Decoupling and tuning competing effects of different types of defects on flux creep in irradiated YBa$_{2}$Cu$_{3}$O$_{7-δ}$ coated conductors

Abstract

YBa$_{2}$Cu$_{3}$O$_{7-δ}$ coated conductors (CCs) have achieved high critical current densities ($\textit{J}_{c}$) that can be further increased through the introduction of additional defects using particle irradiation. However, these gains are accompanied by increases in the flux creep rate, a manifestation of competition between the different types of defects. Here, we study this competition to better understand how to design pinning landscapes that simultaneously increase $\textit{J}_{c}$ and reduce creep. CCs grown by metal organic deposition show non-monotonic changes in the temperature-dependent creep rate, $\textit{S}(\textit{T})$. Notably, in low fields, there is a conspicuous dip to low $\textit{S}$ as temperature ($\textit{T}$) increases from ~20 K to ~65 K. Oxygen-, proton-, and Au-irradiation substantially increase $\textit{S}$ in this temperature range. Focusing on an oxygen-irradiated CC, we investigate the contribution of different types of irradiation-induced defects to the flux creep rate. Specifically, we study $\textit{S}(\textit{T})$ as we tune the relative density of point defects to larger defects by annealing both an as-grown and an irradiated CC in O$_{2}$ at temperatures $\textit{T}_{A}$ = 250$°$C to 600$°$C. We observe a steady decrease in $\textit{S}$($\textit{T}$ > 20 K) with increasing $\textit{T}_{A}$, unveiling the role of pre-existing nanoparticle precipitates in creating the dip in $\textit{S}(\textit{T})$ and point defects and clusters in increasing $\textit{S}$ at intermediate temperatures.