Transport measurements and Jc simulations for RABiTS based coated conductors-doping and grain architecture

The critical current density in RABiTS (rolling assisted biaxially textured substrates) based coated conductors is limited by the network of small-angle grain boundaries up to a texture dependent crossover field H_co. The current flow through this network is percolative in nature and thus depends on misorientation angle distribution, the width and length of the tape, and on the grain shape. These dependencies were simulated using a fast and simple limiting path algorithm on real grain boundary networks obtained by electron backscattering diffraction (EBSD) and cross-checked with transport measurements. A strong dependence of J_c on conductor width below 20 grains and a large increase in J_c for elongated grains was found. H_co of tapes with very sharp cube textures are around 1 T at 77 K. Hence, the intra-grain pinning must be increased for a further improvement of coated conductors applied in higher magnetic fields. With transport measurements on YBa₂(Cu_1-xZn_x)₃O_7-δ single crystalline thin films, the possibility of a J_c increase due to Zn doping was investigated. Monolayer films with Zn contents up to 0.2%, however, showed a decrease in J_c and H_irr, whereas multilayer films with x=0.017% and x=0.025% Zn) showed an increase in J_c at 77 K.