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We have fabricated melt-textured Ho-Ba-Cu-O bulk superconductors with a composition of HoBa2Cu3Oy(Ho123)+0.4Ho2BaCuO5(Ho211) in air. Several kinds of precursor compounds having Ho211 starting powders with different sizes are prepared by calcinining Ho2O3, BaO2 and CuO at 1173∼1273 K. The diameter of Ho211 secondary particles dispersed in the Ho123 phase is reduced with decreasing the particle size of the Ho211 starting powder, resulting in the improvement in Jc properties. The maximum Jc value is 7.2×108 A/m2 at 77 K in self-field. The Ag added large single-domain bulk of 32 mm in diameter is also fabricated. The trapped-field of 1.2 T has been achieved at 77 K for this bulk sample.

The effect of Nd422 content on the trapped field was studied for Nd–Ba–Cu–O superconductors. In this system, there are two dominant pinning centers of Nd422/Nd123 interfaces and chemical fluctuation in the matrix. In the present experiment, the average diameter of Nd422 was larger than 2 μm and thus excess Nd422 deteriorated both J c – B properties and crystal growth. However, cracking was introduced in large grain samples with small Nd422 content, which could be prevented by increasing Ag 2 O content from 10 to 20 wt.%. The highest trapped field of 1.4 T was achieved in the sample with a molar ratio of Nd123:Nd422=10:1.5 with 20 wt.% Ag 2 O at 77 K. Furthermore, the secondary peak effect was observed in the field dependence of the trapped field, showing that the field induced pinning is active in large grain samples.