Fabrication and characterization of Bi2223 tapes with interfilamentarySrZrO3+Bi2212 barriers for AC loss reduction

Abstract

To suppress interfilamentary coupling in(Bi,Pb)2Sr2Ca2Cu3Ox (Bi2223) multifilamentary tapes under an AC external magnetic field it is necessary toincrease the transverse resistivity by using a high-resistivity Ag alloy sheath as a matrix.Alternatively, oxide layers can be introduced as resistive barriers among the filaments,together with filament twisting. In this paper, we fabricated twisted Bi2223 tapeswith interfilamentary oxide barriers and evaluated the effect of the introductionof such a barrier on the AC magnetization loss properties in a perpendiculartransverse magnetic field. The conventional powder-in-tube method was used for tapefabrication. In order to avoid affecting the Bi2223 phase during the sintering process,SrZrO3 was selected as the barrier material. Moreover, 20 wt%Bi2Sr2CaCu2Oy (Bi2212) wasmixed with SrZrO3 to improve its ductility for cold working. Monocore Ag-sheathed rodswere coated with an oxide barrier using a slurry, before being stacked intohoneycomb structures. By twisting the filament with a twist pitch lengthbelow 9 mm and introducing interfilamentary barriers, the coupling frequency (fc) in a perpendicular field, which is inversely proportional to the decay time constant (τc) of coupling current, exceeded 100 Hz and perpendicular field losses around thepower-grid frequency were reduced from the analytical prediction for fully coupledfilaments. Avoiding physical connections among the irregular deformed filaments intwisted barrier tapes should lead to further loss reduction in a perpendicularfield.