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Critical current density Jc as a function of temperature T and magnetic field H was studied for high quality YBa2Cu3O7-δ (YBCO) films with thickness d=0.2, 1, and 3 μm by means of magnetization measurements of a circular disk in perpendicular field. We found that the thickness dependence of Jc(H) for the YBCO thick films crossovers at high fields for T>50 K, where the 0.2-μm-thick film carries significantly lower Jc(H) than the 3-μm-thick film at high fields, even though the zero- or low-field Jc for the 0.2-μm-thick film is more than twice the value for the 3-μm-thick film. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The mechanisms have been identified for the hetero-epitaxial nucleation of YBa[sub 2]Cu[sub 3]O[sub ∼6.1] (YBCO) at the buried interface between a precursor film and SrTiO[sub 3] for the so-called BaF[sub 2] process which is a postdeposition reaction process for the synthesis of epitaxial YBCO films. It is shown that the preferential nucleation of YBCO at the interface is due to (1) the strong chemical affinity of the (Y, Ba)-oxy-fluoride, an intermediate phase, to SrTiO[sub 3] and (2) the epitaxial alignment of its (111) planes with the (001) surface of the SrTiO[sub 3] which reduces the activation barrier for the formation of YBCO. In thin films (<2–3 μm) the YBCO nuclei, whose c axes are perpendicular to the SrTiO[sub 3] surface, form directly from this aligned oxy-fluoride. In thick films (5 μm), however, this oxy-fluoride decomposes into a disordered transitory cubic phase which then orders to form YBCO nuclei with three orientational variants, one with its c axis perpendicular and two with their c axes parallel to the (001) plane of SrTiO[sub 3]. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Studies the superconducting transport properties of 2.2-GeV gold-ion irradiated c-axis twist Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8+delta] bicrystals. Determination of the increase in irreversible temperatures within the single crystals and across the grain boundaries after irradiation; Effect of heavy ion irradiation on critical current.

Superconducting critical current densities Jc of pure and alloyed Nb3Sn layers of bronze processed monofilamentary wires were measured at 1.8 and 4.2 K in magnetic fields up to 24 T. The maximum in Jc at 20 T was found for Nb3Sn layers which were fabricated using (Nb ∼3.3 at. % Ti) cores, and the values of Jc were ∼670 and ∼370 A/mm2 at 1.8 and 4.2 K, respectively. These values are ∼5 and ∼25 times greater than those for ''pure'' Nb3Sn wires at these same temperatures. The functional dependence of Jc on the Ti content was also identical to that for the measured values of Hc2 vs Ti content for these wires. The maximum value of Hc2 of the wires with the matrix in place was 26.3 T for the wire which was fabricated from the core containing 3.3 at. % Ti in Nb. [ABSTRACT FROM AUTHOR]

Using an electron diffraction technique, the thicknesses of the (nonorthorhombic) twin boundary layers were measured for pure and alloyed YBa2(Cu1-xMx)3O7-δ. Boundary thickness varied from ∼0.7 nm for M=Ni, x=0.02, and δ[bar_over_tilde:_approx._equal_to]0 to ∼2.6 nm for M=Al, x=0.02, and δ[bar_over_tilde:_approx._equal_to]0, while it was ∼1.0 nm for a pure YBa2Cu3O7. High-resolution transmission electron imaging of similar specimens supports the existence of such twin boundary layers. [ABSTRACT FROM AUTHOR]

Investigates the irreversible field of superconducting bismuth-2223/silver tapes with columnar defects. Irradiation of the tapes with lead ions; Limitation for the field application of the tapes at liquid nitrogen temperature; Efficiency of columnar defects as pinning centers.

Investigates the angular distributions of large-angle grain boundaries of Bi(2:2:1:2) and Bi(2:2:2:3) composite tapes by electron microscopy. Use of the Coincidence Site Lattice Theory; Illustration of the surface morphology of the tapes; Importance of the high degree of alignment among crystals.

Examines the sample size effect on the determination of the irreversibility line of high T[sub c] superconductors. Similarity of flux line pinning strength between tape and grain-aligned specimen; Use of direct current magnetization method in line determination; Factors controlling superconductor magnetic irreversibility.

Powder metallurgy processed Nb3Sn(Ti) superconducting wires were fabricated with Sn x wt. % Ti cores for 0≤x≤3, 16 or 22 vol % cores, and a Cu 45 wt. % Nb composite. The processing used swaging, cold hydrostatic extrusions, wire drawing and heat treatments of 750 °C for two to four days. Nominal areal reductions of 104 were used. Hydride-dehydride Nb and rotating electrode processed Nb powders gave the same performance. Overall critical current densities Jc were measured between 4.2 and 1.8 K for applied fields up to 23 T. Jc increased with increased Ti and/or Sn content. The Nb3Sn(Ti) wires using a Sn 3 wt. % Ti, 22 vol % core gave Jc >104 A/cm2 at 20 T and 4.2 K and Jc =104 A/cm2 at 23 T at 1.8 K. Removal of the precompression of the matrix increased Jc by about a factor of 2 at 20 T and 4.2 K. [ABSTRACT FROM AUTHOR]