Effects of the sintering atmosphere on the superconductivity of   SmFeAsO1-xFx compounds
  A series of SmFeAsO1-xFx samples were sintered in quartz tubes filled with air of different pressures. The effects of the sintering atmosphere on the superconductivity were systematically investigated. The SmFeAsO1-xFx system maintains a transition temperature (Tc) near 50 K until the concentration of oxygen in quartz tubes increases to a certain threshold, after which Tc decreases dramatically. Fluorine losses, whether due to vaporization, reactions with starting materials, and reactions with oxygen, proved to be detrimental to the superconductivity of this material. The deleterious effects of the oxygen in the sintering atmosphere were also discussed in detail. 
Y. Ding, Y. Sun, X. D. Wang, J. C. Zhuang, L. J. Chui, Z. X. Shi
cond-mat.supr-con