MELT PROCESSING AND MORPHOLOGY OF FREEZE-DRIED YBA2CU3O7-X HIGH-TC SUPERCONDUCTORS

Although quench melt growth has been established as a suitable way to enhance the critical current density J(c) in bulk YBa2Cu3O7-x, reprodu cibility is difficult to guarantee. One way of eliminating the quench step, is to use starting powders consisting of an (Y2O3,Ba2Cu3Ox) mixt ure, which is a similar phase composition as is obtained after quenchi ng. These precursor powders can be produced by applying a freeze dryin g method, combined with an optimised calcination treatment. By applyin g a suitable melt-process, bulk YBa2Cu3O7-x can be obtained with a ran ge of different Y2BaCuO5 morphologies and a critical current J(c) at 7 7K of similar to 10(4) A/cm(2) in zero field and similar to 410(3) A/ cm(2) in a field of 3T. Quench experiments have been performed in orde r to determine the influence of holding time and composition on green phase content and morphology of stoichiometric Y1.2Ba2Cu3O7-x and YBa2 Cu3O7-x with 20 wt % Y2BaCuO5 excess compositions.