Processing, microstructure and characterization of artificial joins in top seeded melt grown Y-Ba-Cu-O

A technique based on the presence of an unreacted barium-cuprate phase within the melt-processed microstructure (predominantly at the platelet boundaries), which melts below the peritectic temperature of the YBa2Cu3O7-delta (Y123) phase has been developed to join large Y-Ba-Cu-O (YBCO) grains. On heating under an applied pressure of 0.1 MPa, the Ba-Cu-O liquid phase is released to the grain interface. This technique has been investigated for YBCO a-b-plane-aligned grain boundaries with misorientation angles of up to 45degrees and an aligned c-axis grain boundary. Optical and transmission electron microscopy studies indicate that the low-angle a-b plane grain boundaries are epitaxial in nature and are generally of high microstructural quality. The electrical and magnetic properties of the grain boundaries fabricated by this technique have been characterized by I-V and transport current measurements as a function of magnitude and orientation of the applied field. The temperature dependence of the irreversibility field of low-angle a-b grain boundaries is similar to that of the grains, providing direct evidence for the quality of the join. A join of nominally zero misorientation between the a-b planes was found to support a critical current density, J(c), exceeding 2000 A cm(-2) at 77 K in fields of up to 4 T.