Process for the production of a crystal-oriented surface layer of a ceramic high temperature superconductor
AssigneeAsea Brown Boveri AG
InventorsFelix Greuter, Claus Schuler
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Abstract
Process for the production of a polycrystalline, crystal-oriented layer of a high temperature superconductor of the class (Y,RE) Ba.sub.2 Cu.sub.3 O.sub..apprxeq.7 on a substrate or between two substrates of Ag or an Ag alloy containing up to 20% by weight Au, Pd or Pt, wherein a first powder layer, of at most 5 .mu.m thickness and consisting of the simple oxides and/or mixed oxides of the elements Y, Ba, Cu in the ratio Y:Ba:Cu:O=1:2:3:6.5, is first applied, and on it is applied a second powder layer of the superconducting substance (Y,RE) Ba.sub.2 Cu.sub.3 O.sub..apprxeq.7 in a thickness of 5-10 .mu.m, and the whole is sintered in an O.sub.2 -containing atmosphere.
Claims13
A process for the production of a polycrystalline crystal-oriented layer of a ceramic high temperature superconductor, having the nominal composition YBa.sub.2 Cu.sub.3 O.sub.6.5+y where 0<y<1, wherein said superconductor is applied to a substrate in the form of a powder layer and is then sintered at a sintering temperature, said process further comprising the steps of:
- providing said substrate consisting of pure metallic silver or a silver alloy containing up to 20% by weight of Au, Pd or Pt;
- applying onto said substrate a first layer of a first powder having a particle diameter or less than 2 microns, said first powder consisting of simple oxides and/or mixed oxides of the elements Y, Ba, Cu or the oxides of the elements Y and Cu and the carbonate of Ba, corresponding to the stoichiometric ratio Y:Ba:Cu:O=1:2:3:6.5, said first layer having a thickness of at most 5 microns, which first powder creates a melt at said sintering temperature and transforms into said superconductor during said sintering step;
- applying onto said first layer a second layer having a thickness of 5-10 microns of a second powder, said second powder containing 1-10 mol % of said first powder, the remainder being said superconducting powder;
- and
- sintering said substrate with said first and second layers in an atmosphere containing at least 20% by volume O.sub.2, the remainder being N.sub.2 or an inert gas, under a total gas pressure of at least 1 bar and a sintering temperature of at least 885.degree. C. and at most 927.degree. C., wherein said sintering step comprises
- first heating at a rate of at most 50.degree. C./h to 400.degree. C.;
- heating at a rate of at most 300.degree. C./h to said sintering temperature;
- holding at said sintering temperature for 30 minutes, whereupon a liquid phase of 0.1-5% by volume is transitorily formed in said first layer;
- cooling at a rate of at most 100.degree. C./h to 600.degree.-400.degree. C., and holding at this temperature for 2 hours;
- and
- cooling at a rate of at most 100.degree. C./h to room temperature.
Dependencies are inferred from the claim text.