HIGH-T-C SUPERCONDUCTING BI(AL)-CA-SR-CU-O GLASS-CERAMIC FIBERS DRAWN FROM GLASS PREFORMS

Bi(Al)-Ca-Sr-Cu-O glass-ceramic fibres over 100 cm in length were successfully drawn from a glass preform above the crystallization temperature, T-x. The diameters of the uniformly drawn fibres with circular cross-section could be controlled in the range from 25-200 mu m and the drawing speed was as high as 200 cm min(-1). In this work Al2O3 was used to modify the properties of the glass. It increased the glass transition and crystallization temperatures but did not significantly increase the glass working range. Shrinkage and increase of density during heat treatment of the glass fibres were observed. The annealed (825 degrees C/12 h in air) Bi4Al0.1Ca3Sr3Cu4Oy glass-ceramic fibre showed a T-c(onset) of 82 K and a T-c(zero) of 71 K.