  Multilayered heterostructures of Ce0.85Sm0.15O2-delta and Y0.16Zr0.92O2-delta
of a high crystallographic quality were fabricated on (001) - oriented MgO
single crystal substrates. Keeping the total thickness of the heterostructures
constant, the number of ceria-zirconia bilayers was increased while reducing
the thickness of each layer. At each interface Ce was found primarily in the
reduced, 3+ oxidation state in a layer extending about 2 nm from the interface.
Concurrently, the conductivity decreased as the thickness of the layers was
reduced suggesting a progressive confinement of the charge transport along the
YSZ layers. The comparative analysis of the in-plane electrical
characterization suggests that the contribution to the total electrical
conductivity of these interfacial regions is negligible. For the smallest layer
thickness of 2 nm the doped ceria layers are electrically insulating and the
ionic transport only occurs through the zirconia layers. This is explained in
terms of a reduced mobility of the oxygen vacancies in the highly reduced
ceria.
