Influence of Na-doping and sintering temperature on increasing   Bi2Sr2CaCu2O8 superconducting phase content in powder form materials
  This paper proposes a systematic way to explore the effects of Na on Bi-2212 phase formation. The influence of sodium metal is correlated with the 2212 fraction formed in the sample. The effect on the sintering temperature and the importance of the substitution site is studied. Samples are characterized by X-ray diffraction analysis (XRD). Results clearly show that the 2212 phase content is enhanced and sintering temperatures can be lowered with regard to the undoped samples. 
S. Rahier, S. Stassen, R. Cloots and M. Ausloos