YBCO Powder Research Articles

The direct evaluation of the internal strain of biaxially textured YBCO film in a coatedconductor using synchrotron radiation

The internal strain state of the superconducting film in a coated conductorshould be clarified to understand the strain effect on the critical current(Ic). We have developed an in situ strain measurement technique using synchrotron radiation forYBa2Cu3O7−δ (YBCO) coated conductor, and the internal strain of the YBCO film was directlyevaluated. YBCO powder obtained from the film in the coated conductor was used as areference of the zero-strain state. Shifts of the Bragg peaks of the (020) plane of the YBCOfilm were measured under applied tensile strain, and the internal strain was calculated fromthe change in the interplanar spacing. The residual strain of the YBCO film inthis coated conductor at room temperature (RT) was directly determined to be−0.061%. The fracture strain of the YBCO film was also evaluated from the relationship betweenthe applied strain and the internal strain of YBCO. Surface observation of the coatedconductor suggests that fracture initiates in the MgO buffer layer. The irreversible strain(εirr) determinedby Ic–strain characteristics at 77 K was compared with the result from in situ strainmeasurement. The validity of our technique using synchrotron radiation is discussed.

The study on various wet chemistry techniques on YBa 2Cu 3O 7−δ superconducting oxides powder preparation

This paper reports on the results of four different wet chemical techniques used for the synthesis of superconducting oxides, YBa 2Cu 3O 7 (YBCO). YBCO samples were prepared by complexion citric gel route (CT), acetate–tartrate sol–gel (ASG), oxalate/ethanol coprecipitation (COP), and acetate–tartrate sol–gel solid-state reaction (ASG-SSR) techniques. Each of the YBCO powders was annealed for 4 h at 880 °C, 900 °C, 920 °C, and 950 °C to find the optimum temperature. The optimum sintering temperature for the formation of Y-123 phase is very much dependent on the type of wet chemical technique used to prepare the powders.

Magnetic response of superconducting mesoscopic-size YBCO powder

In this work it is reported the magnetic behavior of submicron and mesoscopic-size superconducting YBCO powders, prepared by a modified polymeric precursors method. The grain size and microstructure were analyzed using scanning electron microscopy (SEM). Measurements of magnetization and AC-susceptibility as a function of temperature were performed with a quantum design SQUID magnetometer. Our results indicated significant differences on the magnetic propreties, in connection with the calcination temperature and the pressure used to pelletize the samples. This contribution is part of an effort to study vortex dynamics and magnetic properties of submicron and mesoscopic-size superconducting samples.

Using non-fluorine precursor to prepare YBCO thin films by chemical solution deposition

A fluorine-free chemical solution deposition route has been established for YBCO thin films which is inexpensive and environmentally friendly. The YBCO precursor was formed by dissolving the YBCO powder in organic acid and polymer. Amine is used to modify the solution. Several routes with different reagents have been investigated. For the preparation of YBCO thin films, a thin precursor film was coated on single crystal substrate by dip-coating and burnt out on a hotplate in air followed by annealing in a tube furnace with low oxygen pressure argon atmosphere. The films have been characterised by XRD and SEM and the superconducting properties measured by AC susceptibility. The effect of annealing temperature and oxygen partial pressure has been studied.

The effect of BaCeO3 nano particles on the current density of a melt-processed YBCO superconductor

The effect of BaCeO3 addition on the microstructure and the critical current density of a melt-textured YBa2Cu3O7−y sample has been investigated. The BaCeO3 powder was prepared by a conventional solid-state reaction method and the size was reduced by attrition milling. The BaCeO3 powders with various contents (3, 5, 10, 15, 20wt.%) were mixed with YBCO (Y123 composition) powder and then melt-textured. It was found that the BaCeO3 particles with a cubic shape were trapped in the Y123 grains. The distribution of BaCeO3 particles inside 123 grains was not uniform due to the formation and of the particle free regions and the segregation in local parts. The particle segregation tends to be more serious when the particle is finer. The critical current density (Jc) at 77K of the sample with much BaCeO3 addition was higher than that of the sample with a small addition.

