Bulk processing and characterization of YBa2Cu306+x

Publisher Summary A variety of techniques have been used to make YBa 2 Cu 3 0 6+x (Y123) powder. Many are aimed at producing as fine a particle size as possible or achieving homogeneity on an atomic level. Despite the various advantages the different techniques have (fine particle size, well-controlled stoichiometry), when sintered the result is a sample with low critical current density and poor flux trapping at 77 K. This is a result of the weak links in the form of high-angle grain boundaries in polycrystalline samples. By processing the sample to produce an aligned microstructure with low-angle grain boundaries, however, the properties can be improved tremendously. Textured microstructures can be produced by directional solidification processes that exhibit transport J c values in excess of 10 5 A/cm 2 . The textured microstructure does not develop by the usual peritectic transformation, in this case the growth of 123 directly on 211 particles, but instead evolves by 123 nucleating homogeneously from the melt. Solidification models have been developed that indicate that the rate controlling step for the formation of 123 is 211 dissolution and diffusion of Y to the solidification front. Because commercialization of texturing is hindered by the required slow cooling rates, strategies must be devised to speed the 211 dissolution.