Highly Textured and Single Crystal Bi sub 2 CaSr sub 2 Cu sub 2 O sub x Prepared by Float Zone Crystallization.

A CO sub 2 laser heat source was used to float zone 0.36 cm diameter ceramic rods of Bi sub 2 CaSr sub 2 Cu sub 2 O sub x. Well behaved, stable molten zones were obtained in air and in 1 atoms O sub 2 Highly textured elongated grains ~1 cm long with the c-axis normal to the rod axis were obtained at slow (0.19 cm/hr.) growth rates. Crystals 3x1.2x0.3mm were easily cleaved from such specimens. In the best cases (slow growth rates), x-ray powder diffraction indicated ~100% Bi sub 2 CaSr sub 2 Cu sub 2 O sub x, the superconducting transition temperature was as high as 87K, and diamagnetism measurements indicated 60-70% superconducting phase. Meissner measurements however, in common with most Meissner measurements on Bi-containing superconductors, indicated subtantially less superconductivity. Critical currents were comparable to untextured ceramic and flux grown single crystals. Float zoning shows great promise for preparing single crystals and textured ceramics of incongruently melting superconductors, even when detailed phase diagrams are not known.