The Influence of Y-211 Content on the Growth Rate and Y-211 Distribution in Y–Ba–Cu–O Single Grains Fabricated by Top Seeded Melt Growth

Abstract

The melt processing of Y–Ba–Cu−O (YBCO) single grains has been investigated using different isothermal temperature profiles for precursor powders containing varying amounts of Y-211. The crystal morphology of the as-grown YBCO single grains and the growth rate, which is influenced critically by the initial Y-211 content and the under-cooling temperature, have been analyzed. A simple method to determine an optimum temperature profile for the growth of bulk YBCO single grains has been proposed based on the results of this investigation. The influence of the initial Y-211 content on the macrosegregation of Y-211 inclusions for the different crystallographic orientations and different under-cooling temperatures has been analyzed. The correlation between the initial Y-211 content and the macrosegregation of Y-211 inclusions within the YBCO single grain along the different growth directions is interpreted from the growth rate data using Y-diffusion mechanism and pushing/trapping theory. Finally, an improved method for fabricating bulk YBCO superconductors containing a uniform distribution of pinning centers in the single grain, which has significant potential for improving the superconducting properties of bulk YBCO superconductors for practical applications, is proposed.

The use of buffer pellets to pseudo hot seed (RE)–Ba–Cu–O–(Ag) single grain bulk superconductors

“…that immediately beneath the seed) in the sample grown without a buffer layer is the lowest of all the positions. This is expected since the Y-211 particles react with the liquid phase to form the Y-123 phase more extensively under conditions of low under-cooling [27]. It should be noted that this Y-211 concentration is also lower than that at position 1a in the samples fabricated with a buffer layer.…”

“…In other words, when a buffer layer is used, the concentration of Y-211 in the sample will be higher at a position close to the seed because the 1a position in the sample fabricated with a buffer layer is more distant from the seed. This sample would therefore contain more Y-211 particles at positions more distant from the seed due to the associated higher growth rate [27] according to the results from image analysis, and according to trapping/pushing phenomenon [28]. Of course, the distribution of the Y-211 phase can also be affected by other factors, such as precursor powder composition, heating profile and the temperature distribution within the furnace.…”

Improving Mechanical Strength of YBCO Bulk Superconductors by Addition of Ag

“…INGLE grain (RE)Ba2Cu3O7 [(RE)BCO] bulk high temperature superconductors (HTS), where RE=Y, Gd or Sm, are able to trap significantly larger magnetic fields than those generated by conventional permanent magnets [1], [2]. This enables a wide range of potential practical applications for these materials, including Maglev trains, energy storage systems and trapped flux devices [3]- [5].…”

Corrosion of YBCO bulk superconductor in air

“…Bulk single‐grain superconductors based on YBa 2 Cu 3 O 7‐δ (further Y123, YBCO or 123) compounds are highly attractive materials for practical applications, therefore they are intensively studied . One of the important problems affecting the application of these superconductors is the tendency to irreversible degradation due to exposure to ambient atmospheric conditions .…”