Modification and Conversion of E-beam
Co-evaporated Precursors for Fabricating
High Critical Current YBa₂Cu₃O_7-δ Films

Yifei Zhang, Ron Feenstra,
Claudia Cantoni, David K. Christen, and Dean J. Miller

Abstract—Ex situ conversion of e-beam co-evaporated precursors was studied in an effort to fabricate high critical current YBCO films using the BaF₂ process. It was shown that an intermediate oxygenation annealing prior to the conversion modifies the precursor crystallinity and promotes c-axis epitaxial growth while randomly-oriented film formation is suppressed. With the modified precursors, a critical current density
(J_c, 77 K & 0 T) of 2.1 MA/cm² measured by SQUID magnetometry was obtained in 1.8 μm thick YBCO films. This corresponds to an estimated transport critical current I_c of about 500 A/cm-width. The mechanism of the pre-annealing effect was investigated by characterization of the precursors, quenched films, and fully converted films using XRD, SEM, and TEM. Cross-sectional TEM was used to study the early nucleation of YBCO film at the precursor/substrate interface. The significant effect of the precursor modification indicated that, in addition to optimizing conversion processing parameters, modifying the precursor is an effective way to achieve the desired epitaxial film structure and to obtain higher critical currents, I_c.

Index Terms—critical current density, epitaxial growth, nucleation, YBCO film.

Manuscript received 25 August 2008.
This work was sponsored by the U.S. Department of Energy, Office of Electricity Delivery and Energy Reliability and Basic Energy Sciences as part of a DOE program to develop electric power technology. The work at Oak Ridge was performed under contract No. DE-AC05-00OR22725 with UT-Batelle, LLC. The work at Argonne was performed under contract W-31-109-ENG-38.
Y. Zhang, R. Feenstra, C. Cantoni, and D. K. Christen are with the Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA (phone: 865-574-6264; fax: 865-574-6263; e-mail: zhangyf@ornl.gov).
D. J. Miller is with the Argonne National Laboratory, Argonne, IL 60439 USA (e-mail: miller@anl.gov).

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