Microstructural studies of K₂CO₃ and Rb ₂CO₃ doped YBCO HTSC

The influence of Me₂CO₃ (Me = K or Rb) additions on the microstructural morphology of YBa₂Cu₃O_x (YBCO) HTSC with nominal composition Y_(1-0.2x)Ba _(2-0.2x)M_xCu₃O_y (x = 0-2.0) were investigated by means of orientation imaging microscopy which provides a method for measuring a large number of individual grain orientations and relating them directly to the microstructural features by means of evaluating electron backscatter Kikuchi patterns in scanning electron microscopy. We investigated the influence of the alkali additions on the grain orientation distributions of YBCO. The samples are characterized by grain orientation maps, and pole and inverse pole figures. Finally, the grain orientation distribution functions are obtained from the measured data. Within a certain range of doping (up to 5 wt.% in the initial batch), the grain sizes are found to increase as compared to pure YBCO, accompanied by an improvement of the superconducting properties (T_c). It is shown that the additions of alkali carbonates do not introduce any preferred grain orientations in YBCO HTSC in the entire doping range.