Distinctive microstructures of textured YBa2Cu3Ox (123) superconductors were examined by scanning electron microscopy and metallurgical microscopy. The samples were synthesized under a residual thermal gradient by using a modified melt textured growth on a Y2BaCuO5 (211) substrate. Also, the unidirectional solidification by a zone‐melting method was performed to fabricate 123 superconducting bars up to 12 cm long placed on the 211 substrate in the horizontal arrangement, with a growth rate R=0.5 mm/h and a temperature gradient of G=20 °C/cm (G/R=400 °C h/cm2). A ramping temperature of 1 °C/h (GR) was applied in both syntheses. Typical defects running parallel to (001) planes associated with 211 trapped particles were observed (so‐called platelet structure). Besides these, unusual defects were observed running parallel to (100) and (010) planes in textured 123+Pt superconductors, and interpreted as the result of an instability of the planar front in the presence of fine 211 particles. A theoretical model of planar interface stability confirms a strong dependence of stability region on the size of 211 particles in the melt.
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Copyright © 1995, American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters 67.2, and may be found at http://apl.aip.org/resource/1/applab/v67/i2/p288_s1?isAuthorized=no.