Influence of the grain boundary network on the critical current density of deformation-texturedYBa2Cu3O7−xcoated conductors made by metal-organic deposition

Abstract

Coated conductors (CC) are quasisingle crystals consisting of a series-parallel network of predominantly low angle grain boundaries, whose network misorientation distribution determines the current-carrying characteristics. To deepen our understanding of the influence of the grain boundary network in CC, we present a study of critical current density $({J}_{c})$ and electric field--current density $(E\text{\ensuremath{-}}J)$ characteristics over a broad range of magnetic fields and temperatures in a series of three 1-\ensuremath{\mu}m-thick ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\text{\ensuremath{-}}x}$ samples with variable textures, including a single-crystal film and two deformation-textured coated conductors made by a metal-organic deposition (MOD) process. We also investigated the influence of the number of grains within the bridge width by successively narrowing the bridge on the better-textured CC. We found clear evidence of crossover from grain boundary (GB) network control to grain control of ${J}_{c}$ by study of the magnitude of ${J}_{c}$ and the shape of the $E\text{\ensuremath{-}}J$ characteristic. In the narrowest tracks, we were able to isolate the effect of single GBs, finding dissipation only when the misorientation exceeded $\ensuremath{\sim}7\ifmmode^\circ\else\textdegree\fi{}$, more than twice that seen in classic bicrystal experiments. We found that the influence of global texture on ${J}_{c}$ (77 K, 0 T) is highly nonlinear, ${J}_{c}$ rising by more than 2.5 times as the full width at half maximum decreases only by $\ensuremath{\sim}2\ifmmode^\circ\else\textdegree\fi{}$. Very interestingly, the MOD-CC exhibited no grain boundary dissipation signature in their $E\text{\ensuremath{-}}J$ characteristics in wide bridges, showing that global influence of grain boundary network is very much attenuated even for the grain boundary network containing misorientations that would generate significant dissipation in thin film bicrystals.