THE FORMATION MECHANISM OF TEXTURED YBA2CU3O7-DELTA

The formation of textured YBa2Cu3O7-delta (123) from a liquid phase according to the peritectic reaction Y2BaCuO5 (211) + liquid --> 123 was analyzed using real-time analysis techniques of high-temperature X-ray diffraction, high-temperature optical microscopy, and environmental scanning electron microscopy (ESEM). Results were coupled with conventional "post-mortem" SEM analysis of processed samples at various stages of microstructural development. Observations of 123 formation and growth from the peritectic melt permit the conclusion that the presence of crystalline 211 primarily acts as a source of yttrium. The slow dissolution of 211 into the yttrium deficient liquid phase is the rate controlled step in the formation and growth of the textured 123, rather than its acting as a nucleation site for 123 grains as has been widely assumed.