Enhancement of oxygen ion conductivity in oxides is important for low-temperature (<500 °C) operation of solid oxide fuel cells, sensors and other ionotronic devices. While huge ion conductivity has been demonstrated in planar heterostructure films, there has been considerable debate over the origin of the conductivity enhancement, in part because of the difficulties of probing buried ion transport channels. Here we create a practical geometry for device miniaturization, consisting of highly crystalline micrometre-thick vertical nanocolumns of Sm-doped CeO₂ embedded in supporting matrices of SrTiO₃. The ionic conductivity is higher by one order of magnitude than plain Sm-doped CeO₂ films. By using scanning probe microscopy, we show that the fast ion-conducting channels are not exclusively restricted to the interface but also are localized at the Sm-doped CeO₂ nanopillars. This work offers a pathway to realize spatially localized fast ion transport in oxides of micrometre thickness.

The oxygen pressure effect on the structural and ferroelectric properties have been studied in epitaxial BaTiO₃ (BTO)/SrRuO₃/SrTiO₃ (001) heterostructures grown by pulsed laser deposition. It is found that oxygen pressure is a sensitive parameter, which can influence the characteristics of oxide films in many aspects. The out-of-plane lattice parameter, tetragonality, (c/a) and Ti/Ba ratio monotonously decrease as the oxygen pressure increases from 5 mTorr to 200 mTorr. Microstructural study shows that the growth of BaTiO₃ varies from a dense large grained structure with a smooth surface to a small columnar grain structure with rough surface as the deposition pressure increases. Electrical measurements show that the 40 mTorr deposited BTO films present maximum remanent polarization (P_r) (14 μC/cm²) and saturation polarization (P_s) (27 μC/cm²) due to the stoichiometric cation ratio, very smooth surface, and low leakage current. These results demonstrate that the controlling of cation stoichiometry, surface morphology, and leakage current by oxygen pressure is one of very important prerequisites for device applications in the BaTiO₃ films.