The effect of size, morphology and crystallinity of seed crystals on the nucleation and growth of Y–Ba–Cu–O single-grain superconductors

Abstract

The effect of size, morphology and crystallinity of seed crystals on the nucleation and growth of melt processed Y–Ba–Cu–O (YBCO) during top seeded melt growth (TSMG) has been investigated. Conventional seeding of bulk YBCO with a small seed crystal of square planar or irregular geometry leads to point nucleation of the YBa2Cu3O7−δ (Y-123) phase and a subsequent square planar c-sector growth habit. The use of seeds of triangular and round geometries, however, results in a deviation from this growth habit symmetry. The use of large surface area seed crystals of dimensions 20 mm × 10 mm, on the other hand, influences the growth of bulk YBCO in two significant ways. Firstly, rapid epitaxial nucleation of the Y-123 phase occurs beneath the seed crystal, followed by grain growth via the usual peritectic solidification in the incongruent melt. Secondly, a large area seed reduces the processing time of large single grains compared to that achieved by TSMG with small area seeds. The present study is particularly relevant to the fabrication of single-grain samples with controlled growth sectors, reduced processing times and the multiple seeding of large area bulk materials containing good grain boundaries.

Reliable single grain growth of (RE)BCO bulk superconductors with enhanced superconducting properties

“…These features of the buffer-assisted melt process can be observed clearly in figure 6, and particularly in figure 6(e). The buffer acts effectively as a larger seed [21] during the seeding process, which increases the size of c-growth region, given that the size of epitaxial nucleus for the main bulk single grain is the same as that of the large (buffer) seed [22]. Furthermore, buffers also minimise the effects of 'particle pushing' in the vicinity of seeded area, so that the distribution of RE-211 is relatively uniform across the entire single grain [21].…”

Natural strategies for creating non-equilibrium morphology with self-repairing capability towards rapid growth of excellent YBa2Cu3O7−δ crystals

“…By replacing the normal equilibrium-shaped square seed, unconventional single-seeds with irregular geometry or nonequilibrium sides have been investigated, such as triangular or circular shaped (Sudhakar Reddy et al, 2005), or (110)-sided ones (Qian et al, 2018;Nizhelskiy et al, 2007). In Fig.…”

Peritectic melting of thin films, superheating and applications in growth of REBCO superconductors

“…65, which certainly affect the growth and the performance of REBCO bulk superconductors. In this point of view, the use of large-sized seed (LSS) to induce the growth of large sized crystal with the high volume fractions of c-GS is commonly considered due to its several advantages [148,149]. Firstly, the use of LSS with large-area epitaxial-growth results in fully-growth along the a-axis direction shortly, and prevents the crystal from self-nucleation on the a-b plane surface, which readily occurs during the long period of growing time.…”