Bulk high temperature superconductors

High temperature superconductors are expected to form a substantial segment of the high-tech market of the 21st century, particularly in the areas of energy technology and medical diagnosis. In order to achieve this goal, extremely high supercurrents need to be established in the material, both at high magnetic fields and at "high" temperatures, i.e. at or near the boiling temperature of liquid nitrogen (77 K, - 196 C). From all known ceramic high temperature superconducting materials, the compound Y-Ba-Cu-O seems to be the most promising, but will have to be engineered with regard to its crystalline defect structure by nanotechnological techniques, in order to improve "flux pinning" that forms the basis for loss-free supercurrent flow in the presence of magnetic fields. Depending on the application under consideration, the material will have to be processed in one of two forms, either as a "coated conductor" or as a bulk pellet with large diameters. The first represents state-of-the-art solutions for the processing of "wires" or "tapes" in long lengths for all applications requiring the fabrication of coils or cables. This sector is not addressed in the present proposal. The second represents a completely new option for producing "permanent magnets" with unmatched field strength (presently up to about 15 T, depending on temperature), which can be used for levitation, as bearings, for motor components, etc., and of course as magnets. The present proposal addresses fundamental issues of flux pinning and supercurrent flow in these bulk pellets. The substantial progress made in processing over the past decade has enabled us to produce "single grain" pellets (without any large angle grain boundaries) with diameters of up to 10 cm. We intend to optimize the defect structure for flux pinning by innovative technologies providing defects on the nanometer scale, e.g. by very specific chemical doping, by the addition of special pre-fabricated nanometer sized normal conducting particles, or by radiation techniques. One particular strong point of the project is certainly the availability of new, highly localized characterization techniques that have been introduced by the Atomic Institute recently and which allow us to assess not only the global average of all supercurrents over the entire bulk pellet, but rather to monitor the local supercurrent flow on a sub-mm length scale, thus immediately indicating areas of weaker or stronger flux pinning. This information, together with standard structural characterizations of the pellets, is expected to lead to radical improvements in the material performance through immediate feedback with regard to the choice of the nano-scale defects and to the processing conditions.

High temperature superconductors are expected to form a substantial segment of the high-tech market of the 21st century, particularly in the areas of energy technology and medical diagnosis. In order to achieve this goal, extremely high supercurrents need to be established in the material, both at high magnetic fields and at "high" temperatures, i.e. at or near the boiling temperature of liquid nitrogen (77 K, - 196 C). From all known ceramic high temperature superconducting materials, the compound Y-Ba-Cu-O seems to be the most promising, but will have to be engineered with regard to its crystalline defect structure by nanotechnological techniques, in order to improve "flux pinning" that forms the basis for loss-free supercurrent flow in the presence of magnetic fields. Depending on the application under consideration, the material will have to be processed in one of two forms, either as a "coated conductor" or as a bulk pellet with large diameters. The first represents state-of-the-art solutions for the processing of "wires" or "tapes" in long lengths for all applications requiring the fabrication of coils or cables. This sector is not addressed in the present proposal. The second represents a completely new option for producing "permanent magnets" with unmatched field strength (presently up to about 15 T, depending on temperature), which can be used for levitation, as bearings, for motor components, etc., and of course as magnets. The present proposal addresses fundamental issues of flux pinning and supercurrent flow in these bulk pellets. The substantial progress made in processing over the past decade has enabled us to produce "single grain" pellets (without any large angle grain boundaries) with diameters of up to 10 cm. We intend to optimize the defect structure for flux pinning by innovative technologies providing defects on the nanometer scale, e.g. by very specific chemical doping, by the addition of special pre-fabricated nanometer sized normal conducting particles, or by radiation techniques. One particular strong point of the project is certainly the availability of new, highly localized characterization techniques that have been introduced by the Atomic Institute recently and which allow us to assess not only the global average of all supercurrents over the entire bulk pellet, but rather to monitor the local supercurrent flow on a sub-mm length scale, thus immediately indicating areas of weaker or stronger flux pinning. This information, together with standard structural characterizations of the pellets, is expected to lead to radical improvements in the material performance through immediate feedback with regard to the choice of the nano-scale defects and to the processing conditions.