Low-Temperature Superionic Conductivity in Strained Yttria-Stabilized Zirconia

We report very high lateral ionic conductivities in epitaxial cubic yttria-stabilized zirconia synthesized on single crystal SrTiO3 and MgO substrates by reactive direct current magnetron sputtering. Superionic conductivities (i.e., ionic conductivities of the order ~1 Ω -1 cm -1 ) are observed at 500 oC for 58-nm-thick films on MgO. Our results indicate a superposition of two parallel contributions – one due to bulk and one attributable to the film-substrate interface. Interfacial effects dominate the conductivity at low temperatures (<350 o C), showing more than three orders of magnitude enhancement compared to bulk YSZ. At higher temperatures, a more bulk-like conductivity is observed. The films have a negligible grain-boundary network, thus ruling out grain boundaries as a pathway for ionic conduction. The observed enhancement in lateral ionic conductivity is caused by a combination of misfit dislocation density and elastic strain in the interface. These very high ionic conductivities in the temperature range 150 – 500 oC are of great fundamental importance but may also be technologically relevant for low-temperature applications.