THE USE OF NANOPHASE POWDERS FOR HIGH J(C) SUPERCONDUCTOR TAPE PRODUCTION

Advances in processing of superconductors has demonstrated that cerami c powders with exact composition, super-homogeneity, and extremely fin e particle size can be prepared by chemical processing to achieve high density and uniform microstructure. The chemical processing routes ha ve great advantage in preparing powder with high reactivity thus promo ting solid state reactions required to produce 'purer' superconducting phase. We have studied extensively the coprecipitation technique for the preparation of superconducting ceramic powders. Chemical solution methods have been used in order to model several superconducting syste ms and to predict optimum conditions for obtaining exact composition. Several improvements on the control of precipitation reaction have bee n implemented in order to obtain powders of few nanometers in size. Th is has been done by carrying out the reaction in the bulk of a solutio n or in microemlusion systems. The corecipitated precursor powder has been used for production of 20-30 meter long Ag-clad tapes. These tape s require considerably reduced processing times. By controlled heat tr eatment conditions, these tapes have been processed to carry transport critical current density, J(c) > 4 x 10(4) A/cm(2) at 77K in zero app lied field.