Relative effects of Pb and Re doping in Hg-1223 thick films grown on Ag substrates

The relative effects of Pb and Re doping on microstructure, irreversibility field, and electronic anisotropy of HgBa₂Ca₂Cu₃O_8+δ (Hg-1223) thick films grown on Ag substrates prepared by dip-coating were studied. Both Pb- and Re-doped films exhibit the dominant phase of Hg-1223, characterized by a superconducting transition temperature (T _c) of 133 K. Both dopants distribute homogeneously in the Hg-1223 grains and promote grain growth. Pb-doped films have larger colony size compared to the Re-doped. The irreversibility fields (H _irr) of (Hg,Re)-1223 are significantly higher than those of (Hg,Pb)-1223 at temperatures below 100 K. The logarithmic plots of H_irr versus (1 - T/T_c) show both Pb- and Re-doped have a crossover temperature reflecting a transition from two- to three-dimensional behavior with increasing temperature. Re doping significantly decreases the electronic anisotropy γ, which would enhance flux pinning and consequently improve the critical current density. The differences between Pb and Re dopants in affecting γ are explained in terms of crystal structure.