Fabrication of melt-textured cylinders and bars of (YBa2Cu3O7-Y2BaCuO5) superconductors

Cylinders and bars of bulk YBa2CuO7-Y2BaCuO5 textured ceramic composites (123-211) have been prepared through different directional solidification processes. Green ceramic preforms for the directional solidification process have been obtained by sintering the starting powders (123) and (211) in ceramic moulds at small pressures and by using a Cold Isostatic Pressing technique (CIP). The bars were melted and solidified in a vertical gradient furnace by the Bridgman technique at different rates up to 5mm/h. Cylinders were melted and solidified at 1-2ºC/h using single crystal seeds of different materials at different vertical gradients. We have studied the influence of (123)/(211) ratios, additions, particle size of the precursors and thermal treatments. The complex microstructure of these ceramic composites has been investigated by SEM, TEM and optical microscope. The directional solidification process allows to obtain quasi-single crystal superconductors with critical currents above 105A/cm2 at 77k and zero field.