The structure and dynamics of magnetic vortices in high-Tc superconductors are studied. The model we use is applicable to highly anisotropic high-Tc superconductors, such as Bi and Th compounds, where the Josephson coupling is neglected between the superconducting layers. In this paper, we studied the ac losses occurring in a finite number of superconducting layers due to an applied ac current. It is found that the ac losses increase with the frequency and the amplitude of the applied current. By introducing random pinning centers in the layers, the effect of pinning on the reduction of ac losses is also studied.

High quality thin films of HTS have been grown by MOCVD on substrates with artificial steps of predefined height and width. The surface of the films grown on the steps having width equal to the ‘double of the migration length' of the atomic species depositing on the substrate is totally free of precipitates: precipitates are gathered at the step edges where the free energy is lowest. The method has several advantages: it is simple, universal (it is independent of the materials, substrates, deposition technique or application) and allows control of precipitates segregates so that the quality and growth conditions of the films are the same as for the films grown on conventional substrates. The method is expected to result in new opportunities for the device fabrication, design and performance. As an example we present successful fabrication of a mesa structure showing intrinsic Josephson effect. We have used thin films of Bi-2212/Bi-2223 superstructure grown on (001) SrTiO3 single crystal substrates with artificial steps of 20 μm.

Electrodeposition (ED) is a potentially low-cost, non-vacuum, high-rate deposition process that can easily deposit uniform film on large non-planar substrates. In this paper, we report on successful biaxial textured electrodeposition of Ir on Ni-W substrates. Ir metal is well known for its excellent oxidation and corrosion resistance among platinumgroup elements; also, the lattice mismatch of cubic Ir is very close to that of CeO2 and Ni. The films were deposited in a vertical cell in which the electrodes (both working and counter) were suspended vertically from the top of the cell. The ED experiments were performed at 65°C without stirring the solution. The ED precursors were prepared at about -1.2 V from 2 to 15 minutes on Ni-W, where the Pt counter and Pt pseudo-reference electrodes were shorted together. To qualify the electrodeposited Ir buffer layer, a CeO2/YSZ/CeO2 and YSZ/CeO2 buffer structure was later deposited on ED Ir-coated Ni-W substrates by pulsed-laser deposition. The ED Ir/metal substrates were first heated at 800°C in 0.5 mTorr of forming gas, and then a CeO2 seed layer was deposited in 180 mTorr of forming gas. Subsequently, YSZ and CeO2 layers were deposited sequentially in 0.1 mTorr of oxygen.

Over current stabilization of YBa2Cu30x (YBCO) coated conductor high temperature superconductor tape is required in most applications. The conductor must carry currents in excess of the critical current, Ic, without damage during over current events. Conductor damage is the result of joule heating and excessive temperature rise in regions with low Ic. We have developed and applied a measurement technique using a locally applied magnetic field with a high spatial gradient to define a small area over which the Ic is depressed. By measuring the voltage and temperature as a function of current, power dissipation and temperature rise were determined. Unstabilized conductors experienced thermal runaway and are easily damaged. Copper stabilizers applied by electroplating decreased dramatically the temperature rise and increased the level of power dissipation compared with the unstabilized conductor.

Nonvacuum electrodeposition was used to prepare biaxially textured CeO2 and Sm-doped CeO2 coatings on Ni-W substrates. The samples were characterized by X-ray diffraction (including Θ/2Θ, pole figures, omega scans, and phi scans), atomic force microscopy, and Auger electron spectroscopy (AES). Pole-figure scans show that electrodeposited CeO2 and Sm-doped CeO2 on textured Ni-W (3 at.%) is cube textured. Full-width at half-maximum values of thew scan andf scan of the electrodeposited layers were better than those of the Ni-W base substrates, indicating improved biaxial texturing of the electrodeposited layers. AES analysis of the YBCO/CeO2/YSZ/ED-CeO2/Ni-W revealed that Ni interdiffusion was completely stopped at the first electrodeposited CeO2 layer.

