Decoupling and tuning competing effects of different types of defects on flux creep in irradiated YBa${}_2$Cu${}_3$O${}_{7-\hat{I}´}$ coated conductors

Abstract

YBa${}_2$Cu${}_3$O${}_{7-\hat{I}´}$ coated conductors (CCs) have achieved high critical current densities (${\text{J}}_c$) 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 ${\text{J}}_c$ and reduce creep. CCs grown by metal organic deposition show non-monotonic changes in the temperature-dependent creep rate, $\text{S}(\text{T})$. Notably, in low fields, there is a conspicuous dip to low $\text{S}$ as temperature ($\text{T}$) increases from ~20 K to ~65 K. Oxygen-, proton-, and Au-irradiation substantially increase $\text{S}$ 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 $\text{S}(\text{T})$ 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 ${\text{T}}_A$ = 250$\hat{A}°$C to 600$\hat{A}°$C. We observe a steady decrease in $\text{S}$($\text{T}$ > 20 K) with increasing ${\text{T}}_A$, unveiling the role of pre-existing nanoparticle precipitates in creating the dip in $\text{S}(\text{T})$ and point defects and clusters in increasing $\text{S}$ at intermediate temperatures.

22 pages, 7 figures