  We have investigated the effects of lead (Pb) additions (x) up to 40 wt.% (x
= 0-0.4) on the structure, electrical properties, and magnetic properties of
FeSe0.5Te0.5 superconductor. The samples were prepared by the solid-state
reaction method and characterized by various techniques. The parent compound (x
= 0) showed the onset temperature Tc onset of 15 K, and zero-resistance
temperature, Tc offset of 12 K. The addition of Pb enhances the metallic
characteristics of FeSe0.5Te0.5, but both Tc onset and Tc offset are decreased
to the lower temperature with the broadened transition width. The Tc onset is
nearly the same (10.3 K) at higher additions, such as x = 0.3 and 0.4, but zero
resistivity is not observed up to 7 K. Microstructural analysis and transport
studies suggest that for x > 0.05, Pb additions weakened the coupling between
grains and suppressed the superconducting percolation, leading to a broad
transition. More importantly, the inclusion of a relatively small amount of Pb
(x = 0.05) increased the critical current density, Jc, in the entire magnetic
field, which might be attributable to better phase uniformity as well as good
grain connectivity.