We have grown epitaxial rare earth niobate (RE3NbO7; RE – La, Ce, Nd, Sm, Eu, Gd, Ho, Y, and Yb) buffer layers on biaxially textured Ni-W substrates using chemical solution deposition approach. Precursor solutions of 0.4 M total cation concentration were spin coated on short samples of Ni-3 at.%W (Ni-W) substrates and heat-treated at 1050 to 1100°C in a gas mixture of Ar-4%H2 for 15 minutes. Effect of solution chemistry and processing atmosphere on texture and microstructure were studied. Detailed X-Ray studies indicated that all the rare earth niobates were grown epitaxially. There was no significant change observed in texture for different precursor chemistry, however, dramatic effect on surface morphology observed. SEM and AFM investigations of RE3NbO7 films reveal noticeable difference in surface morphology and roughness for various processing atmospheres. Processing under a 20% wet Ar-4% H2 gas mixture was found to be the optimum condition for growing Gd3NbO7 films with high quality microstructure.

Ceria nanoparticles were prepared using a solution based approach using cerium (III) acetate as a starting material and cetyltrimethylammonium hydroxide (CTAOH) as a precipitating agent and surfactant. The presence of the surfactant CTAOH helps prevent agglomeration of the nanoparticles. Using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM), the particle size was determined to be 3.5 – 4 nm. The structure and properties of these CeO2 nanoparticles have been analyzed.

We present a comparative study in terms of structural properties deduced from X - ray diffraction diagrams between YBa2Cu3O7 (YBCO) thin films fabricated on SrTiO3 (STO) single crystal substrates and bicrystallines substrates with a symmetrical tilt angle of 24 degrees. Periodic Lattice Distortions (PLD) have been observed around different Bragg peaks in YBCO thin films deposited on STO bicrystals while only diffraction peaks have been measured in the diagrams corresponding to the YBCO thin films deposited on STO single crystal substrates. Only in regions situated a 3.5 mm at both sides of the grain boundary the PDL have been investigated. Scans along different (h, k, l) directions allow us to conclude that the qPLD vector associated to the distortion is along the (h,-k,0) direction. However, we found that the amplitude of the components of the qPLD vector depend on the Bragg peak chosen. We believe such a result indicates that we have not a PDL with a simple qPLD vector. In this line, other (h, k, l) directions must be investigated to deduce the exact origin of the qPLD vector. Nevertheless, independently on the qPLD vector associated to the PLD, we believe that such a distortion in the lattice is a consequence of the stress field induced by the grain boundary in the YBCO thin film deposited on the bricrystal.

The evolution from a partially oriented granular microstructure to a dense epitaxial one in CeO2 buffer layers deposited by metallorganic decomposition (MOD) on single crystal Y-stabilised ZrO2 (YSZ) substrates, has been investigated. CeO2 buffer layers were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), reflection high energy electron diffraction (RHEED), transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Reducing atmospheric conditions inhibit grain growth resulting in a nanometric granular microstructure with a high concentration of C impurities decorating grain boundaries and porosity. Oxidation and elimination of C species promotes grain growth resulting in a dense epitaxial film, as well as stabilizes otherwise energetically prohibitive polar (001) planes. Trifluoracetate (TFA) derived MOD YBa2Cu3O7 (YBCO) films deposited on optimized CeO2 buffers exhibit a sharp interface while the undesired reaction giving BaCeO3 is minimized. Jc values of 1.5 MA/cm2 and 14 MA/cm2 at 77K and 5K, respectively, are achieved.

Iridium film is a potential candidate as a buffer layer for yttrium barium copper oxide (YBCO) coated conductors. Pulsed laser deposition (PLD) of biaxially textured CeO2/yttrium stabilized zirconium oxide (YSZ) layers on electrodeposited Ir/Ni-W is reported. Biaxial texturing is obtained by deposition of a YSZ seed layer at 800°C in 10-6 Torr vacuum. X-ray diffraction (XRD) studies of Θ-2Θ and pole figure confirmed in-plane out-of-plane biaxial texturing with Δφ = 6.5° and Δω = 8°. Atomic force microscopy (AFM) revealed a surface with roughness of about 3 nm.

