Enhancement of in-field current transport properties in GdBCO coated conductors by BaHfO₃ doping

We have investigated the in-field current transport property in BaHfO ₃ doped GdBa₂Cu₃O_7-δ coated conductors in a wide range of temperatures and magnetic fields. Significant improvement of in-field critical current I_c was observed, e.g., I_c@77 K,3T = 93A/cm-w, I_c@20 K 17T = 700 A/cm-w, which is a comparable value to that of Nb₃Sn wire at 4.2 K. Enhancement of the irreversibility field was also observed. These results suggest that BaHfO ₃ is one of the most promising materials as effective artificial pinning centers and leads to the enhancement of in-field I_c. Furthermore, we have also shown that our analytical expression of electric field versus current density characteristics based on the percolation transition model [1-3] agrees well with the experimental results over a wide range of magnetic fields and temperatures. This analytical expression is useful for the design of superconducting devices because this allows us to predict the current carrying capability of coated conductors not only J_c but also n-value at arbitrary operating conditions of temperature and magnetic field.