The microstructures of textured samples of the superconductor were examined by means of scanning electron microscopy and metallography. The samples were synthesized in a residual thermal gradient by modified melt-textured growth on a Y2BaCuO5 substrate. Also, unidirectional solidification via zone-melting was used to fabricate Cu3Ba2YOx bars at a growth rate of 0.5mm/h in a temperature gradient of 20C/cm. A temperature ramp of 1C/h was used in both cases. Defects which ran parallel to (100) planes, and which were associated with trapped particles of Y2BaCuO5, were observed (platelet structure). Unusual defects were also observed which ran parallel to the (100) and (010) planes in textured Cu3Ba2YOx+Pt superconductors. These were suggested to be the result of an instability of the planar front in the presence of fine Y2BaCuO5 particles. A theoretical model for planar interface stability confirmed that there was a strong dependence of the stability region upon the size of the Y2BaCuO5 particles in the melt.

G.Kozlowski, T.Svobodny: Applied Physics Letters, 1995, 67[2], 288-90