Our multi-plume and multi-turn (MPT) pulsed-laser deposition (PLD) has been improved to accelerate reliable and fast deposition technique of high Ic (critical current) YBCO (YBa2Cu3O7-x) layer for a long coated conductor fabrication, for we increased the number of multi-turn, from three to four, in our multi-plume and multi-turn (MPT) PLD system. This increase of the number of depositing turns achieved high deposition rate corresponded to 75 mm3/h (=1 μm-thick × 10 mm-wide × 7.5 m/h, throughout all 4 turns) for YBCO layer. This four turn (4t)-MPT-PLD also indicated a capability to combine high deposition rate and high Ic. We attained the highest Ic's of 321 A at the tape speed of 3 m/h and 340 A at tape speed of 2 m/h by 4t-MPT-PLD in 10 mm-wide and 10 cm-long samples.

Based on these results, we successfully deposited a 100 m long YBCO layer by 4t-MPT-PLD. This coated conductor had high Ic as high as 159 A, therefore, the multiplication of Ic and length exhibited high value of 15.9 kA·m.

The variation in the substrate temperature during ion beam assisted deposition (IBAD), which employs the use of energetic ions to bombard a growing film, has been shown to influence the quality of crystalline texture in MgO films. Determining the acceptable deviation from the optimum ion to molecule ratio for different substrate temperatures establishes the optimum MgO deposition conditions. For each fixed deposition temperature, a set of samples was produced by varying the ion assist beam current from sample to sample while keeping the deposition rate constant. In this way, the ion to molecule ratio was modified and the range of achieving well textured films was determined. The investigation of the MgO texture dependence on the substrate temperature reveals that the best in-plane alignment is obtained at ˜ 25°C. At this temperature, MgO films with in-plane orientation distribution as low as 3.7° full width at half maximum (FWHM) have been attained. MgO films deposited at temperatures higher than 100°C have broad in-plane alignment. Although, the deposition at the lowest temperature (-150°C) did not improve the in-plane texture, the acceptable deviation from the optimum ion to molecule ratio for achieving biaxially textured films was the largest. As a trend, the acceptable ion to molecule deviation decreases with increasing substrate temperature. This is especially important for continuous IBAD MgO depositions where less restrictive conditions are desired.

We prepared REBa2Cu3O7- δ (RE= Gd, Sm, Dy, Er, Y) coated conductors on pulsed laser deposition (PLD) -CeO2/ion-beam assisted deposition (IBAD) – Gd2Zr2O7 (GZO) / metal tapes by the PLD method and measured the characteristics in magnetic fields. The GdBa2Cu3O7- σ (Gd-123) films showed superior characteristics than others in magnetic fields and showed weak anisotropy. Critical current density (Jc) value of the Gd-123 film was 3.87MA/cm2 at self-field and 0.19MA/cm2 at 3 T of perpendicular field to the tape surface in liquid nitrogen (77 K). Angular dependences in magnetic fields (Jc -Θ) of the Gd-123 and the SmBa2Cu3O7- σ (Sm-123) were superior to others and peaks in Jc -Θ were found also at 0 degree. The reduction ratios of Jc in Jc -Θ for the Gd-123 film and the Sm-123 film were smaller than other films. Transmission electron microscopy showed that the Gd-123 film had many stacking faults. It may be considered that this stacking faults naturally introduced by the PLD method contribute to improvement of anisotropy of Jc -Θ in the Gd-123 film.

