The Performance of the Two-Seeded GdBCO Superconductor Bulk with the Buffer by the Modified TSMG Method

Abstract

The multiseeding technique is a method to grow large-sized REBa₂Cu₃O_7-δ (REBCO, where RE is a rare earth element) high temperature superconducting bulks. However, due to the existence of grain boundaries between seed crystals, the superconducting properties of bulks are not always better than those of single grain bulks. In order to improve the superconducting properties caused by grain boundaries, we introduced buffer layers with a diameter of 6 mm in the growth of GdBCO bulks. Using the modified top-seeded melt texture growth method (TSMG), that is, YBa₂Cu₃O_7-δ (Y123) as the liquid phase source, two GdBCO superconducting bulks with buffer layers with a diameter of 25 mm and a thickness of 12 mm were successfully prepared. The seed crystal arrangement of two GdBCO bulks with a distance of 12 mm were (100/100) and (110/110), respectively. The trapped field of the GdBCO superconductor bulks exhibited two peaks. The maximum peaks of superconductor bulk S_A (100/100) were 0.30 T and 0.23 T, and the maximum peaks of superconductor bulk S_B (110/110) were 0.35 T and 0.29 T. The critical transition temperature remained between 94 K and 96 K, with superior superconducting properties. The maximum J_{C, self-field} of S_A appeared in specimen b5, which was 4.5 × 10⁴ A/cm². Compared with S_A, the J_C value of S_B had obvious advantages in a low magnetic field, medium magnetic field and high magnetic field. The maximum J_{C, self-field} value appeared in specimen b2, which was 4.65 × 10⁴ A/cm². At the same time, it showed an obvious second peak effect, which was attributed to Gd/Ba substitution. Liquid phase source Y123 increased the concentration of the Gd solute dissolved from Gd211 particles, reduced the size of Gd211 particles and optimized J_C. For S_A and S_B under the joint action of the buffer and the Y123 liquid source, except for the contribution of Gd211 particles to be the magnetic flux pinning center with the improvement of J_C, the pores also played a positive role in improving the local J_C. More residual melts and impurity phases were observed in S_A than in S_B, which had a negative impact on the superconducting properties. Thus, S_B exhibited a better trapped field and J_C.

Keywords: GdBCO superconductor bulk; buffer layer; critical current density; two-seeded technology.