Transport measurements and J/sub c/ 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/sub 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/sub c/ on conductor width below 20 grains and a large increase in J/sub c/ for elongated grains was found. H/sub 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 YBa/sub 2/(Cu/sub 1-x/Zn/sub x/)/sub 3/O/sub 7-/spl delta// single crystalline thin films, the possibility of a J/sub c/ increase due to Zn doping was investigated. Monolayer films with Zn contents up to 0.2%, however, showed a decrease in J/sub c/ and H/sub irr/, whereas multilayer films with x=0.017% and x=0.025% Zn) showed an increase in J/sub c/ at 77 K.