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Electromagnetic, atomic structure and chemistry changes induced by Ca-doping of low-angle YBa2Cu3O7–δ grain boundaries

Nature Materials volume 4, pages 470–475 (2005)Cite this article

Abstract

Practical high-temperature superconductors must be textured to minimize the reduction of the critical current density Jgb at misoriented grain boundaries. Partial substitution of Ca for Y in YBa2Cu3O7–δ has shown significant improvement in Jgb but the mechanisms are still not well understood. Here we report atomic-scale, structural and analytical electron microscopy combined with transport measurements on 7° [001]-tilt Y0.7Ca0.3Ba2Cu3O7–δ and YBa2Cu3O7–δ grain boundaries, where the dislocation cores are well separated. We show that the enhanced carrier density, higher Jgb and weaker superconductivity depression at the Ca-doped boundary result from a strong, non-monotonic Ca segregation and structural rearrangements on a scale of ∼1 nm near the dislocation cores. We propose a model of the formation of Ca2+ solute atmospheres in the strain and electric fields of the grain boundary and show that Ca doping expands the dislocation cores yet enhances Jgb by improving the screening and local hole concentration.

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Figure 1: Voltage–current characteristics.
Figure 2: GB facet structure from the micrometre to the nanoscale.
Figure 3: Atomic structures of dislocation cores for pure and 0.3Ca-doped [001]-tilt YBCO grain boundaries.
Figure 4: Ca segregation at the GB of the 0.3Ca-doped sample and Ca concentration variations perpendicular to and along the GB plane.
Figure 5: Oxygen EELS spectra measured on the pure and 0.3Ca-doped GBs.
Figure 6: Surface plot of the distribution of Ca2+ solute ions near a periodic chain of edge dislocations in a 7° GB calculated from equation (1).

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Acknowledgements

We are grateful to James Buban and Nigel Browning, formerly of the University of Illinois at Chicago, for experimental help, discussions and for access to the JEOL2010F there. We thank Steve Pennycook from ORNL for discussions. The work was supported by AFOSR under grant F49620-03-01-0429.

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  1. Applied Superconductivity Center, University of Wisconsin, Madison, 53706, Wisconsin, USA

    Xueyan Song, George Daniels, D Matt Feldmann, Alex Gurevich & David Larbalestier

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Correspondence to David Larbalestier.

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Song, X., Daniels, G., Feldmann, D. et al. Electromagnetic, atomic structure and chemistry changes induced by Ca-doping of low-angle YBa2Cu3O7–δ grain boundaries. Nature Mater 4, 470–475 (2005). https://doi.org/10.1038/nmat1394

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