Structure and chemistry of interfaces between ceria and yttria-stabilized zirconia studied by analytical STEM.

•In the interface a gradual reduction Ce4+→Ce3+ is revealed. The Ce reduction is confined to 6–8 (1 1 1) atomic planes.•Chemical intermixing occurs at the interface forming a ceria/zirconia solid solution also 6–8 atomic planes wide.•Systematic scan deflections are observed in STEM EELS linescans which are explicable by assuming a space charge at the interface (positive on the YSZ side, negative on the Ce oxide).•While the in-plane lattice mismatch of 5.3% is accommodated by misfit dislocations, out-of-plane a quasi-continuous transition from YSZ to CeO2 is facilitated within the intermixing zone in accordance with Vegard´s Law for a quasi-ternary system (CeO2–Ce2O3–YSZ). An excess lattice expansion measured in one single (1 1 1) plane at the interface is explicable by considering oxygen vacancy diffusion from Ce oxide to YSZ, thus providing an explanation for the space charge.