Suresh Annavarapu

Low-cost YBCO coated conductor technology

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 0.8 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.

YBCO coated conductors by an MOD/RABiTS/spl trade/ process

Commercialization of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) superconducting coated conductor composite (CCC) technology requires a cost-effective continuous manufacturing process. High critical current YBCO CCC wires with excellent uniformity over length have been fabricated using an all-continuous process. The conductor architecture consists of a metal organic derived YBCO layer, coated on a deformation-textured NiW alloy substrate buffered with Y/sub 2/O/sub 3//YSZ/CeO/sub 2/. Critical current at 77 K, self-field, of up to 118 A was achieved in 1 cm-wide tapes over 1.25 meter lengths, with a standard deviation of 3% measured on a 5 cm scale. The high uniformity and performance supports the feasibility of commercial long-length CCC wire based on deformation textured metal substrates and solution-based deposition of YBCO.

Low cost Y-Ba-Cu-O coated conductors

Solution-based techniques have been examined as potential low-cost processes for manufacturing YBCO coated conductors. YBCO films prepared from metal trifluoroacetate precursors have achieved performance levels equaling or exceeding that of vapor deposited films with the same thickness on CeO/sub 2//YSZ(sc) substrates. J/sub c/s of 4.5 MA/cm/sup 2/ and 2 MA/cm/sup 2/ have been achieved in 0.4 /spl mu/m thick YBCO films on CeO/sub 2//YSZ(sc) and CeO/sub 2//YSZ/CeO/sub 2//Ni substrates, respectively. Textured Gd/sub 2/O/sub 3/ buffer layers have been deposited on deformation textured Ni substrates in a reel-to-reel process. The performance of YBCO films deposited on substrates containing the Gd/sub 2/O/sub 3/ seed layers is comparable in performance to YBCO films grown on all vacuum deposited buffer layers.

YBCO coated conductors by an MOD/RABiTS™ process

Commercialization of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) superconducting coated conductor composite (CCC) technology requires a cost-effective continuous manufacturing process. High critical current YBCO CCC wires with excellent uniformity over length have been fabricated using an all-continuous process. The conductor architecture consists of a metal organic derived YBCO layer, coated on a deformation-textured NiW alloy substrate buffered with Y/sub 2/O/sub 3//YSZ/CeO/sub 2/. Critical current at 77 K, self-field, of up to 118 A was achieved in 1 cm-wide tapes over 1.25 meter lengths, with a standard deviation of 3% measured on a 5 cm scale. The high uniformity and performance supports the feasibility of commercial long-length CCC wire based on deformation textured metal substrates and solution-based deposition of YBCO.

Growth and characterization of oxide buffer layers for YBCO coated conductors

Metal oxide films were grown on single crystal oxide substrates and deformation textured metal substrates by a metal organic deposition technique using metal alkoxides as the starting precursor materials. The crystallinity, grain alignment, and morphology of the oxide films depend on the process conditions and the substrate properties. Epitaxial oxide films were grown under a range of oxygen partial pressures and temperatures required for film formation on technologically important metal substrates. YBCO films grown on epitaxial LaAlO/sub 3/ buffer layers on single crystal SrTiO/sub 3/ had J/sub c/s of 2.2 MA/cm/sup 2/ (77 K, self-field) demonstrating the quality of the MOD derived oxide films.

Non-magnetic substrates for low cost YBCO coated conductors

CuNiAl and NiCr alloys were made and processed to non-magnetic, bi-axially textured substrates. Epitaxial YSZ and YBCO were deposited by pulsed laser deposition on the CuNiAl. Samples were cross sectioned and investigated with TEM. It appears that Al forms a thin oxide layer at the CuNiAl surface that acts as a template for the subsequent YSZ layer. The 1.2 /spl mu/m YBCO layer had a current density of 0.16 MA/cm/sup 2/ at 75 K and self field. On the NiCr substrates an Y/sub 2/O/sub 3/ seed layer was deposited with E-beam evaporation, followed by RF sputter deposition of YSZ and a CeO/sub 2/ cap layer. These substrates were coated with a 0.4 /spl mu/m YBCO layer using a trifluoroacetate solution, a very cost effective metal-organic deposition process. These samples carried critical currents exceeding 0.7 MA/cm/sup 2/ at 77 K, self field.

Progress towards a low-cost coated conductor technology

Abstract Progress in the development of an economically and technically viable YBCO coated conductor technology for HTS wire using deformation-textured buffered substrates and solution-deposited superconductor layers is reported. Biaxially textured Ni substrates have been fabricated using a deformation texturing process. Epitaxial oxide buffer layers have been deposited by a combination of e-beam deposition and magnetron sputtering. Epitaxial YBCO films have been grown using a trifluoroacetate solution precursor. The resulting composite conductors have critical current densities approaching 2 MA/cm 2 at 77K in self-field. Critical current densities of 4.5 MA/cm 2 have been also obtained on CeO 2 buffered YSZ single crystal substrates, demonstrating performance parity with vacuum deposited YBCO films.

Progress towards a low-cost commercial coated conductor

YBCO films prepared from metal trifluoroacetate (TFA) precursors on oxide-buffered textured non-magnetic substrates have achieved performance levels equaling that on oxide buffered textured Ni substrates. Critical current densities of 0.7 MA/cm 2 to 1.0 MA/cm 2 have been achieved in 0.4 µm thick YBCO films on short-length of CeO 2 /YSZ/Y 2 O 3 /Ni/Ni-13wt%Cr substrates. High-quality epitaxial buffers comprising a Ni layer, Y 2 O 3 seed, YSZ barrier and CeO 2 cap layers have been deposited over meter long tapes of deformation textured Ni and Ni-13%Cr using reel-to-reel processes. High-performance TFA-based YBCO films have been deposited on 0.1 m to 0.3 m lengths of these oxide buffered substrates using reel to reel processes. Critical current densities up to 1.0 MA/cm 2 have been achieved in 0.4 µm thick YBCO films on CeO 2 /YSZ/Y 2 O 3 /Ni substrates. Using multiple coats of the metal trifluoroacetate precursors, thicker YBCO films have been demonstrated on oxide buffered substrates. Critical currents in excess of 100A/cm-width have been achieved for 1.2 µm -1.6 µm thick YBCO films on short lengths of CeO 2 /YSZ/Y 2 O 3 /Ni substrates.