超電導バルク体製造における粉体圧縮時の成形体欠陥

In the production of melt-textured RE-Ba-Cu-O bulk superconductors, the precursors are generally prepared by uniaxial and/or cold-isostatic pressing of raw powders. The employment of fine starting powders is effective in fabricating high-performance RE-Ba-Cu-O bulk superconductors. However, cracks often form in the green bodies when fine powders are unaxially pressed. In this work, we have investigated the defects in green bodies during the powder compression process for bulk superconductor fabrication. Fine and large YBCO powders and granulates of binder-added fine powder were uniaxially pressed into tablets (20 mm in diameter) using different pressures from 31 to 125 MPa. When the fine powder was pressed at pressures above 62 MPa, several defects such as lamination, capping and cracks on the parallel in the direction of pressing were found in green bodies. These defects in green bodies partially remained after melt-processing and affected the field-trapping abilities of melt-textured bulk samples. The addition of an organic binder is very effective method for reducing defects in green bodies.

Anisotropic effects in a powder oriented YBCO sample using a three axes magnetometer

AbstractTo measure the components of the magnetization vector along the XYZ directions of a reference frame, in the superconducting materials, we have conceived a three axes magnetometer, with a detection system equipped with three series of pick‐up coils with axes parallel to the three directions X,Y, and Z. We describe in this paper the details of the design and the method of measurement, with some results obtained by magnetic measurements on samples of oriented YBCO powder, with size of the grains between 20 µm and 40 µm, for values of the angle θ between the magnetic field H and the c‐axis, between 0° and 90° and for values of fields up to 12 T. The direct measurement of the Z and the XY components of the irreversible magnetization vector, Mirr, allowed us to observe the twin effect (channeling) on the vortex pinning observed by many authors, the evolution of the magnetization vector and to measure with a high accuracy the anisotropy factor of our samples. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The flux pinning enhancement of YBCO film prepared by PLD using composite targets doped with BaZrO3 nanopowder

BaZrO3 nanopowder was added to YBCO powder to make (BaZrO3)x(YBCO)(100−x)mol.% (BZOx-YBCO) (0⩽x⩽10) composite targets for pulsed laser deposition of superconducting film in order to investigate the effect of the addition of BZO nanopowder in the YBCO target on the flux pinning properties of YBCO coated conductor. All the BZOx-YBCO films were grown on SrTiO3 single crystal substrate under the same conditions in the PLD chamber. The effect of adding BZO to YBCO targets on the flux pinning properties of BZOx-YBCO films has been investigated. No impurity phase was identified, and all the peaks could be indexed as YBCO, BZO, and STO. There were traces of strong pinning centers at low temperature and high magnetic field region (above ∼3T) in BZO6-YBCO film with the addition of ∼6mol.% BZO nanopowder. However, the Tc of the BZOx-YBCO films gradually decreased as the amount of BZO nanopowder added increased.

Fabrication of High-<tex>$Jrm c$</tex>YBCO Films by the TFA-MOD Process Using YBCO Powder as Precursor

YBCO thin films were prepared on LaAlO/sub 3/ (100) single-crystal substrates using the metal-organic deposition of trifluoroacetates (TFA-MOD). Unlike the normal TFA-MOD process, TFA-based solutions were prepared dissolving YBCO powder into the trifluoroacetic acid solvent. The solutions were coated on the substrates by spin coating, fired at the temperature up to 400/spl deg/C in 4.2% humid and oxygen atmosphere, fired again at the temperature region of 725-850/spl deg/C for 2 h in 4.2% humidity and 1000 ppm oxygen partial pressure, and finally oxygenated at 450/spl deg/C for 1 h. Similar to the normal TFA-MOD process, both microstructure and superconducting properties of YBCO films were highly sensitive to the firing temperature. Optimally processed YBCO films of /spl sim/250 nm thickness exhibited T/sub C,zero/ of 90 K and J/sub C/ of 2.9 MA/cm/sup 2/ at 77 K in a self-field. The present results clearly evidence that our cost-effective modified TFA-MOD process is applicable to the fabrication of YBCO coated conductors.

Texture of YBCO/Ag PIT-tapes

YBCO/Ag tapes prepared using nanosized YBCO powder are currently the best powder-in-tube YBCO tapes with their I c=5.02 A and J c=3300 A/cm 2 in self-field and at 77 K. The texture of these tapes was studied by removing the silver with mercury and then measuring the texture of the surface with X-ray diffraction. A clear correlation between I c and c-axis texture is found and even some evidence of ab-texturing in the very best tapes. Less texture is found when the middle of the filament is exposed by cutting the tape. This suggests that multifilament tapes with smaller filament cross-section should have even higher I c.

