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A detailed study on YBa(2)Cu(3)O(7-delta) (YBCO) films with BaZrO(3) (BZO) inclusions (YBCO-BZO) deposited on SrTiO(3) substrate with different BZO contents is presented. X ray diffraction, SEM imaging and superconductive critical temperature (T(c)) measurements were performed to evaluate film growth quality. Independently from the BZO content, all YBCO-BZO films showed T(c) values close to that of pure YBCO indicating that the T(c) reduction which is usually observed on YBCO-BZO films can be successfully recovered by changing the deposition conditions. All YBCO-BZO films showed an improved critical current density (J(c)) dependence on magnetic field if compared to the typical J(c)(H) of YBCO, resulting in higher irreversibility fields up to 9 T at 77 K. SEM observation on etched samples suggests a direct link between the defect density measured in YBCO-BZO samples and that calculated from the observed in field performances. The analysis of J(c)(B) as a function of applied magnetic field direction revealed that the pinning due to isotropic pinning centers typical for YBCO is coupled with a c-axis correlated pinning in YBCO-BZO which can be ascribed to BZO induced columnar defects. J(c)(B) recorded at several temperatures down to 10 K revealed matching effect features.

We perform measurements of high-frequency (similar to 48 GHz) microwave surface impedance with an applied magnetic field in YBa(2)Cu(3)O(7-delta) ( YBCO) laser-ablated films with various amounts of BaZrO(3) ( BZO) sub-micrometric inclusions, up to 7 mol % concentration. BZO inclusions are very effective in the reduction of the field-induced surface resistance in our experimentally accessible field range [ 0, 0.8] T. At temperatures low enough, the application of a moderate (similar to 0.2 T) field makes the YBCO/BZO films markedly less dissipative than pure YBCO. This result, examined in the light of the very high measuring frequency ( very small vortex oscillation amplitude) shows that BZO inclusions are even more effective pinning centers than columnar defects. We study the dependence of the vortex parameters ( vortex viscosity, pinning constant) on the BZO concentration. We examine the correlation between the reduction of the microwave dissipation and the areal density of BZO-induced defects. We argue that the very improved performances in a magnetic field are due to individual pinning of vortices on BZO inclusions.

The addition of artificially induced defects improves the pinning efficiency of magnetic flux vortices in YBa2Cu3O7-delta (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 I mu m. 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. De electrical transport measurements at 77 K have revealed a better magnetic field retention of the critical current density, J(c) 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.

The introduction of artificial pinning sites in YBa(2)Cu(3)O(7-delta) (YBCO) epitaxial thin films has been obtained by pulsed laser deposition (PLD) technique from YBCO-BaZrO(3) (BZO) composite targets with BZO concentration ranging from 2.5 to 7 mol %. The typical critical temperature, T(c), drop observed in YBCO-secondary phase films grown by PLD has been successfully recovered by increasing the deposition temperature. Transport properties analyses revealed improved pinning force values for YBCO-BZO films for BZO concentration above 5 mol %. These films exhibited an anomalous dual peak structure which has been ascribed to the presence of two pinning contributions. The crossover field, B(m), separating these two pinning regimes has been observed to be temperature independent suggesting the occurrence of the matching field effect. The measured value of B(m) agreed with the matching field value, B(Phi)=Kn(d)Phi(0), as evaluated from transmission electron microscopy investigations. The mark of this phenomenon is retained down to 10 K, making YBCO-BZO more performing than pristine YBCO films at applied magnetic fields below B(m) in all the temperature range inspected. On the contrary, in the high magnetic field range (above B(m)), the effectiveness of correlated pinning is progressively reduced on lowering the temperature suggesting that at low temperatures the dominant pinning contribution arises from isotropic pinning centers. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3477451]

In this contribution, we report on the study of the vortex pinning properties of YBa 2 Cu 3 O 7-δ (YBCO) film grown on decorated substrate to obtain an improvement of magnetic field dependence of the critical current. Surface-decorated SrTiO 3 (STO) substrates have been obtained by polymer assisted deposition (PAD) with BaZrO 3 (BZO) nanoislands uniformly distributed over the substrate surface. Thanks to the high density of the polymer, the viscosity of the solution can be easily adjusted to tune nanoislands' density. Typical values of nanoislands' diameter and height are around 20-50 and 3-5 nm, respectively. YBCO films, derived by metal-organic decomposition (MOD) using low-fluorine precursor solution, were successfully grown on both bare and BZO-decorated STO substrate. Results indicated that surface decoration is effective to enhance pinning at both 77 and 65 K in the whole field range up to 7 T. As a matter of fact, the value of critical current doubled with respect to YBCO film grown on bare STO at 77 K and 1 T. © 2002-2011 IEEE