  We have prepared a series of (FeSe0.5Te0.5 + xGd) bulk samples, with x = 0,
0.03, 0.05, 0.07, 0.1 and 0.2, through the convenient solid-state reaction
method at ambient pressure (CSP). High gas pressure and high-temperature
synthesis methods (HP-HTS) are also applied to grow the parent compound (x = 0)
and 5-wt% of Gd-added bulks. Structural, microstructural, transport and
magnetic characterizations have been performed on these samples in order to
draw the final conclusion. Our analysis results that the HP-HTS applied for the
parent compound enhances the transition temperature (Tc) and the critical
current density (Jc) with the improved sample density and intergrain
connections. The lattice parameter c is increased with Gd additions, suggesting
a small amount of Gd enters the tetragonal lattice of FeSe0.5Te0.5 and the Gd
interstitial sites are along the c-axis. A systematic decrease of the onset
transition temperature Tc is observed with Gd additions, however, the
calculated Jc of these Gd-added samples is almost the same as that of the
parent compound prepared by CSP. It specifies that there is no improvement of
the grain connections or pinning properties due to these rare earth additions.
However, Gd-added FeSe0.5Te0.5 bulks prepared by HP-HTS have revealed a
slightly improved critical current density due to improved grain connections
and sample density but have a lower transition temperature than that of the
parent compounds.
