Influence of Ag₂O addition on thermal conductivity of (Nd-Eu-Gd)Ba₂Cu₃O_y

The influence of the Ag₂O addition on the thermal conductivity κ of (Nd-Eu-Gd)Ba₂Cu₃O_y melt-textured superconductors with several amounts of NEG-211 phase has been studied. The concentration of added Ag₂O is up to 20 wt.%. The distribution of Ag was observed by back electron image. The critical current density evaluated from a magnetization measurement increases with Ag₂O at higher magnetic field, which suggests the precipitation of light rare earth (LRE)-rich fine clusters. It was found that the thermal conductivity below T_c might be determined by the phonon scattering by the LRE-rich fine clusters, which suppress the enhancement of κ, and by the improvement of the crystallographic quality with Ag-doping, by which the enhancement is recovered. In almost all of the samples we measured the latter was dominant. The suppression of κ by the magnetic field H was observed below 110 K. The ratio of κ(H)/κ(H = 0) is almost independent of the amount of Ag₂O content.