Novel Preparation Methods for High TcOxide Superconductors

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Abstract
High Tc oxide superconductors can be prepared by a variety of novel metallurgical or ceramic processing techniques. For example, forming metallic precursors of YBa2Cu3 or REBa2Cu3, where RE is a rare earth element, followed by oxidation has yielded the corresponding ceramic oxide in pellet, wire, and thin film forms. Ceramic fabrication techniques (which often involve incorporating fine particles of the ceramic in a suitable vehicle) such as doctor-blade tape casting and screen printing have been utilized to synthesize both tapes and thin films. Due to intense worldwide effort to develop these ceramics into useable forms, many unique fabrication techniques have been employed, such as the melt-textured growth method of Jin et al. and dynamic compaction. In addition, it is likely that numerous laboratories, particularly industrial, are developing proprietary methods to fabricate wire and other forms but have not published these results due to the intensely competitive nature of this area. In this article, we review some of the methods reported so far for preparing high Tc ceramic superconductors, and we discuss one example of a proprietary method being developed at one of the author's (LDW) laboratories.Tapes of YBa2cu3O7-x fabricated using the doctor-blade tape casting technique were first displayed by AT&T Bell Laboratories scientists at the 1987 March meeting of the American Physical Society. This method involves mixing ceramic powder, a binder to provide green (unfired ceramic) strength, a plasticizer to provide flexibility, a dispersant to prevent particle agglomeration and a solvent. After mixing all these components together, the solution is poured into a “doctor blade” device which allows a controlled thickness of material to be deposited on a plastic film carrier that passes underneath the doctor blade.