GROWTH OF SUPERCONDUCTING WHISKERS IN THE BI SYSTEM

The preparation and properties of Bi2Sr2CaCu2Ox (2212) and Bi2Sr2Ca2Cu3Ox (2223) superconducting whiskers are presented. The 2212 whiskers have been grown by annealing a melt-quenched glass plate in a stream of O2 gas. For the whisker growth, the glass precursor, Al addition to the glass, and a steady stream Of 02 are required. Each whisker, 2-10 mum thick, 10-500 Am wide and approximately 15 mm long, is composed of several plate-like single crystals which are stacked in a layered structure. The 2212 whiskers are flexible and are elastically bent up to a radius of curvature 0.2 mm corresponding to a bending strain of 0.5%. On the other hand, the 2223 whiskers have been prepared by a ''conversion by annealing in powder'' method (CAP method). They have been obtained by annealing the 2212 whiskers in a Ca- and Cu-rich Bi-Sr-Ca-Cu-Pb-O calcined powder. The appropriate annealing temperature is in the partial melting region of the calcined powder, as determined by DTA analysis. The phase conversion is brought about by diffusion of Ca and Cu into the 2212 whiskers from the liquid phase. The CAP method has been applied also to single crystals prepared by a flux method, resulting in 2223 sheet crystals as large as 1 mm2.