  The properties of the grain boundaries (GBs) are of significant importance in
high-Tc cuprates. Most large scale applications of cuprate superconductors
involve usage of sintered compounds. The critical current density and the
ability to trap high magnetic flux inside the sample depend largely on the
quality of the GBs. Zn has the ability to pin vortices but it also degrades
superconductivity. In this study we have investigated the effect of Zn impurity
on the intergrain coupling properties in high-quality La2-xSrxCu1-yZnyO4
sintered samples with different hole concentrations, p (\equiv x), over a wide
range of Zn contents (y) using field-dependent ac susceptibility (ACS)
measurements. The ACS results enabled us to determine the superconducting
transition temperature Tc, and the temperature Tgcp, at which the randomly
oriented superconducting grains become coupled as a function of hole and
disorder contents. We have analyzed the behavior of the GBs from the systematic
evolution of the values of Tgcp(p, y), Tc(p, y), and from the contribution to
the field-dependent ACS signal coming from the intergrain shielding current. Zn
suppresses both Tc and Tgcp in a similar fashion. The hole content and the
carrier localization due to Zn substitution seem to have significant effect on
the coupling properties of the GBs. We have discussed the possible implications
of these findings in detail in this article.
  PACS: 74.72.Dn; 74.62.Dh; 74.25.Sv Keywords: Zn doped La214; Critical current
density; Grain boundary
