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A new modified TFA-MOD method for the YBa2Cu3O7-x (YBCO) deposition, using only barium trifluoroacetate, is presented. The yttrium and copper trifluoroacetates were replaced by the alcoholic solutions of Cu and Y acetates dispersed in propionic acid to prepare a stable coating solution. Due to the smaller amount of evolved hydrofluoric acid, this method permits the shortening of the pyrolysis time by a factor 4, with respect to conventional trifluoroacetate metal organic deposition (TFA-MOD) method. The X-ray photoelectron spectroscopy (XPS) analyses, performed on a pyrolyzed sample, showed the complete decomposition of precursors. The as obtained films exhibit good morphological, structural and superconducting properties with Tc(R = 0) greater than 90 K. Transport measurements at different temperatures and applied magnetic fields have revealed promising superconducting properties of the critical current density (Jc) vs. the applied magnetic fields and the value of Jc at 77 K and zero magnetic field greater than 3 MA/cm2.

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 10 at.% Ca substituted YBCO grown on CeO2 buffered Al2O3 single crystal substrates. Results are compared with data obtained on 10 at.% Ca substituted YBCO grown on SrTiO3 single crystal substrate. (c) 2005 Elsevier B.V. All rights reserved.

A new lanthanum and manganese ethylenediaminetetraacetate (EDTA) coordination polymer (EDTA4&minus, = [(CH2N)2(CH2-COOH)(CH2COO)4]) was synthesized from La(NO3)3 and Mn(NO3)2 reagents, ethylenediaminetetraacetic acid, and water at room temperature. The structure of the new compound formed, [{La2Mn3(EDTA)3(H2O)11}&middot, 12H2O]n, was determined by the single crystal X-ray diffraction technique. The synthesis and characterization of the La(III) and Mn(II) coordination complex, characterized by FTIR spectroscopy, thermogravimetry, and differential thermal analysis of the complex, are envisaged. X-ray crystal structure determination indicates that seven- and four-coordinate modes between La(III)/Mn(&Pi, ) and H4EDTA exist. [{La2Mn3(EDTA)3(H2O)11}&middot, 12H2O]n crystallizes in the monoclinic space group C2 with unit cell parameters of a = 16.1227(17) &Aring, b = 14.8049(16) &Aring, c = 14.8736(16) &Aring, and &beta, = 116.107(2)&deg, Using this precursor, LaMnO3 (LMO) epitaxial thin films were grown by the polymer-assisted deposition (PAD) method on (100)SrTiO3 (STO) single crystalline substrates at a temperature of 900 &deg, C. The LMO crystallized films exhibit a (001)LMO/(001)STO out-of-plane epitaxial relationship and a smooth surface morphology.

The transport properties of nanocomposite YBa 2 Cu 3 O 7-x (YBCO) films grown by metal-organic decomposition (MOD) and prepared with a low-fluorine-coating solution on SrTiO 3 single-crystal substrates were studied with dc and microwave measurement techniques. As demonstrated in previous studies, the combination of these two techniques is a powerful tool for vortex pinning investigation. The BaZrO 3 inclusions (BZO) as artificial pinning centers were introduced into the YBCO matrix by the excess of corresponding Ba and Zr precursor salts to the initial YBCO precursor solution up to 5 mol%. The effect of BZO was clearly observed in magnetic field dependence relations of critical current density (J c ) and the complex surface impedance, i.e., ΔZ, at fixed temperature and magnetic field parallel to the c-axis. The result shows that BZO particles mainly act as isotropic pinning centers. The short-range vortex dynamics was probed by the ~47.7-GHz microwave surface impedance technique. The derived vortex parameters r and k p were sensitive to the presence of nanoparticles, indicating the effect of BZO on pinning. The joint field dependence relations of J c and k p help in elucidating the pinning regime in our nanocomposite MOD YBCO/BZO films.

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.