Characterization of natural and artificial low-angle boundaries in YBCO TSMG samples

Since several years, technical applications of bulk HTS YBCO superconductor s are of growing interest. However, shapes of HTS tiles needed for complex applications require the joining of two or more single-domain monoliths. Th e welding technique leads to the formation of a low-angle grain boundary an d then requires a high connectivity between two adjacent single-domain mate rials. This study was devoted to the characterization of the microstructure and the superconducting properties of natural and artificial low-angle gra in boundaries. The natural grain boundary formed during the multi-seeded me lt growth (MSMG) process exhibits a non-uniform microstructure during the g rowth. An energy dispersive spectroscopy (EDS) analysis carried out across the grain boundaries always reveals a depletion of copper and an accumulati on of yttrium. Mechanical joining of two single-domain monoliths leads to t he formation of an artificial grain boundary. This kind of joining was perf ormed either without or with a welding agent, i.e., YbBa2Cu3O7-x (Yb-123), The first method leads to a good connectivity between welded Y-123 platelet s. In contrast, the control of the mechanical welding process with a weldin g agent is more difficult. At 940 degrees C, Yb-123 decomposes into Yb2BaCu O5, BaCuO2 and CuO. This decomposition deteriorates the superconducting pro perties between two adjacent domains. (C) 2000 Elsevier Science B.V. All ri ghts reserved.