Growth, contacting and ageing of superconducting Bi-2212 whiskers

We report the growth of highly oriented microscopic whisker-like crystals in the Bi–Sr–Ca–Cu–O system by means of glassy precursors. The dependence of the growth on the stoichiometric composition and on the temperature and duration of the annealing process has been studied. Chemical impurities have been investigated from the point of view of the morphology, the elemental composition and the crystal structure, identifying the presence of CuAl 2 O 4 , Sr 1.2 Bi 0.8 O 3 and Al. Electrical contacts have been fabricated by means of thermal evaporation and diffusion. Their sizes have been carefully measured, achieving contact resistivity in the range of 0.2–3.7 × 10 −6 Ω cm 2 . A very slow degrading of the contacts and the crystals on a time scale of a few years has been detected. This is associated with a decrease in T c , which is probably due to oxygen release from the material.