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The addition of artificially induced defects improves the pinning efficiency of magnetic flux vortices in YBa2Cu3O7-δ (YBCO) films. In YBCO films by pulsed laser ablation (PLD) technique this goal can be pursued by the introduction of epitaxial second phase nanoinclusions in the YBCO matrix. In the present work, the effect of BaZrO3 (BZO) inclusions in stoichiometric YBCO films on transport properties has been studied. Composite targets obtained by addition of BZO powder in molar percents ranging from 2.5 to 7 mol. % have been prepared with BZO mean grain size of about 1 μm. Structural and morphological characterizations of the films obtained by PLD from these targets have been carried out through X-ray diffractometry and Scanning Electron Microscopy (SEM) analysis. Dc electrical transport measurements at 77 K have revealed a better magnetic field retention of the critical current density, Jc, being at 3 T the 14.6% and the 16.4% of the zero field values for YBCO-BZO 5% and 7%, respectively. The complex surface impedance has been measured by means of a dielectric resonator at a high microwave frequency (50 GHz). In order to identify the potentially strong pinning induced by the inclusions, the field-dependent complex resistivity has been determined as a function of temperature in a moderate magnetic field (B < 1 T). Very high depinning frequency are estimated in YBCO films with BZO inclusions indicating extremely high vortex pinning and steep potential wells. [ABSTRACT FROM AUTHOR]

A CeO2/YSZ/CeO2 buffer layer structure was epitaxially deposited by pulsed laser deposition on a Pd seed layer grown on non magnetic Ni88 Cr8W4 alloy. Structural analyzes performed by x-ray diffraction and EBSD show a good texture, with typical YBCO FWHM of about 5° and 8.5° for in-plane and out-of-plane orientations, respectively. About 300 nm YBCO films deposited by PLD on such a buffer layer structure, show typical values of critical temperature of about 89 K and a critical current density greater than 0.6 MA/cm² at 77 K and self field. [ABSTRACT FROM AUTHOR]

Abstract: The improvement of the critical current density in YBCO coated conductor tapes necessarily concerns the study of grain boundary (GB) properties and the study of different pinning mechanisms involving both GB and the interior of the grain (IG). Recently, it has been proposed that the introduction of Ca substituting Y enhances J c in YBCO grain boundaries (GB). On the other hand enhanced correlated pinning, as observed in YBCO thin films grown on CeO2 buffered substrates, has been ascribed to elongated defects along the c-axis of the film. In order to evaluate the role of calcium and CeO2 buffer layer on the superconducting transport properties of YBCO films, critical current density measurements as a function of temperature, magnetic field and angle between magnetic field direction and c-axis of the film have been performed on epitaxial thin films of unsubstituted and 10at.% Ca substituted YBCO grown on CeO2 buffered Al2O3 single crystal substrates. Results are compared with data obtained on 10at.% Ca substituted YBCO grown on SrTiO3 single crystal substrate. [Copyright &y& Elsevier]

We investigate the effect of partial substitution of Y by Ca in YBCO superconducting thin films. The films were grown on (1 0 0) SrTiO3 single crystal substrates by pulsed laser deposition (PLD). The Ca doped film were ablated from Y1−xCaxBa2Cu3O7−δ targets with x=0, 0.05, 0.07, and 0.10. The dc transport properties of the films in applied magnetic field are analyzed to study the role of Ca on the superconducting properties of YBCO films. The irreversibility line for the samples with x=0 and 5 at.% Ca was derived from the E–J curves using a scaling theory for the vortex-glass transition. [Copyright &y& Elsevier]

The epitaxial oxidation of the (0 0 1)[1 0 0] textured Ni100−xVx tapes was studied because of the practical interest of NiO as a first buffer layer for the YBCO based coated conductors. The study revealed that the oxidation of the Ni–V alloy is rather complex, the less noble V being internally oxidized, while Ni undergoes an external oxidation. Moreover, the formation of the NiVO3 and of Ni7V5O17 compounds have negative effects on the epitaxial oxidation and on the surface morphology, as well. The role of vanadium on the epitaxial oxidation of Ni–V alloy has not been fully understood yet. The optimum conditions for the epitaxial oxidation have been found to be: 700C, t<30 min and PO2<30 mTorr. The epitaxial NiO films obtained under these conditions have a good out-of-plane and in-plane orientation, with a full-width-half-maximum of about 6.5° and 9.5°, respectively. The in-plane epitaxial relationship is [1 0 0]NiO&par;[1 1 0]Ni–V. The as-obtained films have a compact and crack-free morphology, with grain sizes ranging from 30 to 300 nm. Nevertheless, the NiO films grown on (1 1 3) oriented grains or on twins are polycrystalline with a bright aspect, exhibiting a spongeous morphology. Epitaxial YBCO/CeO2/NiO/Ni–V structures grown on the NiO template have a critical current density of about 0.6 MA/cm2 at 77 K and zero magnetic field. [Copyright &y& Elsevier]