Suppression of vortex channeling in meandered YBa2Cu3O7−δ grain boundaries

Abstract

We report on the in-plane magnetic field (H) dependence of the critical current density (Jc) in meandered and planar single grain boundaries (GBs) isolated in YBa2Cu3O 7−δ (YBCO) coated conductors. The Jc(H) properties of the planar GB are consistent with those previously seen in single GBs of YBCO films grown on SrTiO3 bi-crystals. In the straight boundary a characteristic flux channeling regime when H is oriented near the GB plane, associated with a reduced Jc, is seen. The meandered GB does not show vortex channeling since it is not possible for a sufficient length of vortex line to lie within it.

Critical Current Densities of Isolated Grain Boundaries in Coated Conductors

“…At fields from 1 T upwards we observe a minimum in critical current density at which corresponds exactly to the orientation where the bridge is perpendicular to the field. Meandering of GBs prevents vortex channeling along the boundaries [13] which would be expected for planar boundaries [8]. We therefore conclude that for at angles around the minimum the critical current is limited by pinning in the neighboring grains, rather than by the properties of the isolated grain boundary [23].…”

“…Secondly, it was discovered that certain ex situ growth methods lead to meandering GBs (both along their length and through the thickness) [14], [15], which show a higher than planar boundaries [12]. This increase has been explained by their larger cross sectional area [12], [16] and by the suppression of vortex channeling along the boundaries [13].…”

“…Most of this work has been done using model systems consisting of YBCO thin films grown on bicrystal substrates [1], [2], [6], [8], [11] and only recently data obtained on isolated CC grain boundaries has been published [4], [12], [13]. Manuscript Whereas useful and important insights have been made using bicrystals, studying GBs on coated conductors is essential for two reasons.…”

Importance of low-angle grain boundaries in YBa2Cu3O7−δcoated conductors

“…Gray et al [94] noted that atomically flat bulk bi-crystal boundaries exhibit a depressed critical current when compared to equivalent misorientation angles in meandered boundaries in thin film bi-crystals. In a similar manner as to the proposed mechanism for the enhancement of MOD GBs over PLD GBs, the difference between bulk and thin film grain boundaries may well be due to the partial suppression of easy vortex motion at the boundary as the vortex cannot lie entirely within the weakly pinned boundary [95].…”

“…The nature of these elements on a microstructural level can vary greatly depending on which of a wide range of processing routes are chosen. Furthermore these elements have different [30,100] and complex [95,85,15] dependencies on temperature and also the magnitude and orientation of magnetic field. We can only satisfactorily describe and explain the overall electromagnetic properties of a coated conductor if we understand the Processing -Structure -Properties relationship at a microscopic level and can recognise how the properties of the individual elements combine to determine the performance of macroscopic superconducting tapes developed for large-scale applications.…”