Natural and artificial low angle grain boundaries with high current-carrying capabilities

Abstract

For several years, the technical applications of bulk HTS YBCO superconductors are of growing interest. However, for applications which require a complex geometry of the monoliths, the Multi-Seeding Melt Growth (MSMG) and the mechanical joining of two single-domain tiles becomes necessary. However, these two techniques lead to the formation of a low-angle grain boundary (GB). The influence of the seed distance (d/sub s/) on the properties of the GB has been studied in order to obtain a precipitate free grain-boundary. On the top surface of one monolith, two distances between two seeds were chosen, i.e. 4 mm and 11 mm. Regarding d/sub s//spl sim/11 mm, some rich-copper phases and large pores can be observed throughout the GB. In contrast, for d/sub s//spl sim/4 mm, neither residual copper-rich phases nor pores are observed within the GB. Magneto-optical measurements performed on the sample with d/sub s//spl sim/4 mm, revealed that the critical current density through the GB is influenced by the growth directions. Regarding the mechanical joining, a high connectivity between two adjacent domains can be obtained by using the PLD technique for coating of the monoliths.