Impact of the presence of grain boundaries on the in-plane ionic conductivity of thin film Gd-doped CeO < inf> 2

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Though reports in the literature have been interpreted as indicating that the presence of boundaries between submicron grains has the potential to dramatically increase the ionic conductivity of Gd-doped CeO2 (GDC) films [1-3], unambiguous interpretation is hampered by the lack of a study directly comparing the ionic conductivity of single-crystal GDC films to films that are identical except for the presence of submicron grain boundaries. Techniques are developed to grow GDC films by RF magnetron sputtering from a (10%)Gd2O3-(90%)CeO2 target onto a single crystal r-plane sapphire substrate that, though otherwise are largely identical, differ in that one film is a single crystal while the other is polycrystalline with ∼ 80 nm diameter grains. The ionic conductivity of these films is measured in the temperature range of 400-700 °C in the Van der Pauw geometry. Analysis of the ln(σT) vs. 1/T data reveals the single crystal and polycrystalline GDC thin films differ primarily in that the single crystal film exhibits a lower activation energy for ionic conduction of 0.85 ± 0.01 eV than the 0.99 ± 0.01 eV observed for ionic conduction in the polycrystalline film. The presence of 80 nm grains reduces the ionic conductivity of Gd-doped CeO2 in the temperature range of 400-700 °C. © 2010 Elsevier B.V. All rights reserved.

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Solid State Ionics