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Colossal Ionic Conductivity in Epitaxial ZrO2:Y2O3 /SrTiO3 Heterostructures

J. Garcia-Barriocanal,1 A. Rivera-Calzada,1 M. Varela,2 Z. Sefrioui,1 E. Iborra,3 C. Leon,1 S. J. Pennycook,2 J. Santamaria1

Science 321, 676 (2008)

Strained layer superlattices comprising thin films of Y2O3-stabilized ZrO2 (YSZ) between SrTiO3 (STO) spacers show up to eight orders of magnitude enhanced O ion conductivity near room temperature, creating intense interest for their potential to achieve high efficiency fuel cells at low operating temperatures. The conductivity was found to scale with the number of interfaces. The contribution of electronic conductivity through the STO was found to be three to four orders of magnitude lower, demonstrating the ionic nature of the conductivity.

Both X-ray and STEM analysis of the strained thin layers showed them to be highly coherent with the YSZ lattice rotated 45??q to that of the STO. EELS showed no detectable change in the Ti fine structure, indicating that a Ti 4+ configuration is predominant at the interface plane, which is consistent with the lack of electronic conductivity. However, changes were seen to the O fine structure, indicating a change in coordination. This would be expected since the O sublattices of YSZ and STO are different and incompatible across the interface, and may give rise to an enhanced number of oxygen vacancies (shown shaded in the model structure) and structural disorder. The interfacial ionic conductivity could therefore exhibit liquid-like diffusivities, explaining the colossal ionic conductivity of the superlattice.

Z-contrast image of the superlattice obtained in the VG Microscopes HB603U microscope showing the YSZ layer (yellow arrow) coherently strained to the STO. The inset is a low magnification image obtained in the VG Microscopes HB501UX. White arrows show the growth direction

1GFMC, Universidad Complutense de Madrid, Madrid 28040, Spain
2Materials Science & Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
3Escuela Técnica Superior de Ingenieros de Telecomunicaciones. Universidad Politécnica de Madrid. Madrid 28040, Spain.


 Oak Ridge National Laboratory