Development of high Jc Bi2223/Ag thick film materials prepared by heat treatment under low PO2

Abstract

In general, a dense and c-axis grain-oriented microstructure is desirable in order to achieve the high critical current properties of Bi2223 polycrystalline materials. On the other hand, our recent studies have shown that precise control of the chemical compositions of Bi2223 is also effective for the enhancement of intergrain Jc. In this study, the development of Bi2223 thick film materials with high critical current properties was attempted by controlling both the microstructure and the chemical compositions. A high intergrain Jc of ∼8 kA cm−2 at 77 K of a film with ∼40 μmt was achieved by increasing the Pb substitution level for the Bi site and controlling the nonstoichiometric chemical compositions. Furthermore, it was revealed that an increase in the thickness enabled us to obtain high Ic films suitable for practical applications. In contrast, there are still issues, especially in controlling the grain alignment at the inner part of the film, which suggests that the Jc properties of thick film materials could be further improved by forming a more ideal microstructure, as realized in the Bi2223 filaments of multi-filamentary Ag-sheathed tapes.