酸化物バリアを導入した銀シースBi2223 線材の作製と評価

Abstract

Low AC loss Ag-sheathed Bi2223 tapes with oxide barriers among the twisted filaments were successfully fabricated using the powder-in-tube method. SrZrO3 was selected as the barrier material for its compatibility with Bi2223 oxide. Moreover, a small amount of Bi2212 was mixed with SrZrO3 to improve its ductility for cold working. By controlling barrier thickness and reducing the final tape width down to 2.7 mm, transport critical current densities Jc at 77 K and self-field attained 17-23 kA/cm2 for twisted barrier tapes with twist lengths Lt between 4 and 9 mm. For barrier tape with the shortest Lt = 4 mm, a coupling frequency fc , which is related to inverse of coupling time constant τc, of 270 Hz was attained in an AC transverse field perpendicular to a broader face of the tape. To our best knowledge, fc = 270 Hz under a perpendicular field is the highest ever reported value for Bi2223 tapes with self-field Jc > 15 kA/cm2 at 77 K. According to these achievements, perpendicular field losses around 50 Hz for barrier tape were 70-80% lower than those for conventional 4 mm-width tape with fully coupled filaments.