title: Comment on "Colossal ionic conductivity at interfaces of epitaxial ZrO2:Y2O3/SrTiO3 heterostructures".
abstract: García-Barriocanal et al. (Reports, 1 August 2008, p. 676) reported colossal conductivity enhancements in yttria-stabilized zirconia (YSZ)/strontium titanate (STO) epitaxial heterostructures and claimed that the conductivity was ionic. I argue that the claimed ionic conductivity lacks experimental support and that the observed conductivity enhancement is most probably due to the p-type conductivity of STO.
authors.affiliation: Institut für Festkörperforschung, Forschungszentrum Jülich, 52425 Jülich, Germany. x.guo@fz-juelich.de
authors.forename: Xin
authors.initials: X
authors.lastname: Guo