The RABiTS Approach: Using Rolling-Assisted Biaxially Textured Substrates for High-Performance YBCO Superconductors
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The RABiTS
Approach: Using Rolling-Assisted Biaxially Textured Substrates for High-Performance YBCO Superconductors
Amit Goyal, M. Parans Paranthaman, and U. Schoop Abstract This article provides an overview of the fabrication of epitaxial, biaxially aligned buffer layers on rolling-assisted biaxially textured substrates (RABiTS) as templates for YBCO films carrying high critical current densities. The RABiTS technique uses standard thermomechanical processing to obtain long lengths of flexible, biaxially oriented substrates with smooth surfaces.The strong biaxial texture of the metal is conferred to the superconductor by the deposition of intermediate metal and/or oxide layers that serve both as a chemical and a structural buffer. Epitaxial YBCO films with critical current densities exceeding 3 106 A/cm2 at 77 K in self-field have been grown on RABiTS using a variety of techniques and demonstrate magnetic-field-dependent critical current values that are similar to those of epitaxial films on single-crystal ceramic substrates. The RABiTS architecture most commonly used consists of a CeO2 (sputtered)/YSZ (sputtered)/Y2O3 (e-beam)/Ni-W alloy. The desired texture of the base metal has been achieved in 100 m lengths and 10 cm widths. Scaleable and cost-effective techniques are also being pursued to deposit the epitaxial multilayers. The results discussed here demonstrate that this technique is a viable route for the fabrication of long lengths of high-critical-current-density wire capable of carrying high currents in magnetic fields and at temperatures accessible by cooling with relatively inexpensive liquid nitrogen (up through the 77 K range). Keywords: coated conductors, high-temperature superconductors, RABiTS, rolling-assisted biaxially textured substrates, YBCO.
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Introduction First-generation superconductive wire that is currently commercially available is based on an inherently expensive technology using (Bi,Pb)2Sr2Ca2Cu3O10 (BSCCO) superconductive filaments in a silver matrix. This article describes second-generation (2G) YBa2Cu3O7– (YBCO)-coated conductors based on rolling-assisted biaxially textured substrates (RABiTS). In order to achieve full current-carrying capacity in a high-temperature superconductor (HTS) layer, a biaxially oriented template is required on which the YBCO layer can be deposited in near-single-crystal orientation. The RABiTS process involves thermomechanical biaxial texturing of a metal or alloy followed by epitaxial deposition of the buffer layers and the superconductor. In order to match lattice parameters and minimize any chemical interaction between the metal substrate and the oxide superconductor, epitaxial buffer layers are necessary. Buffer layers are used to provide a good diffusion barrier to oxygen from the superconductor and to cations from the substrate. A key challenge is to control epitaxial deposition of oxide thin films onto the superconductor in a continuous web-coating process, and to provide a good lattice match to the superconductor. Understanding buffer m
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