U. Gambardella

Properties of in-situ laser-pulsed deposited YBCO thin films on MgO with SrTiO3 buffer layer

Abstract Epitaxial YBa 2 Cu 3 O 7− y films were grown by pulsed-laser ablation on SrTiO 3 buffered (100) MgO substrate without any pre- or postannealing of the substrate or STO buffer layer. The role of the SrTiO 3 layer is to provide a better lattice mach to the YBCO film and to prevent the interaction between YBCO and MgO. The as-obtained YBCO films exhibit excellent structural and superconducting properties with T c (R = 0) = 90 K , R(300) R(100) = 2.8, Δ T = 0.8 K , J c ≈ 10 6 A/cm 2 (at 77 K and zero magnetic field) and a full width half maximum of the (005) YBCO peak of about 0.18°. These characteristics are very close to those of the YBCO film deposited on SrTiO 3 single crystal.

Biaxial texturing of Ni alloy substrates for YBCO coated conductors

Abstract Biaxial cube texturing and surface quality of the metallic substrate are key parameters for high J c coated conductors. Experiments have demonstrated that the sharp cube texture can be developed up to 11 at.% V, 12 at.% Cr and 5 at.% W alloys; the respective cube textured area fractions result to be 96%, 97% and 99%. For all the studied alloys, FWHM values of ω - and φ -scans are in the range of 5–6° and 6–8°, respectively. Microstructural analyses reveal smooth surfaces with grooves localized at the grain boundaries of twinned cube textured and misoriented grains.

Development of biaxially aligned buffer layers on Ni and Ni-based alloy substrates for YBCO tapes fabrication

This paper presents the development of the CeO/sub 2/ buffer layers on both the non magnetic Ni-V and the Pd-buffered Ni substrates by pulsed laser ablation (PLD). The CeO/sub 2/ films show strong in-plane and out-of-plane orientations. The SEM studies showed that the CeO/sub 2/ films are both smooth and continuous. The magnetic and structural properties of the new Ni-V substrate are also presented. The results demonstrate that Ni-V is an alternative substrate for the fabrication of textured YBCO conductors.

Epitaxial growth of YBa2Cu3O7-δ on Ni89V11 non-magnetic biaxially textured substrate using NiO as buffer layer

The superconducting YBa2Cu3O7-δ/CeO2/NiO multilayer structure was grown in situ by pulsed-laser deposition on biaxially textured Ni89V11 non-magnetic alloy. The role of vanadium is to decrease the Curie temperature of Ni and to favour the formation of oriented NiO. The (00l)NiO buffer layer has been formed by the controlled oxidation of the Ni-V substrate under 10 mTorr oxygen pressure and at 700 °C. The critical current density of 0.6 MA cm-2, at 77 K and zero magnetic field, was obtained for 0.7 µm thick YBa2Cu3O7-δ films.

High-quality surface YBCO thin films prepared by off-axis pulsed laser deposition technique

Abstract Epitaxial YBCO superconducting thin films have been grown in-situ by XeCl excimer laser ablation using an off-axis deposition geometry. This PLD geometry allows to obtain films with an excellent surface morphology without droplets or other particulates. The as-obtained YBCO films exhibit good structural and superconducting properties with T c( R = 0) =89.5 K, R (300) / R (100) =2.8, ΔT = 1.3 K, J c = 2 × 10 6 A/cm 2 (at 77 K and zero magnetic field) and full width half maximum of the rocking curve of the (005) YBCO peak of about 0.16°. These structural and electrical properties are very close to those of the YBCO films deposited by the conventional PLD on-axis geometry.

Cube-textured substrates for YBCO-coated conductors: microstructure evolution and stability

The realization of YBCO-based coated conductors with high critical current density involves the deposition of highly biaxially textured YBCO films. The use of epitaxial growth shifts this requirement to the template used for YBCO deposition. In the rolling-assisted biaxially textured substrate (RABiTS) approach, an appropriately oriented template is provided by a cube-textured substrate. The development of a cube texture is the result of recrystallization occurring in a heavily deformed tape, which is activated by high-temperature annealing. In the case of Ni-based alloys, thermal treatment at temperatures ranging from 900 to 1150??C for at least 30?min is commonly used. The determination of the minimum conditions for thermal treatments in terms of temperature?time involved in the recrystallization process is therefore of practical interest. In this work, Ni?5 at.% W alloy has been studied as a substrate for YBCO-coated conductors. 100??m thick tapes have been obtained through heavy cold rolling, followed by annealing in high vacuum. Different thermal treatments with rates of 20??C?min?1 have been performed in order to study the formation and the evolution of the cube texture. Moreover, the annealing time has been varied in order to inspect the thermal stability of the substrate microstructure at the relatively high deposition temperature of YBCO films. It is found that the substrate begins recrystallizing at 700??C and that the cube texture is fully developed at temperatures higher than 800??C, while annealing at 900??C for 1?h produces a stable microstructure at the typical YBCO deposition conditions.

Superconducting and structural properties of YBCO thick films grown on biaxially oriented CeO2/NiO/Ni-V architecture

Abstract Biaxially aligned YBa 2 Cu 3 O 7−y thick films were obtained by Pulsed Laser Deposition on cube textured non-magnetic Ni-V metallic substrates, with NiO as a first buffer layer. The critical temperature and critical current density at 77K and self field of the YBCO thick film grown on an epitaxial CeO 2 /NiO buffer layer architecture are 90.5K and 0.6 MA/cm 2 , respectively.

High-quality YBCO thin films grown by off-axis PLD geometry

In order to improve the surface quality of the pulsed laser deposited YBCO thin films an off-axis deposition geometiy is proposed. Using this new PLD geometry, YBCO thin films have been grown on SrTi03 substrates. These films were found to have a good surface morphology without droplets or other particulates, and good supelrconducting and structural properties. We have obtained Tc(R=0)=89 K, R(300)/R(100)=2.6, ΔT=1.5 K, Jc=2×106 A/cm2 (at 77 K and zero magnetic field), and the FWHM of the rocking curve of (005) YBCO peak is about 0.12°. A study regairding the influence of the deposition parameters on the film quality is also presented.

YBa 2 Cu 3 O 7−δ Films With BaZrO 3 Inclusions for Strong-Pinning in Superconducting Films on Single Crystal Substrate

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 1 mum. 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 < 1T). Very high depinning frequency are estimated in YBCO films with BZO inclusions indicating extremely high vortex pinning and steep potential wells.

Epitaxial oxidation of Ni-V biaxially textured tapes

Abstract The epitaxial oxidation of the (0xa00xa01)[1xa00xa00] 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: 700 ° C, t