Transport properties in Ca and Zn substituted NdBa₂Cu ₃O_7-δ single crystals

We have measured the transport properties in Ca and Zn substituted NdBa₂Cu₃O_7-δ (Nd123) single crystals grown by the travelling solvent floating zone (TSFZ) method. The normal state resistivity decreased with Ca doping and the electronic state changed into an over-doped state, which was revealed by the fact that the temperature dependence of resistivity turned into super-linear from the T-linear behavior. In contrast, a normal state resistivity increased with Zn doping presumably due to the fact that Zn acted as a scattering center. It was found that a combined addition of Ca and Zn was effective in increasing the irreversibility field and the critical current density simultaneously through the optimization of carrier concentration and pinning performance.