Improvement in granularity of NdFeAsO0.8F0.2 superconductor through Agx doping (x = 0.0-0.3)

We report the impact of silver addition on granularity of NdFeAsO0.8F0.2 superconductor. The ac susceptibility and electrical resistivity under magnetic field are measured to study the improvement in weak links of NdFeAsO0.8F0.2 with addition of Agx (x = 0.0-0.3). The Ag free NdFeAsO0.8F0.2 compound shows superconductivity at around 51.8 K. Typical two step superconducting transitions due to the inter- and intra-grain contributions, induced from the combined effect of superconducting grains and the inter-granular weak-coupled medium respectively are clearly seen in susceptibility [χ(T)] plots. In comparison to the pure NdFeAsO0.8F0.2 compound, the coupling between the superconducting grains is significantly improved for 20 at% silver doped sample, and the same is deteriorated for higher Ag content i.e., for 30 at%Ag sample. The magneto transport measurements ρ(T)H of polycrystalline 20 at% Ag doped NdFeAsO0.8F0.2 exhibited the upper critical filed [Hc2(0)] of up to 334 T, which is slightly higher than the one observed for pure NdFeAsO0.8F0.2. The flux flow activation energy (U0/kB) varies from 7143.38 K to 454.77 K with magnetic field ranging from 0 T to 14 T for 20 at% Ag doped NdFeAsO0.8F0.2. In this investigation, our results show that limited addition of Ag improves the granular coupling of superconducting grains of NdFeAsO0.8F0.2 compound.