The effect of a sintered density (open porosity) of Y 2 BaCuO 5 (Y211) pre-forms on the final porosity and Y211 size within YBa 2 Cu 3 O 7−y (Y-123) products was systematically studied in liquid infiltration growth (LIG) processed Y-123 bulk superconductors with Ag addition. To prepare Y211 pre-forms of various densities, Y211 powder compacts were sintered in air at various temperatures of 900-1200 • C. The single-grain Y-123 bulk superconductors were fabricated by the LIG process with top seeding. It was found that the porosity of the final Y-123 product was fairly dependent on the Y211 pre-form density. When a Y211 pellet of a high density was used as a pre-form for the LIG process, the porosity of the final Y-123 product was greatly reduced. In addition to the reduced porosity, the enhanced Y211 refinement was achieved for the Y-123 product prepared using the dense Y211 pre-form, resulting in the improved critical current density (J c ). The Ag addition was also helpful in eliminating the spherical pores through pore filling with a silver melt. The pore elimination and Y211 refinement mechanism in the LIG-processed Y-123 bulks were explained in terms of the liquid capillary movement and Ag melt and particle coarsening at the (Y211 + melt) state.

Paper ash, a source of C and CaCO3, was used for the first time as a cheap form of submicron particles for doping. 0-10 wt% of the ash was added to Mg + 2B and in situ reacted at 850 •C for 30 min in flowing Ar atmosphere. The CaCO3 decomposed and reacted with B to form CaB6 as an impurity phase. Also, the Tc and the a-axis lattice parameter decreased with increasing ash content, which suggests that C substitution at boron sites occurred. Enhancement of high-field Jc(H), Hirr(T ) and Hc2(T ) was observed with an optimum level of about 5 wt% ash addition

This study presents a new seeding technique, named ‘interior seeding’ which allows the growth of a single REBCO (RE: rare-earth elements) grain in the interior of REBCO compacts. The key techniques of interior seeding are to provide appropriate open space for seeds in the interior of REBCO powder compacts to supply air or oxygen to the seeds, and to minimize the contact area between the seeds and liquid. The advantages of interior seeding are as follows: (1) simultaneous growth from the seed to the top and bottom of the REBCO compacts is possible, (2) fractions of the a-b growth sector and the a-c growth sector on the top surface can be controlled and (3) the top surfaces of the single-grain REBCO bulk superconductors are free from samarium or neodymium contamination from the used seeds. The very large single-grain Y1.5Ba2Cu3O7−y (Y1.5) bulk superconductors (42 mm) were successfully fabricated using a melt growth (MG) process combined with interior seeding. Also, large-grain Y1.5 bulk superconductors (41 mm) with 〈110〉/〈110〉 and 〈100〉/〈100〉 grain junctions were fabricated using multiple interior seeding. In this paper, the detailed process of interior seeding, the development of top surface patterns and the properties of single-grain Y123 bulk superconductors fabricated using interior seeding were reported.

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The microstructural analyses of YBCO bulk single-grain superconductors grown by interior seeding with taller and shorter upper pellets have shown that a suitable upper pellet height can lower the porosity in the upper part of the sample, produce a more appropriate distribution of pinning centres in the form of Y-211 particles and suppress subgrain formation with a higher crystal misalignment in the c-growth sector (c-GS), which can lead to a higher measured trapped magnetic field and a more uniform cone of the trapped-field profile. The observed bulging of the sample surface at the c-GS can be explained by the edge melt distribution model, which shows that macroscopic mass transport to the growth sector occurs with higher growth rates.

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