Microstructural Analysis of YBCO Films Deposited by Advanced TFA-MOD Process

We have investigated the effects of the heating rate in the crystallization process on I_c values and microstructures of YBa₂Cu₃O_7-5 (YBCO) films, which were fabricated by the advanced metalorganic deposition(MOD) method using trifluoroacetates. As a result, it was found that the slow heating rate less than 2degC/min in the crystallization process increases the volume of randomly oriented YBCO crystals, which results in low I_c value of the YBCO film. Quenched samples were also prepared by heating at the various heating rates and cooling rapidly during the crystallization process. TEM observations of these quenched samples revealed that unreacted phase particles such as CuO, Y₂Cu₂O₅ and Ba-O-F crystallize and coarsen to large crystals before the nucleation and growth of YBCO crystals in the case of slow heating in the crystallization process. We found that it is important to control the sizes and distributions of the unreacted phase particles during the crystallization process as well as those in the calcination process, in order to fabricate the YBCO coated conductor with high I_c.