Boundary effects on the electrical conductivity of pure and doped cerium oxide thin films

Abstract

Thin films of CeO(2) (both nominally pure and 10 mol% gadolinium-doped) grown via pulsed-laser deposition were studied. The electrical conductivity of the samples was measured as a function of thickness, temperature and oxygen partial pressure (pO(2)) using impedance spectroscopy. As expected, undoped CeO(2) exhibits electronic conductivity (with activation energy between 1.4 and 1.6 eV) whereas the highly doped samples are oxygen vacancy conductors (activation energy around 0.7 eV for epitaxial films). In order to investigate the influence of the nature of the substrate the thin films were grown on two different substrates, Al(2)O(3) (0001) and SiO(2) (0001), and compared. While the films grown on SiO(2) exhibit a microstructure characterized by columnar grains, the films grown on Al(2)O(3) are epitaxial. Notably, for films on both substrates the conductivity and activation energy vary with film thickness and exhibit remarkable differences when the films on different substrates are compared. In the case of the polycrystalline films (SiO(2) substrate), the space charge layer effects of the grain boundaries dominate over the substrate-film interface effect. In the case of the epitaxial films (Al(2)O(3) substrate), a small interface effect, probably due to a space charge layer or structural strain, is observed.

Tensile Lattice Distortion Does Not Affect Oxygen Transport in Yttria-Stabilized Zirconia–CeO2 Heterointerfaces

“…The MgO substrate with a 10 nm thick STO buffer layer was initially characterized. The resulting conductivity of the STO layer was about 10 -4 S cm -1 at 700° C. At the same temperature, CeO 2 epitaxial films showed a conductivity more than one order of magnitude larger, 18 in turn more than two orders of magnitude smaller than the bulk conductivity of 9.5YSZ. 19 As discussed previously thin oxide films grown by PLD at high temperature and in relatively low oxygen partial pressure are typically partially reduced.…”

“…where c bg * is the background 18 O concentration (measured at 0.0022) and c g * is the 18 O concentration of the annealing gas (0.258). The profiles obtained for each layer type were fitted to this equation using a regression analysis fit in Matlab.…”

“…Fig. 8 also reports the conductivities YSZ and CeO2 used to calculate , and the conductivity of single 15 crystal 9.5YSZ from reference [18]. The conductivity of sample D calculated using the diffusion coefficient measured by SIMS is also reported for comparison in the same figure.…”

“…This material is available free of charge via the Internet at http://pubs.acs.org. The sample is gold coated with a region masked off, as shown schematically in (a), the sample is exposed to an 18 O enriched atmosphere allowing 16 O- 18 O exchange solely at the trench edge. The gold capping layer is then removed allowing SIMS analysis (b) resulting in a 3-dimensional dataset (c), which can be separated into layer types.…”

Cerium reduction at the interface between ceria and yttria-stabilised zirconia and implications for interfacial oxygen non-stoichiometry

“…[7][8][9][10][11] Previous investigations suggested different possible explanations of the interfacial effects such as misfit dislocations, segregations of dopants, strain, and space charge regions. 12,13 However, possible mechanisms for the enhanced ionic conductivity in CeO 2 /YSZ hetero-structures are still under discussion. Since interface atomic structures and chemistry are deemed to play crucial roles, it is key to microscopically investigate defined CeO 2 /YSZ interfaces, in order to be able to improve the transport properties of these hetero-structured systems.…”