  The superconducting properties of polycrystalline Sr0.6K0.4Fe2As2 were
strongly influenced by Ag doping (Supercond. Sci. Technol. 23 (2010) 025027).
Ag addition is mainly dominated by silver diffusing, so the annealing process
is one of the essential factors to achieve high quality Ag doped
Sr0.6K0.4Fe2As2. In this paper, the optimal annealing conditions were studied
for Ag doped Sr0.6K0.4Fe2As2 bulks prepared by a one-step solid reaction
method. It is found that the annealing temperature has a strong influence on
the superconducting properties, especially on the critical current density Jc.
As a result, higher heat treatment temperature (~900C) is helpful in diffusing
Ag and reducing the impurity phase gathered together to improve the grain
connectivity. In contrast, low-temperature sintering is counterproductive for
Ag doped samples. These results clearly suggest that annealing at ~900C is
necessary for obtaining high Jc Ag-doped samples.
