Study of Ageing and Fluctuation Effects in MgB 2 Superconductor

For device applications of a superconducting material, its stability to ambient conditions is an issue of critical concern. The study of the ageing effects of the recently discovered intermetallic compound MgB 2 is vital for knowing the degree of usefulness of this material. We report here the study of ageing and fluctuation conductivity behavior in bulk MgB 2 pellets and stainless-steel sheathed, in-situ synthesized MgB 2 tapes. A possible degradation mechanism is proposed based on ac-magnetic susceptibility and XRD investigations of MgB 2 samples exposed to ambient over prolonged durations of time. In addition, the fluctuation induced conductivity behavior is also analyzed based on the observed resistivity (ρ)-vs-T measurements in MgB 2 tape samples. This study indicated a three dimensional character of the MgB 2 with reasonably good estimates of coherence the length. The scaling of fluctuation induced conductivity enhancement is also investigated from the ρ(H) vs T data obtained for different applied field strengths. These findings support the three-dimensional nature of thermodynamic fluctuations operative in MgB 2 in contrast to that prevalent in several other high-temperature superconductors (HTSCs).