  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.
