Reactions at Ceramic Superconductor/Metal Interfaces
- PDF / 1,554,354 Bytes
- 4 Pages / 420.48 x 639 pts Page_size
- 13 Downloads / 194 Views
REACTIONS AT CERAMIC SUPERCONDUCTOR/METAL INTERFACES
Min-Seok Oh and Michael R. Nods Lehigh University Department of Materials Science and Engineering Bethlehem, PA 18015 ABSTRACT Joining technology for ceramic superconductors is currently a major problem. The possible reactions which occur at ceramic superconductors/metal interfaces are discussed and examples are shown of interfaces between YBa 2Cu3O and Ndt.85 Ceo.15 CuO 4 -x vs. a series of metals (Ag, Ni, Fe) now being considered for joining and cladding applications. Various characterization techniques, including EPMA and x-ray mapping, are utilized for analyzing the spatial distribution of reaction products. In a composite configuration, Ag interlayer is found to promote interfacial reactions. INTRODUCTION Since high T, ceramic superconductors were discovered a few years ago, many attempts have been made to develope them for practical applications. Materials synthesis for the high current density capacity, fabricability of thin film and wire, and protection from various environments are basic issues for increasing their commercial value. In any useful configuration, superconductors must make contact with other materials. It has already been reported that the properties of the superconducting YBa 2Cu 3O phase are degraded by exposure to range of environments, including H20 and CO2 . Therefore, contact with either a gas phase or other solid phase materials can promote interfacial reactions, and change oxygen stoichiometry as a function of depth which eventually affects the superconductivity, or nonsuperconducting layers may form. Noble metals, such as Au or Ag, show the least tendency to produce reaction layer in contact with the superconductor, when they are used as electrical contacts or encapsulants. In our experiments, interfacial reactions occurred after the heat treatment of YBa 2Cu 3 OJ/Ag/403SS (stainless steel) in an Ag tube clad with other metals during wire processing. Because the presence of copper ions in superconducting phase is a major reason for the reactivity of the superconducting ceramics, we report here work on CuO/Ag/Ni specimens with similar configuration. Finally, Nd1 .g5Ceol5CuO4-x, which was recently discovered to be a n-type superconductor[l ], and which may show less reactivity in some circumstances because of its lower Cu valence state, has also been fabricated in a similar composite configuration. EXPERIMENTS YBa 2 Cu3O superconducting powder was prepared by first ball milling in absolute alcohol and then calcining the mixed components in air at 850 OC. Sintering was performed in air at 920 oC for 4 hours, and this material was then given a oxygen anneal at 500 OC for 10 hours and then fumace-cooled. After sintering, the powder was grounded in a mortar and pestle. Nd1.s 5 Ceo05 CuO4-x powder was also obtained by solid state reaction of Nd 20 3, CeO 2 , and CuO[2]. In both cases, the powder was packed into an Ag tube (6.35mm OD., 5.84mm ID.), which was placed inside a thick wall tube of either 403 stainless steel or nickel. Drawing
Data Loading...
