A Study on Oxygen Post-Annealing of GdBa₂Cu₃O_y Coated Conductors Irradiated with Low-Energy Ions

High-temperature superconducting coated conductors (CCs) based on REBa₂Cu₃O<i>_y</i> (REBCO, RE = rare earth) with high current carrying capacity are being developed for use in high magnetic field applications. For these applications, increasing critical current density <i>J</i>_c under magnetic fields is important considerations. The in-field <i>J</i>_c can be improved by the introduction of artificial pinning defects with nano-meter size, which can pin the vortices. The desired defect structures can be created by ion irradiation, which is a promising technique applicable to all superconducting materials. Depending on appropriate ion species and energy, ion irradiation enables the creation of a variety of defects, such as points, clusters and tracks in the materials. Recent studies show low-energy ion irradiation could be a viable option for creating uniform pinning defects in superconducting films^1-3). We have reported the effect of low-energy Au-ion irradiation on superconducting properties in GdBCO CCs. The superconducting transition temperatures <i>T</i>_c’s of the GdBCO films irradiated with 2 and 10 MeV Au-ions decrease gradually with increasing fluence up to around 8.0×10¹¹ ions cm^–2 and then significantly started to drop. The <i>J</i>_c in the GdBCO CCs irradiated with 10 MeV Au-ions shows over 70% enhancement at around 3 T and 30 K, indicative of effective pinning defects by the irradiation. In this talk, we will present a study on the oxygen post-annealing of GdBCO CCs irradiated with 2 and 10 MeV Au-ions. The oxygen post-annealing at 450 °C leads to a recovery of <i>T</i>_c, which is close to the pre-irradiation level up to 8×10¹¹ ions cm^–2 dose. We also observe an appreciable recovery of <i>T</i>_c above 8×10¹¹ ions cm^–2 dose, but these <i>T</i>_c values are much less than the one before the irradiation. These results indicate that the oxygen annealing is effective to restore the <i>T</i>_c of the GdBCO CCs irradiated 2 and 10 MeV Au-ions. We will present self-field and in-field <i>J</i>_c before and after the oxygen post-annealing in the irradiated GdBCO CCs. We will also report the effect of oxygen post-annealing temperature on superconducting properties of GdBCO CCs irradiated with 300 keV He-ions.<br/><br/>We would like to thank Sumitomo Electric Industries, Ltd. for providing the GdBCO CCs.<br/>Ion beam irradiation was performed at the Takasaki Ion Accelerators for Advanced Radiation Application (TIARA) of Japan’s National Institutes for Quantum Science and Technology (QST).<br/><br/>1) M. Leroux et al. Appl. Phys. Lett. 107, 192601 (2015)<br/>2) T. Ozaki et al., Supercond. Sci. Technol. 33, 094008 (2020).<br/>2) D. Huang et al., Supercond. Sci. Technol. 34, 045001 (2021).