GROWTH AND CHARACTERIZATION OF BI-SR-CA-CU-O SUPERCONDUCTING FIBERS

With the laser-heated floating zone method, fibers of nominal overall composition Bi2Sr2CaCu2O8+/-z and Bi2Sr2Ca2Cu3O10+/-z have been grown. Fibers of uniform diameter up to approximately 1 cm long have been produced. The influence of the growth rates and feed rod compositions on the microstructure of grown fibers were determined with XRD, SEM, EDS, and resistive T(c) measurements. At 5 mm/h growth rate, compositionally homogeneous material can be grown from the 2212 composition over a length of several hundred mu-m. Fibers grown at higher rates consist predominantly of Bi2+x(Sr,Ca)(2-x)CuO6+/-z (the 25 angstrom phase) with smaller amounts of Bi2(Sr,Ca)3Cu2O8+/-z (the 31 angstrom phase) and (Sr,Ca)CuO2 phases. These multiphase fibers show a resistive superconducting transition at 80K. After annealing at 800-degrees-C for 12 hrs in air, the proportion of the 31 angstrom phase is increased, the normal state resistivity is decreased, and the T(c) rises to 90K.