High quality (Sm 0.5 , Eu 0.5 )Ba 2 Cu 3 O 7−δ single domains were grown in air with BaCuO 2−x addition. It was found that a RE-Ba substitution (RE: Sm and Eu) could be effectively suppressed by a small addition of BaCuO 2−x . The 94 K superconductivity with sharp transition was obtained in the composition range of 0.16 ∼ 0.33 BaCuO 2−x and (Sm 0.5 , Eu 0.5 )Ba 2 Cu 3 O 7−δ in a molar ratio. At 77 K, a surface field of 0.8 T was trapped in a single-domain pellet of 3.2 cm diameter. A further addition of BaCuO 2−x deteriorated the microstructure and degraded the superconducting performance.
We investigated the effect of Ag2O addition on the microstructures, the superconducting properties, the field-trapping capabilities and the mechanical properties of Nd–Ba–Cu–O (Nd123:Nd422 = 10:2) bulk superconductors. The samples were added with 10 wt% and 20 wt% Ag2O and grown in 1% O2–Ar atmosphere. The superconducting properties and the field-trapping capabilities were not affected by Ag2O content; however, the mechanical properties were greatly improved with increasing Ag2O content. The sample with 20 wt% Ag2O exhibited the Weibull coefficient exceeding 13.
We used Ba–Cu–O substrates to fabricate bulk Nd–Ba–Cu–O superconductors using a
top-seeded melt-growth method. There were several advantages for the use of
Ba–Cu–O substrate compared to conventional substrate materials such as MgO,
ZrO2,
Al2O3, RE123 and
RE211 (RE = rare earth). The Ba–Cu–O did not react with the precursor and minimized liquid loss.
Accordingly, the introduction of large-sized cracks was suppressed. We also found that
Tc
values were high at the bottom regions, which was ascribed to the beneficial effect of
Ba–Cu–O in suppressing Nd/Ba substitution. As a result, we obtained bulk Nd–Ba–Cu–O
superconductors that exhibited fairly good field-trapping capabilities, even at the bottom
surfaces.
The formation mechanism of fine Gd211 particles was studied by observing the size and morphology of Gd211 in the Gd–Ba–Cu–O melt-quenched from 1100 °C with various Gd211 particle sizes. The size and distribution of Gd211 particles at the partial melting stage depended on the size of initially added Gd211 particles. The precursor with fine Gd211 starting powder formed fine needle-shaped Gd211 particles after melting. The Gd211 refinement is ascribable to the increased number of Gd211 nucleation sites and growth inhibition by Pt addition. We also studied the refinement of RE211 (Nd422) particles in other RE–Ba–Cu–O (RE: Y, Dy, Eu, Sm, Nd) systems. In the cases of Y-, Dy- and Nd-systems, the size of RE211 (Nd422) particles could be reduced by decreasing the size of RE211 (Nd422) starting powders. In contrast, the employment of fine RE211 starting powder was not so effective for the size reduction of RE211 particles in the Eu- and Sm-systems.
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