We developed a simple single-direction melt growth for the fabrication of high-performance REBa2Cu3O y (RE: rare earth element) melt-textured bulks with selective grain growth. In this method, bulks were epitaxially melt-grown from a large plate cut from commercial melt-textured bulks by utilizing the different peritectic temperatures of REBa2Cu3O y . Ag-added YBa2Cu3O y bulks with three crystallographic orientations ([100], [110], and [001]) were successfully prepared. The whole c-grown bulk showed a higher trapped field (∼0.39 T) with more circular distributions than the conventional top-seeded bulk. The proposed method is promising for the fabrication of high-performance melt-textured bulks with high scalability and flexibility.
Since REBCO melt-textured bulks are produced in an extremely carrier underdoped state after melt-growth, oxygen-annealing is required for a few hundred hours to control the oxygen composition throughout the bulks due to their slow oxygen-diffusivity. In this study, we discovered that the oxygen-annealing time can be largely reduced with the introduction of water vapor to the oxygen-annealing process for Ag-added YBCO melt-textured bulks without any degradation of the superconducting properties. It was revealed that highly dense stacking faults were induced to the matrix during this wet oxygen-annealing, which are considered to act as fast diffusion paths of oxygen. The estimated chemical diffusion coefficients of oxygen at 400 °C for the bulk annealed under wet O 2 was ∼4 .3 ×10 −11 m 2 s −1 , which is almost twice as high as that annealed under standard dry O 2 atmosphere. High J c without a decrease in T c was confirmed for the sample annealed under wet O 2 , when the wet O 2 annealing was performed for a moderate time. In addition, a combined oxygen-annealing process, where wet O 2 was supplied for the first 24 h followed by a dry O 2 process for the remaining period, was found to be more effective to achieve both enhanced oxygen-diffusion and maintain high field trapping properties. These improvements are probably because moderate amounts of defects were introduced to the bulk as a function of the duration of the wet O 2 annealing. The introduction of water vapor to the oxygen-annealing process will become a versatile technique to reduce the total processing time of REBCO melt-textured bulks.
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