TRANSMISSION ELECTRON-MICROSCOPY OBSERVATION OF THE DECOMPOSITION OF YBA2CU4O8 INTO YBA2CU3O7-DELTA AND CUO

The decomposition of YBa2Cu4O8 (Y-124) into YBa2Cu3O7-delta (Y-123) an d CuO at high temperatures has been expected to create Y-123 with fine ly dispersed CuO precipitates suitable for flux pinning. In fact, samp les of thermally decomposed Y-124 exhibit a critical current density, J(c), which is enhanced with respect to the starting material as well as to pure Y-123. Transmission electron microscopy (TEM) studies of fu rnace annealed Y-124 were not suitable to clarify the reason for this J(c) enhancement. Nevertheless, the formation and growth of CuO precip itates have been observed by in situ decomposition of the Y-124 starti ng material due to electron beam heating within the TEM.