GROWTH AND MICROSTRUCTURE IN BI2SR2CACU2OY SINGLE-CRYSTALS

A flux technique involving a large temperature gradient is reported fo r the growth of superconducting Bi2Sr2CaCu2Oy, Bi2Sr2CuOy and doped Bi 2Sr2CaCu2Oy single crystals. We conclude that the cooling rate must be related to the crystal growth rate to obtain good quality crystals. W e present a model describing the geometrical configuration and Burgers vectors of dislocation networks observed in Bi2Sr2CaCu2Oy single crys tals. An orthorhombic-to-monoclinic phase transformation with associat ed (100) twinning has been observed by transmission electron microscop y in Bi2Sr2CaCu2Oy single crystals after heating in vacuum to between 350 and 400 degrees C. We propose that this transformation involves ox ygen diffusion through the CuO2 planes and subsequent oxygen vacancy o rdering.