Decoupling and tuning competing effects of different types of defects on flux creep in irradiated YBa ₂ Cu ₃ O 7− δ coated conductors

YBa 2 Cu 3 O 7− δ coated conductors (CCs) have achieved high critical current densities ( 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 J c and reduce creep. CCs grown by metal organic deposition show non-monotonic changes in the temperature-dependent creep rate, S ( T ). Notably, in low fields, there is a conspicuous dip to low S as the temperature ( T ) increases from ∼20 to ∼65 K. Oxygen-, proton-, and Au-irradiation substantially increase 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 S ( 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 T A = 250 °C–600 °C. We observe a steady decrease in S ( T > 20 K) with increasing T A , unveiling the role of pre-existing nanoparticle precipitates in creating the dip in S ( T ) and point defects and clusters in increasing S at intermediate temperatures.