Tuning Vortex Creep in Irradiated YBa$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{7-\delta }}$ Coated Conductors
ORAL
Abstract
YBa$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{7-\delta }}$ coated conductors (CCs) show non-monotonic changes in the temperature-dependent creep rate, $S(T)$, due to mixed pinning landscapes comprised of twin boundaries, planar defects, point defects, and nanoparticle precipitates. Notably, in low fields, there is a conspicuous dip in $S$ as $T$ increases from $\sim $20K to $\sim $65K. The source of this dip is poorly understood. Moreover, pinning landscapes that are favorable for high critical currents, $J_{\mathrm{c}}$, are not necessarily optimal for low $S$. We have found that, though oxygen irradiation introduces few-nm-sized defects that result in significant increases in $J_{\mathrm{c}}$, it is detrimental to creep, increasing $S$ (reducing the dip depth) for $T>$20K. Understanding the source of this dip is crucial to engineering pinning landscapes that concurrently promote high $J_{\mathrm{c}}$ and low $S$. To this end, we study changes in $S(T)$ as we tune the ratio of smaller (point to few-nm-sized) defects to larger nanoparticles in an oxygen-irradiated CC by annealing in O$_{\mathrm{2}}$ at 250\textbf{\textdegree }C to 600\textbf{\textdegree }C. We observe a steady decrease in $S(T>$20K) with increasing annealing temperature. This suggests that pre-existing nanoparticle precipitates are likely responsible for the dip in $S(T)$, and underlines the fact that the effects of defects are not additive, but rather can be competitive.
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