CRYSTALLINE LINKAGE AND DEFECT STRUCTURES IN BULK ZONE MELT-TEXTURED YBA2CU3O7 OBSERVED BY TRANSMISSION ELECTRON-MICROSCOPY

The microstructural features of zone melt textured wires of YBa2Cu3O7 (123) with and without additions of Y2BaCuO5 have been examined by transmission electron microscopy. The 123 phase is observed to form well aligned platelets, which are of limited extent along [001], but extremely long in the perpendicular directions. Although platelet boundaries are wetted by a second phase, junctions are commonly observed to interconnect the plates. This suggests the possibility that the wires are actually highly defective single crystals. High densities of stacking faults are also observed, particularly at Y2BaCuO5/YBa2Cu3O7 interfaces and at dislocation arrays. It is suggested that these result from a drive for phase conversion to YBa2Cu4O8, and that they may be associated with flux pinning.