FORMATION OF COLONIES OF LOCALLY ALIGNED GRAINS DURING THALLINATION OF SPRAY-PYROLYZED BA2CA2CU3OX THICK-FILMS

Recent microstructural studies of high-J(c) Tl-1223, spray-pyrolyzed t hick films have shown that the high J(c) and reduced weak-link behavio r can be ascribed to the presence of a unique microstructure, wherein the film is divided into ''colonies'' of biaxially aligned regions. In an effort to understand the nucleation and growth of Tl-1223 as well as the formation of the ''colony'' microstructure, several sets of fil ms quenched from various stages of the high-temperature tballination p rocess were examined using electron microscopy, X-ray diffraction and Electron backscatter diffraction (EBSP). It is found that the crystall ization of the 1223 phase is associated with formation of a liquid pha se which contains significant amounts of all oxides, X-ray micro-diffr action measurements show that the 1223 phase crystallizes in an aligne d manner. Studies of films very early into the thallination process sh ow that local biaxial alignment or the formation of colonies starts to occur at the onset of 1223 crystallization. In addition, it appears t hat the structure within colonies is a function of tile processing con ditions employed. This presents the possibility for further optimizati on of the microstructure to attain improved superconducting properties .