Biaxially textured YBa2Cu307-δ films were fabricated by non-vacuum electrodeposition and spray pyrolysis techniques. Electrodeposited YBCO was prepared on sputtered copper/single-crystal substrates. Electrodeposition was carried out at constant voltage and the deposition was completed in only few minutes. The thickness of the as-deposited films was in the range of 0.6 to 2 μm. The optimized sputtered copper layer thickness was about 200 Å on SrTiO3. In the spray pyrolysis method, the solution is sprayed directly onto SrTiO3 substrates. The substrate temperature is about 100°C. The thickness of the as-deposited films was in the range of 1.2 to 2μm. The electrodeposited and spray-deposited films were annealed at temperatures ranging from 800° to 920°C under various flowing gas mixtures. X-ray diffraction analysis revealed that processed electrodeposited and spray-deposited films were biaxially textured, where YBCO grains were well oriented along the c-axis and in the (a,b) plane. Δω, deduced from the rocking curve on the (005) reflection, was as low as 0.46°. Δφ, deduced from the phi-scan on the (103) reflection, was as low as 0.54°. The critical current density for these types of films is about 0.5 MA/cm2at 77 K and 0 T.

In this work we will report our recent progress in the control of the interface quality between buffer layers and YBCO thin films grown by the trifluoroacetates route (TFA) and how it influences the critical current of the coated conductors. We have mainly focused on vacuum and metalorganic deposited (MOD) fluorite-like CeO2 buffer layers and on MOD perovskite SrTiO3 buffer layers. We will show that for vacuum CeO2 buffer layers, microcracks at the surface can be controlled by the means of thermal treatments. Coated conductors TFA-YBCO/CeO2sputt/YSZ/CeO2/Ni with Jc(77K)˜1MA/cm2 can be grown even in the presence of these microcracks. For MOD SrTiO3 we will show that growing the buffer layer at low temperature reduces surface roughness and multilayers with high critical currents can be achieved. An all-chemical coated conductor has been grown TFA-YBCO/SrTiO3MOD/BaZrO3MOD/NiO-SOE/Ni with promising in-plane texture, Δ φYBCO=6.6°. For MOD CeO2 buffer layers, thermal annealings in oxidizing atmospheres lead to atomically flat surfaces that avoid the typical polycrystalline surfaces observed in MOD CeO2 grown in Ar/H2. High Jc multilayers can be achieved and the first all chemical coated conductor in IBAD tapes TFA-YBCO/CeO2MOD/YSZIBAD/SS has been obtained with Jc(60K)=2.3MA/cm2.

Electron beam co-evaporation is one of the ex situ techniques being developed for cost-effective fabrication of YBa2Cu3O7-δ (YBCO) coated conductors. To achieve high critical current (Ic) and fast conversion, further understanding is needed of the chemical and microstructural characteristics of the precursors and the phase evolution process towards the epitaxial c-axis oriented YBCO film during the post-deposition conversion annealing. In this study, X-ray photoelectron spectroscopy (XPS) was used to investigate the chemical and compositional profiles of the precursors. Samples quenched from the processing stage were also inspected for identifying the transient elemental chemical states during the YBCO phase formation. XPS survey and detailed spectra were recorded for the surfaces and through various depths. It is suggested that XPS spectra, especially the “Auger parameters” can be used for revealing the conversion reaction. Preliminary results indicate that the copper oxidation state might have important effect on precursor conversion behaviors.

We successfully introduced high-density linear defects as artificial pinning centers (APCs) of the quantized vortices into YBCO films, during the film deposition procedure. APCs were introduced perpendicular to the film surface by using the distributed nano-sized Y2O3 islands prepared on SrTiO3(100) substrates. It is possible to induce strong changes on the shape and density of the Y2O3 islands by varying the deposition and annealing conditions. The highest Y2O3 islands density, 226/μm2, was obtained with fifteen laser pulses at 800°C of substrate temperature, and applying an annealing temperature of 800°C. Even if only a small fraction of the induced defects act as effective pinning centers, Jc of YBCO film grown on the Y2O3 nanoislands/SrTiO3 substrate increased to 1.8 107 A/cm2 (20 K, B//c, 0 T), which is 1.5 times higher than that of the pure YBCO film.