Ionic Conductivity Increased by Two Orders of Magnitude in Micrometer-Thick Vertical Yttria-Stabilized ZrO₂ Nanocomposite Films

Abstract

We design and create a unique cell geometry of templated micrometer-thick epitaxial nanocomposite films which contain ∼20 nm diameter yttria-stabilized ZrO₂ (YSZ) nanocolumns, strain coupled to a SrTiO₃ matrix. The ionic conductivity of these nanocolumns is enhanced by over 2 orders of magnitude compared to plain YSZ films. Concomitant with the higher ionic conduction is the finding that the YSZ nanocolumns in the films have much higher crystallinity and orientation, compared to plain YSZ films. Hence, “oxygen migration highways” are formed in the desired <i>out-of-plane</i> direction. This improved structure is shown to originate from the epitaxial coupling of the YSZ nanocolumns to the SrTiO₃ film matrix and from nucleation of the YSZ nanocolumns on an intermediate nanocomposite base layer of highly aligned Sm-doped CeO₂ nanocolumns within the SrTiO₃ matrix. This intermediate layer reduces the lattice mismatch between the YSZ nanocolumns and the substrate. Vertical ionic conduction values as high as 10^–2 Ω^–1 cm^–1 were demonstrated at 360 °C (300 °C lower than plain YSZ films), showing the strong practical potential of these nanostructured films for use in much lower operation temperature ionic devices