Deformation-textured, non-silver substrates, and solution-based deposition of buffer and superconductor layers offer routes to a low-cost YBCO coated-conductor technology for high-temperature superconducting wire Several significant steps towards such a technology are reported here: a solution-based Gd2O3 seed buffer layer was deposited by a web-coating technique over a metre-length tape of deformation-textured nickel with excellent texture and uniformity Also, short full-stack samples with YBCO performance up to 08 MA cm-2 at 77 K were prepared at Oak Ridge National Laboratory (ORNL) and American Superconductor (ASC) using a CeO2/YSZ/CeO2 buffer sequence on textured nickel and a trifluoroacetate (TFA) precursor YBCO process; in this case the buffers are deposited by e-beam and magnetron sputtering

https://iopscience.iop.org/article/10.1088/0953-2048/13/5/308/pdf

Low-cost YBCO coated conductor technology

The biaxial textures created in metals by rolling and annealing make them useful substrates for the growth of long lengths of biaxially textured material. The growth of overlayers such as high-temperature superconductors requires flat substrates with a single, sharp texture. A sharp cube texture is produced in high-purity Ni by rolling and annealing. We report the effect of rolling reduction and annealing conditions on the sharpness of the cube texture, the incidence of other orientations, the grain size and the surface topography. A combination of high reduction and high-temperature annealing in a reducing atmosphere leads to >99% cube texture, with a mosaic of about the rolling direction, about the transverse direction, and about the normal direction.

/pdf/cube-textured-nickel-substrates-for-high-temperature-39hv5q6i1a.pdf

Cube-textured nickel substrates for high-temperature superconductors

A solution process was used to grow epitaxial La 2 Zr 2 O 7 (LZO) buffer layers on roll-textured Ni (100) substrates to produce YBa 2 Cu 3 O 7− δ (YBCO)-coated conductors. The LZO precursor solution was prepared by an all alkoxide sol–gel route using mixed metal methoxyethoxides in 2-methoxyethanol. The partially hydrolyzed solution was either spin-coated or dip-coated onto the textured Ni substrates. The amorphous thin film was then heat treated at 1150°C under (96%)Ar/(4%)H 2 atmosphere for 1 h. X-ray diffraction (XRD) of the buffer layer indicated a strong c -axis orientation on the Ni (100) substrate. The LZO (222) pole figure revealed a single cube-on-cube texture. SEM images of the LZO buffer layer showed a dense microstructure without cracks. The YBCO deposited on the sol–gel LZO-buffered Ni substrates with sputtered YSZ and CeO 2 top layers had a critical current density of 480,000 A/cm 2 at 77 K and self-field.

Epitaxial growth of La2Zr2O7 thin films on rolled Ni-substrates by sol-gel process for high Tc superconducting tapes

Short segments of YBa2Cu3O7-y (YBCO) coated conductors were fabricated on rolling-assisted biaxially textured substrates (RABiTS) with a layer sequence of CeO2/YSZ/Ni using an ex situ BaF2 precursor process. Pulsed laser deposition (PLD) was used to deposit both YSZ and CeO2 layers. The YBCO films were grown using e-beam coevaporated Y–BaF2–Cu precursors followed by postannealing. An overall engineering current density, JE, of 28,000 A/cm2 and critical current, Ic, of 147 A/cm width at 77 K were achieved for a 1.6-μm-thick YBCO film. This result demonstrates the possibility of using both the ex situ BaF2 precursor approach and the RABiTS process for producing long lengths of high-JE coated conductors.

YBa2Cu3O7-y−coated conductors with high engineering current density

Thin films of the Tl-based high-temperature superconducting (HTS) phases are beginning to find application in a number of practical devices, especially in the field of microwave communication systems. This review describes the issues surrounding the fabrication of thin films of the thallium-based HTS materials. The influence of thermodynamics and kinetics, the various potential thalliation techniques and the selection of an appropriate substrate material are all important considerations when designing a process for the fabrication of thin films of these highly reactive materials. The properties of the resulting films are critically dependent on the microstructures developed during thalliation. Microstructural evolution during thalliation, the effect of structural defects on the properties of such films and the importance of achieving biaxial grain alignment in optimizing the properties of the films are all discussed.

Thallium-based HTS thin films, processing, properties and applications

Epitaxial film growth of Tl0.78Bi0.22Sr1.6Ba0.4Ca2Cu3O9 ((Tl,Bi)-1223) on rolling assisted biaxially textured substrates with YSZ and CeO2 buffer layers (RABiTS) has been successfully demonstrated by laser ablation and post-deposition annealing in flowing argon. X-ray diffraction (XRD) θ-2θ spectra showed that the films consisted mainly of c-axis aligned 1223 phase with some intergrown 1212 phase, while XRD Φ-scans of (102) pole figure revealed that the films are also a- and b-axes aligned, with an epitaxy of the «100» of (Tl,Bi)-1223 film on the «110» of the top YSZ buffer layer. Four-terminal electrical transport measurements showed that the zero-resistance transition temperature (Tc) was in the range of 106 - 110 K, and the critical current density (Jc) at 77 K and zero field was about 105 A/cm2 for the entire film width (3 mm) of a longer film (14 mm) which was processed differently from the shorter films (7 mm). For a shorter film (7 mm) that showed better ab-in-plane alignment, the magnetization Jc, at 77 K and extrapolated to zero field, calculated from Bean's model using the full film width (3.5 mm) as the appropriate lateral dimension, was 2 × 105 A/cm2.

