Transmission Electron Miscroscopy Observation of the Decomposition of YBa 2 Cu 4 O 8 into YBa 2 Cu 3 O 7-δ and CuO

The decomposition of Yba 2 Cu 4 O 8 (Y-124) into Yba 2 Cu 3 O 7-δ (Y-123) and CuO at high temperatures has been expected to create Y-123 with finely dispersed CuO precipitates suitable for flux pinning. In fact, samples 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 furnace annealed Y-124 were not suitable to clarify the reason for this J c enhancement. Nevertheless, the formation and growth of CuO precipitates have been observed by in situ decomposition of the Y-124 starting material due to electron beam heating within the TEM.