Single domain Y?Ba?Cu?O (YBCO) composed of a YBa2Cu3Oy (Y-123) superconducting bulk matrix with discrete, non-superconducting Y2BaCuO5 (Y-211) phase inclusions has been fabricated by a seeded infiltration and growth (IG) technique in the form of cylindrical pellets up to 32?mm in diameter. Sample shrinkage in the radial direction for single domains prepared by this technique is relatively low at 5% and independent of sample size, in contrast to the shrinkage observed in samples grown by conventional melt processing, which increases significantly with increasing sample diameter. Furthermore, samples grown by the IG technique exhibit low porosity of typically 0.9% of the bulk volume fraction, compared with a corresponding value of around 4.9% observed in samples fabricated by conventional melt processing. Fine Y-211 particles were observed to be embedded within the Y-123 superconducting matrix for the IG processed samples, leading to a high critical current density, Jc, of over 100?000?A?cm?2 at 77.3?K in self-field. The distribution of Y-211 particles in the IG sample microstructure, however, was inhomogeneous (unlike in previous reports), which leads to a variation in the spatial distribution of Jc. The volume fraction of Y-211 in the vicinity of the seed crystal (i.e.?corresponding to the initial c-sector growth stage), in particular, is typically around 5%, compared with a value of up to 30% in the a growth sectors more distant from the seed crystal (which corresponds well to the theoretical value for the sample composition studied here). The volume fraction of Y-211 inclusions in the c growth sector more distant from the seed was around 22%. Finally, a trend of the variation in the distribution of Y-211 particles in the Y-123 matrix grown by the IG technique was similar to that in sample grown by conventional melt processing.

https://iopscience.iop.org/article/10.1088/0953-2048/18/11/002/pdf

Seeded infiltration and growth of large, single domain Y–Ba–Cu–O bulk superconductors with very high critical current densities

Large, single-grain Y–Ba–Cu–O (YBCO) was fabricated via the infiltration of Ba–Cu–O liquid into a precursor body composed of solid, porous Y2BaCuO5 (Y-211) and observed to trap a magnetic field of 0.15 T at 77 K. In this process a NdBCO seed crystal was used to promote heterogeneous nucleation, which allows the fabrication of single-grain YBCO containing a uniform and very fine distribution of Y-211 inclusions in the YBa2Cu3O7−δ(Y-123) matrix without the addition of Pt. These superior microstructural features and significant field trapping ability compared with samples processed by conventional top-seeded melt growth suggest this technique could be a practical alternative for processing large, single-grain superconductors for engineering applications.

Fabrication of Large Single-grain Y–Ba–Cu–O Through Infiltration and Seeded Growth Processing

An infiltration and top seed growth method (ITSG), has been successfully used to grow a single grain of YBa2Cu3O7−x (Y123) bulk material. The nucleation of Y123 grain is controlled by seeding the Y2BaCuO5 (Y211) preform with a Sm123 or MgO seed crystal. Various configurations influencing the liquid infiltration such as that due to capillarity or gravitational force have been studied. The resulting mono-domain Y123 samples are found to be free of macrocracks, a negligible shrinkage and a microstructure with uniformly distributed fine Y211 particles. The superconducting properties of the final Y123/Y211 samples are discussed.

http://iopscience.iop.org/article/10.1088/0953-2048/17/11/014/pdf

Infiltration and top seeded grown mono-domain YBa2Cu3O7−x bulk superconductor

Buffer-aided top seeded infiltration and growth (TSIG) with a suitable liquid phase reservoir has been compared with the top seeded melt growth (TSMG) process and applied successfully to fabricate single grain YBa2Cu3O7-δ​(YBCO) bulk superconductors. A Yb-based liquid phase has been observed to yield the homogeneous, high density YBCO single grains by the TSIG technique. Sintering the Y2BaCuO5(Y-211) preform prior to TSIG has been found to be critical in retaining the shape of the sample during the infiltration and growth process. A number of advantages of the TSIG process have been demonstrated, including a dramatic reduction in sample shrinkage and a general improvement in bulk microstructure. TSIG processed samples also exhibit a fine and even distribution of unreacted, embedded Y-211 inclusions that play a key role in flux pinning in the fully processed bulk material. A YBCO sample of diameter 25 mm fabricated by the optimised buffer-aided TSIG process was able to trap a field of 0.63 T at 77 K, which is the highest value of trapped field ever reported for a YBCO sample fabricated by the TSIG process. The technique reported here has the potential to improve further the microstructural and superconducting properties of single grain bulk YBCO, which enhances further the applications potential of these materials.

https://www.repository.cam.ac.uk/bitstream/1810/251235/3/Kumar%20et%20al.%202015%20Journal%20of%20the%20European%20Ceramic%20Society.pdf

An improved top seeded infiltration growth method for the fabrication of Y–Ba–Cu–O bulk superconductors

Large, single-grains of (LRE)-Ba–Cu–O (LRE=light rare earth: Nd, Sm, and Gd) bulk high-temperature superconductors with significantly improved properties have been fabricated in an air atmosphere using a practical processing technique based on seeded infiltration growth. This process involves the use of a generic seed crystal, developed recently at the IRC in Superconductivity, to promote epitaxial grain nucleation. The formation of a solid-solution phase within the nucleated single grain is then suppressed effectively by providing excess Ba to the growth front under an air processing atmosphere. Critical current densities in excess of 105A∕cm2 at 77K have been observed in the resulting large grain samples, with an associated and significant improvement in trapped magnetic field. This air-based seeded-infiltration-growth process offers a significant degree of freedom both in terms of the processing parameters and the reproducibility in growth of oriented single grains.

Fabrication of high performance light rare earth based single-grain superconductors in air

NdBa 2 Cu 3 O 7-δ (Nd-123) superconductor has been processed to obtain a highly textured microstructure with micrometer-sized spherical Nd 4 Ba 2 Cu 2 O 10 (Nd-422) inclusions through a process that involves the infiltration of liquid phases into a shaped preform followed by its slow cooling through the peritectic formation temperature of Nd-123. The process was carried out in high-purity argon (maximum of 4 ppm of oxygen) to reduce the formation of low-T c solid solutions. A major advantage of the process is that it minimizes the possibility of Nd-422 coarsening in the liquid. The result is a very uniform distribution of nearly spherical Nd-422 inclusions with 80% of the particles having a diameter less than 1 μm, in the highly textured Nd-123 matrix. Since the present process eliminates shrinkage and large hollows within the interior of the samples, it can enable the fabrication of 3-dimensional complex-shaped objects with good dimensional tolerance and high J c for applications. The critical current densities in the Nd-123/Nd-422 composites have been measured and the values obtained are discussed in the context of the microstructure of the material.

Nadendla Hari Babu

Papers

Infiltration-Growth Processing of NdBa2Cu3O7-delta Superconductor