Abstract
Resistance measurements were performed on Bi2Sr2CaCu2O8+δ (Bi-2212) fabric-like nanowire networks or nanofiber mats in the temperature interval 3 K ≤T≤ 300 K. The nanowire fabrics were prepared by means of electrospinning, and consist of long (up to 100 μm) individual nanowires with a mean diameter of 250 nm. The microstructure of the nanowire network fiber mats and of the individual nanowires was thoroughly characterized by electron microscopy showing that the nanowires can be as thin as a single Bi-2212 grain. The polycrystalline nanowires are found to have a texture in the direction of the original polymer nanowire. The overall structure of the nanofiber mats is characterized by numerous interconnects among the nanowires, which enable current flow across the whole sample. The fluctuation-induced conductivity (excess conductivity) above the superconducting transition temperature, Tc, was analyzed using the Aslamzov-Larkin model. Four distinct fluctuation regimes (short-wave, two-dimensional, three-dimensional and critical fluctuation regimes) could be identified in the Bi-2212 nanowire fabric samples. These regimes in such nanowire network samples are discussed in detail for the first time. Based on this analysis, we determine several superconducting parameters from the resistance data.
Highlights
IntroductionHigh-Tc (HTSc) nanowires have been carried out on lithographically structured thin films [1,2]
Most studies of superconducting, high-Tc (HTSc) nanowires have been carried out on lithographically structured thin films [1,2]
We have presented an analysis of the microstructure of Bi-2212 nanofiber mat samples and a study of excess conductivity in these samples
Summary
High-Tc (HTSc) nanowires have been carried out on lithographically structured thin films [1,2]. In this way, it becomes possible to have control over the size and shape of the nanowire, but there is always an influence of the underlying substrate which cannot be ignored. The ceramic nature of the HTSc leads to specific growth modes of thin films [3], and the resulting current densities and flux pinning properties are clearly affected by stress/strain from the substrate [4], and largely different from single crystals. To optimize the superconducting properties of the HTSc nanowires, an additional oxygen treatment may be necessary
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