Ionic conductivity and activation energy for oxygen ion transport in superlattices—the semicoherent multilayer system YSZ (ZrO2 + 9.5 mol% Y2O3)/Y2O3

Abstract

The oxygen ion conductivity of YSZ (ZrO₂ + 9.5 mol% Y₂O₃)/Y₂O₃ multilayer systems is measured parallel to the interfaces as a function of temperature between 350 and 700 °C. The multilayer samples are prepared by pulsed laser deposition (PLD). The film thicknesses, the crystallinity, the texture and the microstructure are investigated by SEM, XRD, HRTEM and SAED. To separate the interface contribution of the total conductivity from the bulk contribution the thickness of the YSZ and Y₂O₃ layers is varied systematically. The total conductivity of the YSZ films increases when their thickness is decreased from 0.53 μm to 24 nm. It depends linearly on the reciprocal thickness of the individual layers, thus on the number of YSZ/Y₂O₃ interfaces. This behaviour results from the parallel connection between individual conduction paths in the bulk and the interfacial regions. The activation energy for the ionic conductivity decreases from 1.13 to 0.99 kJ mol⁻¹ by decreasing the thicknesses of the individual YSZ layers. HRTEM studies show that the YSZ/Y₂O₃ interfaces are semicoherent. The correlation between interface structure and ionic conduction is discussed.