We report a new process which promises high critical current density in oxide superconductors. The process consists of three stages. Firstly a YBa2Cu3O
x
sample is rapidly heated and quenched from the Y2O3 plus liquid region. Subsequently the quenched sample is reheated to the Y2BaCuO5 plus liquid region, and then slowly cooled with a temperature gradient in flowing oxygen. The process enables us to grow a superconducting phase unidirectionally and to suppress the second phase intrusion, leading to the production of well textured YBa2Cu3O
x
which yields a high J
c value in the presence of magnetic fields. It is also found that Bean's critical state is realized in such high J
c samples.
Trapped magnetic flux density of melt-grown YBaCuO bulk superconductors was evaluated. A single-grained disc-shaped bulk sample with a size of 45 mmφ×15 mm trapped very high magnetic flux density after field cooling. One disc trapped a maximum surface flux density of 0.72 T, while the maximum of double-piled discs was 1.35 T after 100 seconds. A polygrained sample showed a much lower maximum. The pinning potential of this single-grained disc was 0.17 eV, and the overall critical current density estimated from the trapped flux density was about 7×103 A/cm2. Since these values are lower than those of a small-sized sample, weak links are still expected to exist even in the single-grained sample. Domain structure within a grain is a strong candidate for this weak link.
Platinum addition in precursors of melt processing could produce finely dispersed Y2BaCuO5 (211) inclusions of about 1 µm in YBa2Cu3O
x
matrix. This fine dispersion of 211 resembles that of quench-and-melt-grown materials. The platinum-added sample exhibited a critical current density exceeding 2×104A/cm2 at 77 K and 1 T. Platinum is considered to enhance the nucleation of 211 which forms by the pertitectic reaction between Y2O3 and liquid phase.
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