INTERDENDRITIC SPACING AND VOLUME FRACTION OF SUPERCONDUCTING PHASES OF FIBERS GROWN BY THE LFZ METHOD

Superconducting fibers of Bi2Sr2Ca2Cu4O11 nominal composition were gro wn by laser floating zone technique (LFZ) at three pulling rates (R=1. 11x10(-6)m/s, R=2.22x10(-6)m/s and R=4.17x10(-6)m/s). All fibers are p olyphasic. The relative amount of each phase was quantified by stereol ogic measurements on SEM micrographs and by X-ray diffraction analysis . The volume fraction of superconducting phase ''2212'' decreased with the pulling rate as crystallization deviates from equilibrium The mea n interdendritic spacing between ''1/1'' primary dendrites lambda was measured on fiber cross sections, using lineal analysis. It decreases with R from 41 mu m to 26 mu m. Planar growth condition was identified from the planar instability criterion and the equality of lambda to t he edge-to-edge dendritic distance. Both methods of calculation lead t o a critical pulling rate close to 0.2x10(-6)m/s. (C) 1997 Academic Pr ess Limited.