films. Phases other than Tl-1223 were found at all processing temperatures. Values of J c for the 7–8 μm thick films are generally lower than for the thinner 3–5 μm thick ones, but the current per sample width can be higher (the highest value for the thinner films was 5 A mm −1 , whereas at substrate temperatures > 860°C, 7% of the segments of the 7–8gmm thick films had values A mm −1 .

Texture and transport in spray pyrolyzed TlBa 2 Ca 2 Cu 3 O 9 thick films

©1995 Materials Research Society. The original publication is available at: http://www.mrs.org/

Low-signature Cadmium Zinc Telluride CZT defect inspection by IR, ultrasound, etch pit density, and x-ray topography

Widespread utilization of Cadmium Zinc Telluride (CZT) in nuclear radiation detectors is currently limited by the cost of high spectroscopic quality material. Yield of devices is limited by non-uniformity in the charge collection efficiency associated crystal defects that occur during synthesis. An inspection method suitable for grading CZT parts during an early stage of device manufacturing is sought. We have implemented a combination of UT and IR imaging of CZT wafers that is successful to map sub-grain boundaries, twins and tellurium inclusions greater than 10-micron diameter. However, point defects and dislocations are below the imaging resolution of the system. It is the goal of this system to study defect density in UT and IR clear areas of CZT wafers and establish an opportunity for low signature defect mapping.