New chemical route for YBCO thin films

Sol-gel derived coating of YBCO film is very attractive for low cost as well as the ease of scalability. Among them, TFA-MOD using metal trifluoroacetates helps avoid the formation of BaCO/sub 3/ in the film. But this process has difficulties in optimizing the humid atmosphere to remove HF from the Y-Ba-Cu-O-F systems. So, in this work, another approach to chemical solution without fluorinated precursor was investigated. To make homogeneous stable solution, at first, YBCO powders were synthesized from organic solution containing Y/sub 2/O/sub 3/, BaCO/sub 3/, and CuO powders followed by calcination in air. Dip coatings were carried out from the solution of calcined YBCO powder dissolved into a mixture of methanol and propionic acid on LaAlO/sub 3/ [100] substrates. The coated film was annealed by reduced oxygen partial pressure. Dense, homogeneous and biepitaxially grown YBCO films were obtained from dip coating with /spl sim/5 mm/s of drawing speed.

Comparison of the oxalate co-precipitation and the solid state reaction methods for the production of high temperature superconducting powders and coatings

High quality orientated YBa 2Cu 3O 7− x ( x=0.1–0.2) (YBCO) superconducting coatings were produced by the electrophoretic deposition technique. The fine particle YBCO powder used, was produced by the oxalate co-precipitation method on Au/Si and Pt/Si wafers. The optimized thermal treatment for both, powders and coatings, was followed by thermal analysis (thermogravimetry (TG) and differential scanning calorimetry (DSC)). The powders and coatings obtained, were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), optical microscopy, magnetic susceptibility and electrical resistivity measurements. It resulted that by the oxalate co-precipitation method finer and more homogeneous nanocrystalline YBCO powders were produced in comparison to the solid state reaction method, leading to more favorable conditions for their thermal treatment, like lower sintering temperature and shorter duration of the sintering process, as well as better superconducting properties, expressed by the shape and value of the corresponding magnetization curves. Furthermore, the production of the coatings was achieved in a shorter electrophoresis time by the powders from the co-precipitation method and the coatings produced were orientated having improved superconducting properties in comparison to those obtained by the solid state reaction method.

Superconducting YBCO/Ag composite films prepared by spraying a suspension

YBCO films of approximately 7–8-μm thickness on YSZ substrate were fabricated by spraying a suspension consisting of YBCO powders. The film with 10 wt.% Ag fired at 920°C showed relatively high Jc values of approximately 3.3×103 Acm−2 (77 K, 0 T) as compared to approximately 1.0×103 Acm−2 for the undoped films.

Uranium fission fragment pinning centers in melt-textured YBCO

In the U/n process YBCO powders are doped with uranium, textured, and then irradiated with thermal neutrons. During texturing almost spherical deposits of (U 0.6Pt 0.4)YBa 2O 6 (called Y-5), 300nm in diameter, are formed. Prior to irradiation Y-5 deposits increase J c about 10% 0.1% M U, where M U is the percentage by weight of admixed uranium which contains an intimate mixture of both the 235U and the 238U isotopes. We find the number of Y-5 deposits ∝ M U. Hence, inter-deposit spacing, S ∝ M U −1 3 . Subsequent irradiation with thermal neutrons produces fission fragment defects that also act as pinning centers. The effective length for pinning, δ, of these pinning centers was estimated theoretically to be 2μm to 4μm. The effect of the chemical and irradiation pinning centers is multiplicative and increase J c, depending on applied field and temperature, by factors of 14 to 40. The value of F n at which J c peaks depends only on the product of F n and M U(235), where F n is the numberof neutrons per square centimeter. We find that optimum F n is inversely proportional to M U(235). M U was varied from 0.0375% to 1.0%, with M U(235) held constant at 0.025%, thus varying S by a factor of 3. The enhancement of trapped field, R M, is 500% at 0.15%<M U<0.30% and drops to 400% for o.375% M U, indicating δ ∼ 2.7 μm. Anisotropy of (3mm) 3 samples decreases monotonically from 3 to 2 with increasing F n. Residual radioactivity six months after irradiation is <200 nCi/g or <7400 Bq/g for samples with 0.025% M U(235) at optimum F n.