Epitaxial Film Growth of Tl0.78Bi0.22Sr1.6Ba0.4Ca2Cu3O9 on Rolling Assisted Biaxially Textured Nickel Substrates with YSZ And CeO2 Buffer Layers

High current YBa/sub 2/Cu/sub 3/O/sub 7-y/ (YBCO) and Tl/sub 0.78/Bi/sub 0.22/Sr/sub 1.6/Ba/sub 0.4/Ca/sub 2/Cu/sub 3/O/sub 9-y/ (Tl,Bi-1223) coated conductors were fabricated on Rolling-Assisted Biaxially Textured Substrates (RABiTS) with a layer sequence of CeO/sub 2//YSZ/CeO/sub 2//Ni. The top and bottom CeO/sub 2/ (Cerium oxide) layers were deposited epitaxially on textured-Ni [100] substrates using reactive evaporation of Ce metal. The thickness of the CeO/sub 2/ films was 200-400 /spl Aring/. The YSZ (Yttria Stabilized Zirconia) layers were also deposited epitaxially on CeO/sub 2/-buffered Ni substrates either by rf magnetron sputtering or e-beam evaporation. The thickness of the YSZ films was typically 3000-9000 /spl Aring/. The e-beam CeO/sub 2/ films were dense, crack-free and columnar. The microstructure of sputtered YSZ was dense and the e-beam deposited YSZ was porous. To understand the stability of these buffer layers, the as-grown CeO/sub 2/-buffered YSZ (both sputtered and e-beam)/CeO/sub 2//Ni substrates were annealed in a controlled oxygen furnace at various temperatures. RBS studies indicate that the YSZ sputtered films were quite stable up to 780/spl deg/C and 200-mTorr oxygen. For e-beam YSZ films, there was an indication of diffusion of oxygen through these buffers into the Ni substrate. The Tl,Bi-1223 films were grown on all e-beam buffers using pulsed laser ablation of precursor films followed by post-annealing. The YBCO films were grown on e-beam/sputtered buffers using e-beam co-evaporated Y-BaF/sub 2/-Cu precursors followed by post-annealing.

Optimization of buffer layers on rolled-Ni substrates for high current YBCO and Tl,Bi-1223 coated conductors using ex-situ precursor approaches

Abstract In-plane aligned superconducting Tl 0.78 Bi 0.22 Sr 1.6 Ba 0.4 Ca 2 Cu 3 O 9 ((Tl,Bi)-1223) films on R olling A ssisted Bi axially T extured S ubstrates (RABiTS) with J c of 4.25×10 5 A/cm 2 at 77 K and zero-field have been synthesized by laser ablation and post-ablation annealing. The as-ablated films were amorphous due to the low substrate temperature during ablation. The amorphous films were then wrapped together with an unfired Tl 0.95 Bi 0.22 Sr 1.6 Ba 0.4 Ca 2 Cu 3 O 9 pellet in silver foil. The whole package was finally annealed in a tube furnace at 780–810°C for 40–60 min in flowing argon to crystallize the films. X-ray diffraction (XRD) shows that the annealed films consist of mainly c -axis aligned (Tl,Bi)-1223 phase with a small amount of (Tl,Bi)-1212 phase. The full width at half maximum (FWHM) values of XRD peaks show that both phases are epitaxial, with in-plane and out-of-plane alignments comparable to those of the underlying Ni and buffer layers (CeO 2 and YSZ). Four-probe transport measurements showed superconducting transition temperatures ( T c s) of 105–109 K depending on the annealing conditions. With external magnetic field applied parallel to the c -axis, irreversibility magnetic fields reached beyond 3 T at 77 K and beyond 5 T at 64 K.

J.Y. Lao

Papers

Epitaxial Film Growth of Tl0.78Bi0.22Sr1.6Ba0.4Ca2Cu3O9 on Rolling Assisted Biaxially Textured Nickel Substrates with YSZ And CeO2 Buffer Layers

Optimization of buffer layers on rolled-Ni substrates for high current YBCO and Tl,Bi-1223 coated conductors using ex-situ precursor approaches

In-plane aligned superconducting Tl0.78 Bi0.22 Sr1.6 Ba0.4 Ca2 Cu3 O9 films on rolling assisted biaxially textured substrates

Ex-Situ Processing of Ti-Containing Films