Effect of growth conditions on crystal morphology and superconductivity of Bi-2212 oxide

The effects of growth velocity and the nominal starting composition of the feed rod on the crystal morphology and stability of the solid-liquid interface in Bi-Sr-Ca-Cu-O high-T-c superconducting oxides were studied by a floating zone method. The result showed that an indispensable condition for the growth of large single crystals is that the solid-liquid interface maintains a stable planar growth front, The planar solid-liquid interface tends to break down into a cellular growth interface if the velocity is increased above 0.2 mm/h. The largest single crystals of size 20 x 5.5 x 1.5 mm(3), along the a-, b- and c-axes, respectively, were grown in 6.5 mm diameter rods. The superconducting transition temperature of the as-grown single crystals varies from 84 to 92 K under the different growth velocities and nominal compositions of a feed rod. The homogeneity of the superconducting phase of the crystals also depends on the growth conditions.