Cracking and oxygenation of YBaCuO bulk superconductors:: application to c-axis elements for current limitation

A process to elaborate crack free, oxygenated c-axis samples in YBa2Cu3Ox bulk superconductors is reported. This includes texturing of crack free pellets and development of an adequate oxygen annealing treatment to avoid cracking during oxygen uptake. For current limitation in c-direction such a process is needed as c-axis elements are particularly susceptible to ab-plane cracking during oxygenation. Mechanical properties have been compared for different annealing treatments by flexural strength measurements. With the load applied in ab-direction the mean flexural strength is 58 MPa in as-textured c-axis bars and 48 MPa in c-axis bars which were oxygenated using a customized annealing treatment. The conventional oxygen annealing treatments lead to macroscopic oxygenation cracks which reduced flexural strength to 10-20 MPa. Bars cut in ab-direction do not show significant variation in flexural strength (load applied in c-direction) as a function of the annealing condition with an average value of 145 MPa. (C) 2003 Published by Elsevier Science B.V.