| YBa2Cu3O7−x (123) high temperature superconducting powders were synthesized by mixing Y2O3, CuO, and BaCO3 precursor powders and subsequently reacting them at 920°C in a rotary calciner. The effects of carbon on the critical temperature (Tc), critical current density (Jc), trapped field, as well as the growth of melt textured 123 single crystals were examined as a function of the extent of calcination. Increasing carbon content in the sample resulted in lower and broader transition temperatures, however, J c's were improved showing a high field “fishtail” effect at 77K. Highly porous microstructure were, however, formed with increasing carbon content, thus degrading the properties of the material.; To further improve Jc density, non-volatile substitutional and secondary phase dopants were utilized. The addition of 1 wt% CeO 2 (secondary phase particulate) led to an approximate 35% increase in Jc by the formation of ∼1μm BaCeO3 inclusions. Liquid loss was consequently reduced from the CeO2 additions due to increased capillary forces in the semi-solid melt. Nd2O 3 (substitutional dopant) not only substitutes yttrium lattice sites, but also barium lattice sites which can effectively kill superconductivity in a local regions, creating very small flux pinning sites. Additions of less than 0.1mol% Nd2O3 have shown improved high field J c's, however, Nd2O3 additions beyond 1mol% are deleterious to crystal growth due to the formation of Nd123, a higher melting point perovskite, resulting in polycrystalline crystal growth.; YBa2Cu3O7−x growth kinetics have been examined to determine factors that may effect particle pushing/entrapment. These factors, such as critical particle radius, critical interface growth velocity, and interfacial energy contributions, are essential for the processing of melt textured single crystals with homogeneous distributions of fine secondary phase dopants. Melt textured single crystals have been grown utilizing an off axis [100] seed which clearly shows Y2BaCuO5 segregation in the a–b vs. c growth sectors under slow growth conditions. Solidification mechanisms and kinetics for each a–b and c-growth sectors will be discussed in context of microstructural development. |
