A low-fluorine solution with a 2:1 F/Ba mole ratio for the fabrication of YBCO films: Paper

Publication: Research - peer-reviewJournal article – Annual report year: 2014

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In previously reported low-fluorine MOD-YBCO studies, the lowest F/Ba mole ratio of the precursor solution was 4.5. Further lowering the F/Ba ratio would bring benefits for the environment, thick film deposition, and an understanding of the heat treatment process. On the other hand, the F/Ba ratio must be at least 2 for full conversion of the Ba-precursor to BaF2 to avoid the formation of BaCO3, which is detrimental to the superconducting performance of YBCO films. In this study, a solution with a 2:1 F/Ba mole ratio was developed, and the fluorine content of this solution was approximately only 10.3% of that used in the conventional TFA-MOD method. Attenuated total reflectance-Fourier transform-infrared spectra (ATR-FT-IR) revealed that BaCO3 was remarkably suppressed in the as-pyrolyzed film—and eliminated at 700 °C. Thus, YBCO films with a critical current density (Jc) of over 5 MA cm−2 (77 K, 0 T, 200 nm thickness) could be obtained on lanthanum aluminate single-crystal substrates. In situ FT-IR spectra showed that no obvious fluorinated gaseous by-products were detected in the pyrolysis step, which indicated that all F atoms might remain in the film as fluorides. X-ray diffraction θ/2θ scans showed the presence of BaF2—but not of Y F3 or CuF2—in films quenched at 400–800 °C. The formation priority of BaF2 over Y F3 and CuF2 was interpreted by examining the chemical equilibrium of the potential reactions. Our study could enlarge the synthesis window of precursor solutions for MOD-YBCO fabrication, and serve as a foundation for continuously and systematically studying the influence of fluorine content in the precursor solutions.
Original languageEnglish
Article number055006
JournalSuperconductor Science & Technology
Volume27
Issue number5
Number of pages10
ISSN0953-2048
DOIs
StatePublished - 2014
CitationsWeb of Science® Times Cited: 12

    Keywords

  • YBCO film, Low-fluorine, F=Ba ratio, Phase evolution, Chemical equilibrium
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