Effect of distribution of powder size on estimation of critical current densities in polycrystalline Sr0.6K0.4Fe2As2 superconductors

We prepared polycrystalline (SrK)Fe2As2 by one step solid state reaction method. According to addition of Ag, powder size increases. The apparent Jc is increased by increasing distribution of powder size. The local Jc is calculated with distribution of powder size. The local Jc is order of 1010 A/m2. The effect of distribution of powder size on the estimation of intra-grain critical current density was investigated for polycrystalline samples of Sr0.6K0.4Fe2As2 with and without addition of Ag 20 wt.%. It turned out that the value of intra-grain critical current density calculated using the average of powder size Jcl is more overestimated than that calculated taking account of the distribution of powder size JclP as the distribution of powder size is widened, since the magnetic moment drastically increases due to the larger contribution from larger particles. From the distribution of powder size obtained by the microscopic observation using SEM, the factor of overestimation of Jcl/JclP is found to be larger than two in both samples. Moreover, the distribution of powder size in the Ag-added sample is found to be smaller than that of pure sample. Therefore, the factor of overestimation of Jcl is considered to be smaller in the Ag-added sample. It is recommended to take account of the distribution of powder size for precise estimation of intra-grain critical current density.