A NEW METHOD FOR NET-SHAPE FORMING OF LARGE, SINGLE-DOMAIN YBA2CU3O6+X

A new process has been developed for the net-shape fabrication of bulk , single-domain YBa2Cu3O6+x (123) specimens. To date, transport critic al currents in excess of 10 000 A cm-2 have been obtained. This proces s, designated the seeded preform (SPF) technique, involves the permeat ion of peritectic liquid through a preform of pressed Y2BaCuO5 (211) p owder. The use of a single-crystal seed of Nd1+xBa2-xCu3O(y), ensures that only a single 123 domain is nucleated during the subsequent trans formation: liquid + 211 --> 123. The SPF process enjoys several import ant advantages over the melt-texturing techniques which are currently available. In particular, it offers the potential of net-shape forming of bulk 123 samples with complex geometries, and circumvents problems such as sagging, and substrate reaction. Also unique to the SPF proce ss is that it produces large, single domain 123, with essentially no e ncapsulated liquid phase. Finally, relative to conventional melt-textu ring, there is a refinement of the size of the 211 inclusions in the f inal microstructure, and the particles are more uniformly distributed.