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

TL;DR

This study explores how different irradiation-induced defects affect flux creep in YBa₂Cu₃O₇-δ coated conductors, aiming to optimize defect landscapes for high critical current density and low creep.

Contribution

It demonstrates how tuning defect types and densities via irradiation and annealing influences flux creep behavior, providing insights for designing improved superconducting materials.

Findings

Irradiation increases flux creep rate in certain temperature ranges.

Annealing modifies defect landscape, reducing creep rate at higher temperatures.

Pre-existing nanoparticle precipitates and point defects have contrasting effects on flux creep.

Abstract

YBa$_{2}$Cu$_{3}$O$_{7-{\delta}}$ 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${\deg}$C to 600${\deg}$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.