Effect of post-annealing on the pinning properties of GdBa₂Cu₃O_7-δ coated conductors prepared by RCE-DR

The pinning properties of GdBa₂Cu₃O_7-δ (GdBCO) films fabricated by the reactive co-evaporation deposition and reaction (RCE-DR) process were very sensitive to the post-annealing temperature in a reduced oxygen atmosphere. For this study, as-grown GdBCO coated conductors (CCs) were post-annealed at the temperatures ranging from 450 to 750 °C in the oxygen pressure (PO₂) of 300 mTorr, and subsequently oxygenated at 500 °C for 1 h in pure oxygen gas atmosphere. Compared with the pristine sample, samples post-annealed at the temperature region of 450 °C–600 °C for 1 h possessed higher stacking fault (SF) density and also included the GdBa₂Cu₄O₈ (Gd124) phase while samples post-annealed at 650 °C for 1 h and 750 °C for 5 min showed lower SF density. The HAADF-STEM analyses on the sample post-annealed at 500 °C revealed that the Gd124 phase mainly existed near the CuO phase. At the temperature region of 50–77 K, while the minimum in-field critical current densities (J_c,min) of as-grown GdBCO CC were enhanced in relatively higher fields after post-annealing at 750 °C due to reduced SF density, both J_c ^ab and J_c,min values were increased after post-annealing at 500 °C in relatively lower fields due to both increased SF density and the formation of Gd124. (paper)