LARGE SINGLE-CRYSTAL BI-2212 ALONG THE C-AXIS PREPARED BY FLOATING ZONE METHOD

A floating zone method was used to study the effects of the growth velocity and the starting compositions of the feed rod on the crystal growth behavior of Bi-2212. It shows that a necessary condition for obtaining large single crystals along the c-axis is that the solid-liquid interface of a rod maintains a smooth interface during crystal growth. A planar growth interface tends to break down into a cellular interface, while increasing the velocity from 0.2 mm/h, or white deviating from the optimum composition of Bi2.1Sr1.9Ca1.0Cu2.0Ox in a feed rod. Single crystals of up to 20 x 5.5 x 1.5 mm3 along the a-, b- and c-axes have been grown in a 6.4 mm diameter rod with optimum growth conditions. X-ray Laue measurements show that the quality of the single crystals is good. T(conset) is 91 K for as-grown crystals.