Colossal Ionic Conductivity at Interfaces of Epitaxial ZrO ₂ :Y ₂ O ₃ /SrTiO ₃ Heterostructures

Abstract

The search for electrolyte materials with high oxygen conductivities is a key step toward reducing the operation temperature of fuel cells, which is currently above 700 degrees C. We report a high lateral ionic conductivity, showing up to eight orders of magnitude enhancement near room temperature, in yttria-stabilized zirconia (YSZ)/strontium titanate epitaxial heterostructures. The enhancement of the conductivity is observed, along with a YSZ layer thickness-independent conductance, showing that it is an interface process. We propose that the atomic reconstruction at the interface between highly dissimilar structures (such as fluorite and perovskite) provides both a large number of carriers and a high-mobility plane, yielding colossal values of the ionic conductivity.

Tensile Lattice Distortion Does Not Affect Oxygen Transport in Yttria-Stabilized Zirconia–CeO2 Heterointerfaces

“…6,9 However, STO is not a good insulator at high temperatures, and conductivity measurements of thin films deposited on STO might be significantly affected by the substrate. 11 (100) and (110) MgO substrates, for which the insulating properties at high temperatures are well demonstrated, have been used for the fabrication of grain-boundary-free ultra-thin 8.7 mol% yttriastabilized zirconia (8.7YSZ 1 ) layers.…”

Chemical Bonding and Atomic Structure in Y2O3:ZrO2‐SrTiO3 Layered Heterostructures

“…[3] YSZ is a commonly used electrolyte in solid oxide fuel cells (SOFCs) run at high temperatures (> 800 8C), and such an increase in ionic conductivity at lower temperatures would be expected to have a substantial impact on the performance of SOFCs. [4] However, considerable discussion has followed the original publication, with the suggestion that the increased conductivity may be partly electronic in origin.…”

“…[3] It is difficult to probe the structure of interfaces within thin films experimentally, and previous attempts for YSZ-STO films seem inconsistent. The relative orientation of the YSZ and STO regions has been determined by X-ray diffraction [10] and scanning transmission electron microscopy, [3,8] with YSZ rotated by 458 about the [001] axis relative to STO. However, electron energy loss spectroscopy suggests that the STO is terminated with a TiO 2 layer [3] in layered YSZ-STO, whereas experimental attempts to grow YSZ on STO substrates with different terminations show that [001]-oriented YSZ can only be reliably grown epitaxially on SrOterminated STO, [10] leaving the preferred termination of the STO in question.…”

“…[1] For example, a conducting two-dimensional electron gas was discovered at the interface between the two insulators LaAlO 3 and SrTiO 3 . [2] The atomic arrangements within heterostructures of complex functional oxides determine the resulting properties and are not necessarily straightforward to construct based on the bulk crystal structures of the independent components.…”

“…García-Barriocanal et al reported that an epitaxial heterostructure of nanometer-sized layers of Y 2 O 3 -stabilized ZrO 2 (YSZ) and [001]-oriented SrTiO 3 (STO) has an up to eight orders of magnitude higher conductivity than bulk YSZ at room temperature. [3] YSZ is a commonly used electrolyte in solid oxide fuel cells (SOFCs) run at high temperatures (> 800 8C), and such an increase in ionic conductivity at lower temperatures would be expected to have a substantial impact on the performance of SOFCs.…”