Doping effects of ZrO_2 nanoparticles on the superconducting properties of Bi-2212 tapes

摘要

Ag sheathed Bi-2212 single filament tapes with different content of ZrO_2 nanoparticles addition were fabricated with powder-in-tube process. X-ray diffractions were performed to examine the lattice structure and phase composition changes of these tapes. With the increase of ZrO_2 content, the lattice parameter c decreased, suggesting the change of chemical composition in Bi-2212 phase. Detectable Zr-containing particles can be observed in the tape with ZrO_2 content of 3.0 wt% in both XRD patterns and SEM images due to the saturation of Zr~(4+) irons in Bi-2212 matrix. The thermopower values at room temperature were measured to estimate the carrier concentrations. Attributed to the doping effect of Zr~(4+), the carrier concentration decreased due to the introduction of excess electrons. Meanwhile, the resistivity measured at room temperature increased and the carrier mobility decreased, suggesting the enhanced carrier scattering mechanism. Due to the change of superconducting properties with ZrO_2 doping, the current capacity of Bi-2212 tapes decreased. However, the (Ca, Sr)ZrO_3 precipitations with proper size, which can work as effective pinning centers enhanced the flux pinning properties of Bi-2212 tapes. Thus the tape with ZrO_2 content of 3.0 wt% regained the high current capacity under magnetic field and a higher J_c can be expected under the magnetic field higher than 25 T.