Texture in Melt-Processed Bi-2212

The high temperature superconducting phaseBi2.2Sr2.055Ca0.95Cu2Ox (Bi-2212) decomposes peritectically when heated above itssolidus temperature and reforms during slow cooling from the partiallymolten state. In thick films of 60 µm the Bi-2212 grains grow directlyfrom the melt when cooled at a rate of 5 K/h in oxygen atmosphere. Theorientation of the nuclei in the melt is random. After nucleation the grainsgrow anisotropically, leading to a mica- or platelet-like morphology. Upongrowth the Bi-2212 platelets encounter several obstacles, i.e. the sampleboundaries, second phase grains and other platelets. Various reactions occurwhen their growth is hindered. They stop growing, change the direction ofgrowth or even grow through the obstacle. A mechanism is proposed whichallows small grains to turn themselves into a favorable orientation at theirinitial stage of growth. At the end of the partial melting process, thesemechanisms lead to a textured microstructure in thick films.