Two-dimensional vacancy trapping in yttria doped ceria

• Yttria doped ceria films were created with nanometer-scale composition modulation.
• Oxygen vacancies accumulated in pure CeO2 layers adjacent to doped regions.
• At the limit, samples were heterogeneously doped using Y2O3/CeO2 multilayers.
• Ion conduction occurred mainly within the space charge regions for these samples.

Thin film processing methods offer a number of means to investigate and engineer ion conduction in solid electrolytes. In this work, we present fabrication and characterization of Y-doped CeO2 thin films where the Y-dopants were distributed homogeneously or were condensed into increasingly concentrated layers, to the limit of alternating layers of pure Y2O3 and pure CeO2. Both the entire film thickness and net Y-concentration were kept constant such that only the spatial distribution of dopants was altered. Space charge regions formed at interfaces between regions with varying vacancy concentrations, yielding vacancies trapped within two-dimensionally arranged accumulation regions. A Gouy–Chapman model was implemented in order to further investigate the distribution of the accumulated oxygen vacancies in the space charge regions of pure CeO2 layers. Comparison of the measured activation energy of conduction indicates that in films with intermediate dopant condensation, conduction occurred predominantly by vacancies trapped in the Y-containing layers. Conversely, in the film composed of alternating layers of Y2O3 and CeO2, vacancies trapped in the CeO2 space charge regions became significantly conductive, thus providing a means to determine the properties of vacancies in ceria that are trapped near dopants.