Fabrication and characterization of melt-processed YBCO Page: 3 of 5
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Fabrication and Characterization of Melt-Processed YBCO
S. Sengupta, J. Corpus, and J. R. Gaines, Jr.
Superconductive Components, Columbus, Ohio
V. R. Todt, X. F. Zhang and D. J. Miller
Materials Science Division and Science and Technology Center for Superconductivity, Argonne National Laboratory, Argonne, Illinois
C. Varanasi and P. J. McGinn
Department of Chemical Engineering, University of Notre Dame, Indiana
Abstract - Large domain YBCO are fabricated by using a
melt processing technique for magnetic levitation applications.
A Nda+.Ba2.Cu3Oy seed is used to initiate grain growth and to
control the orientation of YBCO grains. Samples as large as 2
inch have been fabricated by utilizing this method.
Microstructural studies reveals two distinct regions in these
levitators due to different growth mechanism along a/b and c
axis. Some initial result on the mass production of these
levitators are also reported.
The stable levitation or suspension of a magnet is a fascinating
property of a superconductor. A magnet can be levitated above or
suspended below a superconductor and vice versa. A large number
of applications are envisioned using this unique property. These
applications include rotary motion bearings, cryo-coolers, cryo-
flowmeters, energy storage devices, contact less transportation, and
vibration isolators .
For a given magnet and for superconductors with similar
dimensions, the levitation force depends on the critical current
density, J , and the length scale of the induced current loop, d in the
superconductor. The melt processing technique offers an attractive
way to fabricate YBa2Cu30, (YBCO) that can strongly levitate a
magnet -. In a typical melt processing method, YBCO is
heated above its peritectic point where it melts incongruently into
Y2BaCuOs and a Ba- and Cu-rich liquid. The semi-solid melt is
cooled slowly to obtain aligned grains of YBCO or domains. In
order to achieve high levitation forces, large domain size which
determines the d , and high J. is desirable. One way to increase the
domain size is by initiating grain growth by using a seed crystal. In
presence of a favorable temperature gradient the seed not only
ensures a single nucleation site but also permits controlled
orientation of the grains. Using the seeding technique along with a
controlled temperature gradient YBCO domains as large as that of
the sample size (single domain) can be fabricated.
Manuscript received August 27, 1996.
The work at Argonne National Laboratory is partially supported by the US
Department of Energy, Divisiorr of Basic Energy Science-Materials Sciences,
Conservation and Renewable Energy Utility Concepts-Superconductivity
Technology program, under Contract # W-31-109-ENG-38 and by
NSF(DMR91-20000) through Science and Technology Center for
Superconductivity. The work at University of Notre Dame is supported by
DOE Grant DE-FG02-90-ER45427 through Midwest Superconductivity
Fig. 1. Photograph of a large domain YBCO levitator with a diameter of 2
inch. The edge of the sample was coated with a thin layer of Yb2O3 in order to
minimize nucleation from the edges.
Seeding with a single crystal of MgO, A1203, SmBa2Cu30X and
Ndi+xBa2-xCu30y have been reported by various groups -. The
seed can be added to the coldest point of the sample prior to
heating or after an extra melting step. The addition of the seed
prior to heating is preferable as it reduces the difficulty of mass
production. The critical current density, J , is generally controlled
by introducing defects like Y2BaCuOs inclusions and structural
defects like dislocations, stacking faults etc. during melt
In this paper, some of the our recent progress in fabricating
large domain levitators is reported. We also report the
development of microstructure and some of our initial results on
the feasibility of large scale manufacturing of these samples.
II. EXPERIMENTAL METHOD
Phase pure YBa2Cu30x and Y2BaCuOs powders were prepared
by using a low pressure calcination method. Typically, in a low
pressure calcination process, the required oxides and carbonates are
mixed and ball milled in a proper molar ratio. The resulting
powders are then calcined in a low pressure furnace to produce the
desired phase. An oxygen atmosphere with pressure of 2-5 torr is
used during calcination. A partial vacuum is used to increase the
efficiency of removal of CO2. Once the reaction is completed, the
vacuum is discontinued and the powders are cooled in an oxygen
atmosphere at ambient pressure to fully oxygenate the
superconducting powders. The low pressure calcination method is
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Sengupta, S.; Corpus, J.; Gaines, J. R., Jr.; Todt, V. R.; Zhang, X. F.; Miller, D. J. et al. Fabrication and characterization of melt-processed YBCO, report, November 1996; Indiana. (digital.library.unt.edu/ark:/67531/metadc679139/m1/3/: accessed October 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.