Critical Current Properties in $\hbox {REBa}_{2} \hbox {Cu}_{3}\hbox {O}_{y}$ Films With Nanorods Depending on Growth Conditions

Growth temperature (T_s) dependent microstructures of nanorods were clarified for BaNb₂O₆ (BNO)-doped YBa₂Cu₃O_y (Y123) films. The morphology of BNO in the Y123 matrix was changed from fluctuated nanorods to uniform nanorods with the increase in T_s. Reflecting this change in the nanorod morphology, spatial distribution of local critical current density (J_cl) determined from the percolation transition model became sharp with the increase in T_s. The sharp distribution of J_cl led to a steep slope of electric field vs. current density curve and a sharp J_c peak under B//c in the magnetic field angular dependence. The evaluation of the distribution of J_cl is a strong tool to understand quantitatively the relationship between the microstructure of nanorods and critical current properties for RE123 films with nanorods. To optimize the critical current properties under the magnetic field for RE123 coated conductors with nanorods, precise control of T_s is very important in the production process.