H. Okuyucu

X-ray structure determination of the rare earth oxides (Er1−uGdu)2O3 applying the Rietveld method

Nanosized polycrystalline samples of (Er1−uGdu)2O3 (0 ≤ u ≤ 1.0) were synthesized by a sol–gel technique. X-ray diffraction data were collected and the crystal structures were refined by the Rietveld method. All samples are found to have the same crystal system and formed solid solutions over the whole range of u. The Er3+ and Gd3+ ions were randomly distributed over two cationic sites, 8b and 24d, in the space group Ia\bar{3} (206) in all refined structures. The lattice parameter was found to vary non-linearly with the composition (u). The average microstrain and average crystallite size have been calculated from the Williamson–Hall plots for each sample. The average size ranges from 50 to 70 nm, and the microstrain from 0.4 to 1.7%.

Electrical characterization of ceramic insulation coatings for magnet technology

In this study, electrical characterization of ceramic insulation coatings were evaluated by resistive, capacitance, and high voltage breakdown techniques. The insulation coatings were produced on Ag or AgMg sheathed Bi-2212 tapes and CuNb/sub 3/Sn wires by continuous, reel-to-reel sol-gel process. The coatings were then annealed at several temperatures and times. Dielectric constant and high voltage breakdown values for the insulation coatings were measured by using a capacitive technique and a high voltage breakdown-AC dielectric tester, respectively. The electrical properties of the coatings with dopant materials, number of dips, temperature and time of annealing process are presented.

Development of 100% lattice match buffer layers on RABiTS Ni tapes by sol-gel

Gd/sub 2/O/sub 3/-Yb/sub 2/O/sub 3/ and Gd/sub 2/O/sub 3/-Ho/sub 2/O/sub 3/ mixed RE oxides were used to produce buffer layers with a perfect lattice match with superconducting layer. Since these RE oxides are 100% miscible in each other, pseudocubic lattice parameter of the buffer layers can be modified by changing the ratio of components to perfectly match with any superconducting RE-123. Texture and the microstructure of the buffer layers were studied by XRD, Pole Figure and ESEM.

Textured buffer layers for YBCO coated conductors by continuous sol-gel processing

In order to develop alternative buffer layers for YBCO coated conductors, RE/sub 2/O/sub 3/ (RE=La, Pr, Sm, Eu, Gd, Tb, Ho, Yb, and Lu) thin films were studied as candidate materials. Buffer layers were grown on Ni tapes using organometallic compounds that are 2,4-pentanedionates, isopropoxides, and acetates by a continuous, non-vacuum sol-gel process. Films were annealed at 900/spl deg/C-1200/spl deg/C under 4%H/sub 2/-Ar gas mixture. The buffer layers were characterized by means of ESEM, SEM, EDS, XRD and pole figure analysis. Textured, pinhole free crack free, continuous buffer layers were obtained by using 2,4-pentanedionates.

Y-and Yb-123 coated conductor development by PLD and sol-gel on (Gd/sub 1-x/Er/sub x/)/sub 2/O/sub 3/ buffered Ni tapes

YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// and YbBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// layers were coated by sol-gel and PLD on Gd/sub 1.91/Er/sub 0.09/O/sub 3/ (100% lattice match with Y- and Yb-123) textured buffer layer on Ni substrates. Different thickness of buffer layers and superconducting layer were tried to see the thickness effect on superconducting properties. Buffer layers were prepared with different lattice parameters for Y-123 and Yb-123. Coated conductors were characterized by means of XRD, ESEM and T/sub c/ and J/sub c/ measurement. Since the perfect lattice match can be achieved between buffer layer and superconducting layer, texture of superconducting film was improved, and consequently critical current density of Y- and Yb-123 were improved.

Processing dependence of texture development in La2Zr2O7 buffer layer by sol-gel technique for YBCO coated conductors

Perovskite textured La2Zr2O7 (LZO) films were deposited on Ni tapes using sol-gel process for fabrication of second generation high-Tc superconductors. LZO solutions were derived from acetate and alkoxide precursors. The effects of precursors, solvents, chelating agents, and annealing conditions (temperature and time), on epitaxial growth of LZO were investigated by XRD, SEM, EDS, and X-ray pole figure analysis. It was found that texture of LZO depended on, solution preparation, and annealing conditions. Textured, homogenous, dense, crack free and pinhole free, LZO films were produced on textured Ni tapes by postannealing at 1150 °C for 10 min under 4%H2-Ar gas flow when lanthanum (III) 2-methoxyethoxide precursor and 2-methoxyethanol solvent were used. When lanthanum acetate precursor and trifluoroacetic acid were used, texture was obtained at 1160 °C for 40 min annealing conditions.

YBCO coated conductor development by continuous sol-gel process

YBCO coated conductor development on Ni tapes with various sol-gel buffer layers were investigated by a continuous, reel-to-reel sol-gel technique. YBCO films were prepared using solutions of various Y, Ba, and Cu precursor organometallic compounds. The coated YBCO tapes were annealed under argon/oxygen flow. ESEM, EDS, and XRD analysis were used to characterize the YBCO films. Sol-gel YBCO coated conductor on sol-gel buffered Ni tapes yielded a Tc,onset of 90 K and Jc of about 105 A/cm2. The films produced in this manner were homogeneous, and free of cracks.

High voltage breakdown capabilities of high temperature insulation coatings for HTS and LTS conductors

High temperature ZrO2 based coatings were deposited on Ag and Ag/AgMg sheathed Bi-2212 tapes from solutions derived from alkoxide-based precursors using a reel-to-reel, continuous sol-gel technique. The insulation coatings were annealed at 850 °C for 20 hours under O2 flow. The surface morphology and structure of coatings were characterized by SEM and XRD. High voltage breakdown of insulation on tapes was measured by a standard high voltage breakdown power supply. It has been found that high voltage breakdown values of these insulations strongly depend on number of dipping, thickness, coating type, annealing conditions, and dopant content in ZrO2. 20% Y2O3-ZrO2 coatings showed the best high voltage breakdown value, 2.05 kV at 1.5 mA.

Growth and Characterization of YbBCO Films on Textured Gd2O3 Buffer-Layered Ni Tapes: All Sol–Gel Process

YbBa2Cu3O7−x (YbBCO) thick films were grown on buffered, cube-textured Nickel tapes by sol–gel dip-coating method. Yb-123 films were prepared using solutions of Yb, Ba, and Cu organometallic compounds. A solution-based Gd2O3 buffer layer was deposited by dip-coating process with excellent texture and uniformity. The texture development and surface morphology of the buffer-layer films were examined by X-ray diffraction, pole figures, and ESEM analysis. Microstructure and characterization of Yb-123 films were done by ESEM, EDS, and XRD analysis. Tc and Jc were conducted by four-wire measurement method

The effects of NiO microstructure on the properties of sol-gel YBCO coated conductors

Bi-axially textured Ni tapes were oxidized to form NiO as alternative buffer layers for sol-gel YBCO coated conductors. We investigated growth and stability of YBCO films on nickel oxide buffer layers without using a cap layer. Microstructure of NiO, and effects of the microstructure on the properties of YBCO were also examined. To understand microstructure formation of NiO layers, parameters of surface oxidation process such as oxidation time, temperature and atmosphere were studied. Surface morphology, thickness of NiO and YBCO layers, were studied using environmental scanning electron microscopy (ESEM). We found that surface oxidation parameters strongly affect microstructure, thickness, and morphology of NiO, and the properties of YBCO. Resistance versus temperature measurements of YBCO coated conductors was done by 4-probe measurements.