Preparation of YBCO superconducting thick film by electrophoresis

The thick films of YBa 2Cu 3O x (YBCO) superconductor were prepared by electrophoretic deposition, using pre-sintered YBCO powder dispersed in acetone solution. The alumina (Al 2O 3) ceramic plate, coated with Ag, was used as the cathode substrate and the stainless steel mesh electrode was used as the counter electrode in suspension for electrophoresis. The conditions of applied voltages and temperatures, contents of iodine additives, and deposition times for electrophoretic deposition of YBCO thick films were studied in detail. As a result, the optimum value of iodine content in acetone was 200 mg/l, the applied electrical potential for electrophoresis was 200–300 V for 10 mm electrode gap, and the content of YBCO powder was 10–20 g/l in acetone suspension solution. The critical temperature was determined at 91 K by AC susceptibility curve and the critical current density, J c, was measured by a four-point prove method at the value of 700 A/cm 2 deposited on the Ag coated Al 2O 3 substrate and 1456 A/cm 2 deposited on the Ag wire (77 K, 0 T).

Investigation of glass behaviour of vortex arrays in superconducting submicron YBCO powders by magnetic relaxation measurements

Magnetic relaxation measurements are made in the remanent state of pure and Zn-doped submicron YBCO powders. A characteristic feature of these samples is dipolar interaction between single vortices trapped in different particles. Similar to other systems with dipolar interactions, such as powders of fine ferromagnetic particles, our samples show glassy behaviour: different metastable states with various pinning properties can be prepared by varying the strength of the magnetizing field, i.e. history of the sample. It is found also that the relation between the pinning energy and the magnetic moment can be described by an expression similar to the vortex glass interpolation formula.

YBCO films on nickel alloy substrates prepared by spray deposition technique

YBCO films of about 70–80 μm thickness on Inconel 600, Inconel X and Hastelloy substrates were fabricated by spraying a suspension consisting of YBCO powders. The films on Inconel 600 which were fired at 910°C in flowing argon and then annealed in oxygen showed relatively high J c value of about 400 A cm −2 at 77 K in zero magnetic field. Only the films fired at 910°C and 920°C attained zero resistivity above 77 K.

YBCO films on nickel substrates prepared by spraying a suspension

Y1Ba2Cu3Ox films of about 50–60 μm thickness on Ni substrates were fabricated by spraying a suspension consisting of YBCO powders. The films which were fired under flowing argon and then annealed in oxygen showed relatively high Jc values of about 500 A/cm2 (77 K, 0T) over a firing temperature range from 910–950°C. When the films were fired at 960°C, the Ni whose concentration was about 4 at.% and large-size cracks were found to be present on the surface of the film, resulting in the destruction of the superconducting properties of the film. The reaction products produced near the interface regions and on the surface of the films were also studied.

Influence of surface doping on sintering and microstructure of a superconducting oxide

The influence of surface halogen doping on the sintering and microstructure of Y 1Ba 2Cu 3O 7− x (YBCO) has been investigated. It is seen that exposing the starting YBCO powder to Br gas prior to sintering results in secondary recrystallization and formation of long columnar grains. The chemical composition and structure of the overall material is unchanged indicating that it is only the microstructure that is effected by the bromine. Since large domain sizes and preferred orientations are key to electrical and levitation properties of these materials, this effect of increased grain growth may prove to be very useful in controlling the texture of these materials. Even in randomly mixed composites of Ag and YBCO, Br is seen to increase the grain size and porosity of the YBCO regions, indicating that grain growth outpaces pore elimination. It is likely that Br, as a surface additive, enhances liquid phase formation and/or increased diffusion at the interfaces that lead to these effects. The atomistic mechanism of the process and the quantitative optimization of the doping concentration need to be investigated.

Properties of sprayed YBCO films on YSZ substrates

Y 1Ba 2Cu 3O x films, ranging in thickness from 1.5 to 7.5 μm, on (100) YSZ substrates were fabricated by spraying a suspension consisting of YBCO powders. The films were sintered at 940°C for 2 min under flowing argon and then exposed to oxygen. It was found that the spraying conditions such as the flow rate of carrier gas and the aperture of spray nozzle had a great influence on both the mechanical and the superconducting properties of YBCO films. The maximum critical current density J c (77 K) of about 4200 A cm − 2 was obtained by reducing the droplet size.