Evaluation of methods for application of epitaxial buffer and superconductor211 layers

摘要

The recent achievements of critical currents exceeding million amperes per square211u001ecentimeter at 77K in YBCO deposited over suitably textured substrate have 211u001estimulated interest in the potential applications of coated conductors at high 211u001etemperatures and in high magnetic fields. Currently, ion-beam assisted deposition 211u001e(IBAD), and rolling assisted bi-axially textured substrate (RABiTS), represent 211u001etwo available options for obtaining textured substrates. For applying suitable 211u001ecoatings of buffer and high temperature superconductor (HTS) material over 211u001etextured substrates, several options are available which include sputtering, 211u001eelectron-beam evaporation, laser ablation, electrophoresis, chemical vapor 211u001edeposition (including metal organics chemical vapor deposition), sol-gel, metal 211u001eorganics decomposition, electrodeposition and aerosol/spray pyrolysis. A 211u001ecommercial continuous long-length wire/tape manufacturing scheme developed out of 211u001eany suitable combination of the above techniques would consist of operations 211u001einvolving preparation of the substrate and application of buffer, HTS and 211u001epassivation/insulation materials and special treatment steps such as post-211u001eannealing. These operations can be effected by various process parameters that 211u001ecan be classified into chemistry, materials, engineering and environmental 211u001erelated parameters. Under the DOE-sponsored program, to carry out an engineering 211u001eevaluation, first, the process flow schemes were developed for various candidate 211u001eoptions identifying the major operating steps, process conditions, and process 211u001estreams. Next, to evaluate quantifiable parameters such as process severity (e.g. 211u001etemperature and pressure), coating thickness and deposition rate for HTS 211u001ematerial, achieved maximum J(sub c) value (for 1(micro)m thick) and cost of 211u001echemical and material utilization efficiency, the multi-attribute method was used 211u001eto determine attributes/merits for various parameters and candidate options. To 211u001edetermine similar attribute values for the non-quantifiable parameters, a 211u001esubjective evaluation was used. Results of the two evaluations were then combined 211u001eto calculate the overall merit/utility of a given option using weighting factors. 211u001eTo evaluate the effect of arbitrarily determined weighting factors, a sensitivity 211u001eanalysis was carried out by using three different sets of weighting factors. In 211u001ethe end, the results of the overall utility/merit values calculated using 211u001edifferent sets of weighting factors were utilized to determine the preliminary 211u001eranking among the candidate options. As a result of this study, MOD, Sol-Gel, 211u001eMOCVD, E-Beam and PLD options have been identified as the leading candidates for 211u001econtinuous, long-length processing of coated HTS conductors. However, there are 211u001eseveral technical concerns related to each of these which need to be addressed 211u001efirst before a commercially viable option can be developed out of any one of 211u001ethem.