Softening of Bi2212 crystals and growth mechanism of Bi2212 and Bi2201 grown at the KCl flux surface

A comparative study was carried out on observation of the growth mechanism of Bi2212 and Bi2201 crystals grown at the surface of a KCl flux by using o ptical microscopy and XRD. The growth of Bi2212 crystals is typically spira l mediated, while Bi2201 crystals are always layer-by-layer grown. We obser ved that the Bi2212 crystals grown on a KCI surface at 800-840 degrees C ar e soft and can be bent freely. No softening was observed for the Bi2201 cry stals. The generation of screw-dislocations can be caused by the coalescenc e of softened crystals. It is suggested that the formation of single, doubl e and multiple spirals in the Bi2212 crystals can be explained by the softe ning of the Bi2212 crystals. TEM studies revealed abundant dislocation netw orks in the softened Bi2212 crystals.