Oxygen determination from cell dimension in YBCO superconductors

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 stoicheiometric 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, of the elemental composition and of the crystal structure, identifying the presence of CuAl2O4, Sr1.2Bi0.8O3 and Al. Electrical contacts have been fabricated by means of thermal evaporation and diffusion and their sizes have been carefully measured, achieving contact resistivity in the range 0.2–3.7 × 10−6 cm2. A very slowdegrading of the contacts and of the crystals on a few years’ time scale has been detected, associated to a decrease in Tc, probably due to oxygen release from the material.