  The tetragonal FeSe phase is an intensively investigated iron based
superconductor. In this study we examined the influence of Ag addition on the
superconducting properties of selenium deficient polycrystalline FeSe0.94. The
samples were obtained by solid state reaction and melting methods. XRD analysis
shows the presence of tetragonal phase and EDX analysis establishes
inhomogeneous Ag distribution in the grains. The superconducting properties
were investigated by fundamental and third harmonic AC magnetic susceptibility.
The intergranular critical current determined from AC magnetic susceptibility
in the Ag doped sample is several times higher than that in the undoped one,
obtained by melting at approximately the same temperatures. Intra-granular
current is field independent up to almost 1000 Oe. Using the temperature
dependence of third harmonic AC magnetic susceptibility at different DC
magnetic fields, the irreversibility lines were obtained for all samples. It is
found that Ag addition increased the irreversibility field in comparison with
undoped melted and powder sintered samples. All results show that the Ag
addition in selenium deficient (FeSe0.94) samples leads to improvement of
inter- and intra- granular properties: screening ability, pinning, activation
energy and critical current and improves the irreversibility line.
