Synthesis and characterization of Bi2Sr2CaCu2O8 ceramics prepared in   presence of sodium
  This paper aims to study Na doping in Bi-2212 superconducting ceramics. Na-doped Bi-2212 samples powders with a Bi2-uSr2-vCa1-wCu2-xNayOz stoichiometry are prepared by means of thermal treatments. The intended Na substitution level, y, is fixed at 0.3. The initial content of the other ions is adopted so that Na substitution on one crystallographic site only is expected. Samples are characterized by electrical properties, X-ray diffraction analysis (XRD) and Energy Dispersive X-ray analysis (EDX). The influence of Na on the crystal chemistry and phases compatibility for 2212 materials is emphasized. Electrical resistivity results show that the critical temperature is independent of the sample initial stoichiometry. In some cases the production of a Bi-2223 phase is however enhanced. 
S. Rahier, S. Stassen, R. Cloots and M. Ausloos