Melt processing and morphology of freeze dried YBa 2Cu 3O 7-x high Tc superconductors

Abstract

Although quench melt growth has been established as a suitable way to enhance the critical current density J c in bulk YBa 2Cu 3O 7-x, reproducibility is difficult to guarantee. One way of eliminating the quench step, is to use starting powders consisting of an (Y 2O 3, Ba 2Cu 3O x) mixture, which is a similar phase composition as is obtained after quenching. These precursor powders can be produced by applying a freeze drying method, combined with an optimised calcination treatment. By applying a suitable melt-process, bulk YBa 2Cu 3O 7-x can be obtained with a range of different Y 2BaCuO 5 morphologies and a critical current J c at 77K of ∼ 10 4 A/cm 2 in zero field and ∼4∗10 3 A/cm 2 in a field of 3T. Quench experiments have been performed in order to determine the influence of holding time and composition on green phase content and morphology of stoichiometric Y 1.2Ba 2Cu 3O 7−x and YBa 2Cu 3O 7−x with 20 wt% Y 2BaCuO 5 excess compositions.