Rama Nekkanti

Pulsed laser deposition of YBCO coated conductor using Y2O3 as the seed and cap layer

Although a variety of buffer layers have been routinely reported, a standard architecture commonly used for the Y Ba2Cu3O7−x (YBCO) coated conductor is Y BCO/CeO2/Y SZ/CeO2/substrate or Y BCO/CeO2/Y SZ/Y2O3/substrate where ceria is typically the cap layer. CeO2 is generally used as only a seed (or cap layer) since cracking within the film occurs in thicker CeO2 layers due to the stress of lattice mismatching. Y2O3 has been proposed as a seed and as a cap layer but usually not for both in a given architecture, especially with all layers deposited in situ. Yttrium oxide films grown on nickel by electron beam evaporation processes were found to be dense and crack free with good epitaxy. In this report, pulsed laser deposition (PLD) of Y2O3 is given where Y2O3 serves as both the seed and cap layer in the YBCO architecture. A comparison to PLD CeO2 is provided. Deposited layers of the YBCO coated conductor are also grown by laser ablation. Initial deposition resulted in specimens on textured Ni substrates with current densities of more than 1 MA cm−2 at 77 K, self-field.

Copper Metallic Substrates for High Temperature Superconducting Coated Conductors

Biaxially cube textured polycrystalline Cu(200) substrate tapes were produced for high temperature superconducting (HTS) coated conductor applications. A comparison is made between Cu substrates fabricated by reverse cold rolling followed by recrystallization, from stock materials that were obtained in the form of extruded rod and rolled plate. Detailed x-ray diffraction (XRD) studies and orientation imaging microscopy (OIM) were performed to measure the in-plane alignment, out-of-plane alignment, and microtexture at various deformation levels and annealing temperatures. The rod starting geometry proved to have superior biaxial alignment with a predominant (220) deformation texture after rolling. Phi (Φ) scan and psi (Ψ) scan XRD reveals that the best in-plane and out-of-plane alignment, measured in terms of full width half maximum (FWHM) values of 5.4° and 5.8°, were obtained at 99.5% reduction in thickness and 750 °C annealing temperature. OIM microtexture results indicate that more than 97.5% of grains had less than 10° misorientation with no observable twinning.

Development of nickel alloy substrates for Y-Ba-Cu-O coated conductor applications

Fabrication of long-length, textured substrates constitute a critical step in the successful application of coated High Temperature Superconductors (HTS). Substrate materials stronger than nickel are needed for robust applications, while substrates with non-magnetic characteristics are preferred for AC applications. The present work is thus focused on development of texture in high strength, non-magnetic substrate materials. As the development of cube texture is easier in medium to high stacking fault energy materials, binary alloys based on nickel were evaluated for the present application. High purity alloys were melted and hot/cold worked to obtain thin tapes. The development of texture in these alloys as a function of processing parameters was studied by X-ray diffraction and metallographic techniques. Orientation Imaging Microscopy (OIM) was used to quantify the extent of texture development in these substrates. Results to date on the development of texture by thermo-mechanical processing of these alloys are presented.

YBa2Cu3O7−x–Ag thick films deposited by pulsed laser ablation

Abstract Ag-doped YBa 2 Cu 3 O 7− x films, with thickness ranging from 0.06 to 2.5 μ m, were deposited by pulsed laser ablation onto (100) LaAlO 3 single-crystal substrates. The target was YBa 2 Cu 3 O 7− x with 5 wt.% Ag addition. The presence of Ag in the films in concentrations of ∼1 at.% was detected by X-ray fluorescence and secondary ion mass spectrometry (SIMS) analysis. Biaxial alignment of the films was indicated by φ scans with full-width-half-maximum (FWHM) spread of 1–2° for various thicknesses. Utilizing a standard deposition process, most films showed a critical transition temperature ( T c ) >90 K as measured by the ac susceptibility technique. Film critical current densities ( J c ) on the order of 10 6 A/cm 2 were measured at 77 K with a four-probe technique on a 100- μ m-wide patterned microbridge.

XPS depth profiling studies of YBCO layer on buffered substrates

XPS studies of a typical YBCO coated conductor architecture were conducted to investigate the chemical and microstructural profiles. The detailed XPS depth profiling study was performed on one sample (YBCO/CeO2/YSZ/CeO2/Ni) of coated conductor. The chemical depth profiling involved bombarding a small area of the specimen surface with 3 keV Ar+ ions and analyzing the freshly exposed surface after each bombardment. Results of the process show that the Y(3d) photo-electronic peak shape in these films is very different from bulk (sintered and oxygen annealed) YBCO superconductors and surface analysis of YBCO thin films. This may indicate a possible difference in the atomic co-ordination between some laser-ablated films and bulk sintered ones. The correlation between chemical binding states of the ions and superconducting properties need to be investigated in details. The lower portion of the YBCO film showed distinct signs of contamination including Ce, and traces of Ni. An initial report of Zr diffusion into...

Laser surface texturing of metallic substrates

A low power AO Q-switched Nd:YAG laser operating at 1064 nm has been used to texture the surface of metallic substrates such as nickel, hastelloy, and aluminum. The substrate surface is uniformly exposed to the laser by using a scan head to raster the focused beam across the substrate surface in a specific pattern. The surface texturing effect is manipulated by appropriate choice of laser power, frequency, scan speed, and focal spot size. Texturing the surface in this manner removes contaminants such as debris, oils, and small scratches and also re-flows the surface layer of the metal. The laser parameters, along with surface melt depth and surface morphology, are being used to provide data for modeling the laser interaction with the metal surface. The discussion of the experimental results and initial modeling calculations will be presented.A low power AO Q-switched Nd:YAG laser operating at 1064 nm has been used to texture the surface of metallic substrates such as nickel, hastelloy, and aluminum. The substrate surface is uniformly exposed to the laser by using a scan head to raster the focused beam across the substrate surface in a specific pattern. The surface texturing effect is manipulated by appropriate choice of laser power, frequency, scan speed, and focal spot size. Texturing the surface in this manner removes contaminants such as debris, oils, and small scratches and also re-flows the surface layer of the metal. The laser parameters, along with surface melt depth and surface morphology, are being used to provide data for modeling the laser interaction with the metal surface. The discussion of the experimental results and initial modeling calculations will be presented.