Possible degradation mechanism of BSCCO superconductors

A detailed study of the effect of ambient and humid atmosphere on the stability and physical properties of single and multiphasic samples of a BSCCO superconductor has been carried out. It has been observed that, on exposure to atmosphere for a period of one year, the single-phase samples 2223 or 2212 did not show any phase decomposition. However, a decrease in Tc was observed in these samples. Mixed-phase samples showed the partial conversion of the 2223 phase into the 2212 phase on the surface with a corresponding decrease in Tc, depending upon the initial amount of added Pb. X-ray photoelectron spectroscopy analysis of the multiphase, leaded samples showed the decrease in the ratio of Cu2+/Cu1+ as well as the formation of various surface carbonates responsible for the degradation in the superconducting parameters. In a humid atmosphere, a single-phase 2223 sample did not show any decomposition whereas single-phase 2212 or mixed-phase samples showed partial degradation to Bi2CuO4, SrCO3, CaCO3 and CuO as evidenced by X-ray diffraction and EDX analysis. Based on these observations a possible degradation mechanism has been proposed and the role of Pb has been discussed.