Top-seeded infiltration growth process (TSIG) is one of the most important methods for the fabrication of single domain REBCO bulk superconductors, the performance of the samples are mainly closely related with quality of the solid phase pellets. In this paper, we report a new way on how to optimize the solid phase pellets and the properties of the single domain REBCO bulks, including sintering of the solid phase pellets (Y2O3 + BaCuO2), infiltrating of the (Ba-Cu-O) liquid phase and the melting growth process. A group of single domain YBCO bulk superconductors with a diameter of 20 mm have been fabricated by the modified RE +011 TSIG method. Both of the levitation force and trapped field of the samples are increasing first and then decreasing with the increasing of sintering times. The largest levitation force 42.8 N and trapped field 0.41 T (77 K, 0.5 T) is obtained in the sample which was sintered at 1000 ℃ for 4.5 hours, which is mainly related with the optimal microstructure of the pre-sintered solid phase pellets and the YBCO bulk. The results indicate that pre-sintering and high temperature infiltration is a very important method to control the microstructure and improve the physical properties of single domain YBCO bulk superconductors.
The trapped field properties of a single domain GdBCO bulk superconductor with a diameter of 32 mm after being magnetized with different permanent magnets under a field cooling state at 77 K have been investigated. The results show that the maximum trapped field of the sample (B mtr ) is nearly saturated when the diameter of the permanent magnet d20 mm, but the trapped magnetic flux of the sample (Φ s ) is nearly saturated when d30 mm. This indicates that the largest trapped magnetic flux can be obtained when the size of the permanent magnet is close to that of the sample, and it is not necessary to use a more permanent magnet. In addition, a new and unusual phenomenon is found in that Φ s is greater than the magnetic flux of the permanent magnet (Φ PM ) when the diameter ratio between the permanent magnet and the sample is less than a certain value, such as 0.63 in this experiment. The relationship between Φ s and Φ PM was well expressed asThese results can provide a new method to design and control the trapped field properties of a single domain REBCO bulk superconductor during practical applications.
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