Vortex Pinning Properties of a Single-Grain GdBCO Bulk Prepared From a Spark Plasma Sintered Precursor

Single-grain RE-Ba-Cu-O (REBCO) bulks are tesla-class superconducting magnets known to capture magnetic fields of over 10 T by field-cooled magnetization. However, electromagnetic forces often cause mechanical fractures during and after the magnetization process. As pores in the REBCO bulk act as a starting point for fractures, reducing the porosity of the REBCO bulk is critical. Single-grain GdBCO bulks were fabricated from precursors via a top-seeded melt growth method. The precursors were manufactured using spark plasma sintering (SPS) from GdBa $_{2}$ Cu $_{3}$ O $_{7-x}$ and Gd $_{2}$ BaCuO $_{5}$ powders in a 7:3 molar ratio. For comparison, a conventional precursor was prepared using only uniaxial pressure. The density of the GdBCO bulk increased with that of the SPSed precursor. An SPS temperature of 900 °C produced the densest precursor and GdBCO bulk, respectively, at approximately 93 and 94% of the ideal density of the mixed GdBa $_{2}$ Cu $_{3}$ O $_{7-x}$ and Gd $_{2}$ BaCuO $_{5}$ powders. At 77 K, the trapped magnetic flux density $B_\mathrm{T}$ in SPSed bulks was comparable to that in conventional bulks, but the critical current density was higher. Using an SPS-processed precursor might enhance the vortex pinning properties of single-grain REBCO bulks. To improve the $B_\mathrm{T}$ a GdBCO bulk with a highly homogeneous texture must be prepared by optimizing the fabrication conditions.