Effect of doping on evolution of He<sup>+ </sup>ion irradiation defects and superconductivity in EuBa<sub>2</sub>Cu<sub>3</sub>O<sub>7–δ</sub> superconducting strips

Rare-earth barium copper oxide (REBCO) as a representative of the second-generation high-temperature superconducting materials possesses superior physical advantages such as high critical magnetic field, elevated critical temperature, and superior current density, which has been applied to many domains. Although the introduction of non-superconducting nanoscale particle dopants, as a critical method, can enhance the magnetic flux pinning capability of REBCO strips, the effect of the doping on the performance change and microstructure evolution of the strips under irradiation is ignored. In this work, undoped and 3.5% BaHfO₃ (BHO) doped EuBa₂Cu₃O_7–δ strips are investigated in the room-temperature irradiation experiments (1.4 MeV He⁺ ions) with three distinct doses of 5×10¹⁴, 5×10¹⁵, and 5×10¹⁶ ions/cm², respectively. Electrical performance tests reveal that the undoped strips exhibit a slight increase in <i>J</i>_c after the low-dose irradiation. However, with dose increasing, <i>J</i>_c decreases by over 60%. In contrast, doped strips experience a significantly smaller decline in <i>J</i>_c, ranging only between 30% and 40% at high-dose irradiation. Raman spectroscopy and transmission electron microscopy characterizations confirm that the defects induced by He⁺ ion irradiation lead to amorphization and structural disorder within the superconducting layers, which is the primary reason for the decline in the superconducting properties of the strips. The results show that the introduction of localized strain through BHO nanophase in the superconducting layer changes the migration and aggregation behavior of irradiation-induced defects, repairing the damaged superconductor structure. Furthermore, the field dependence and temperature dependence of <i>J</i>_c of doped strips are irradiation-resistant due to BHO nanocrystals as strong pinning centers. Additionally, unlike the superconducting properties of the REBCO strips that can be repaired through oxygen annealing after neutron or heavy ion irradiation, the electrical properties of the two types of strips irradiated with high doses of He⁺ ions in this work are further deteriorated after being annealed. It is worth noting that compared with the undoped strip, the localized strain generated by BHO in the doped strip inhibits the size growth of helium defects in the three-dimensional direction at high temperatures, which changes the magnetic flux pinning characteristics and delays the disorder and amorphization of the superconducting layer structure caused by the severe growth of helium bubbles. This study provides a reference for the application of REBCO superconducting strips in the irradiation environment.