Electrical properties of nanometric CGO-thin films prepared by electron-beam physical vapour deposition
Thin-film oxide-ion-conducting electrolytes are of considerable interest for the development of micro-solid oxide fuel cells (μ-SOFCs). In this study, nanocrystalline CGO thin films (with thickness ranging from 0.3 to 1.35 μm) were deposited from a Ce0.9Gd0.1O2−δ target by electron-beam physical vapour deposition onto a selection of substrates (Si, glass, fused silica and Al2O3) which were either maintained at room temperature or at 700 °C during deposition. Films have a columnar microstructure with (111) texture in the surface plane. The crystallinity of the films deposited at a substrate temperature of 700 °C was found to be much superior to those deposited at RT and subsequently heated. Impedance spectroscopy revealed that the in-plane resistivity of the films in air at 900 °C is greater than that of bulk CGO by around two orders of magnitude, with this difference increasing with decreasing temperature. The poor electrical properties of the nanocrystalline films may be considerably affected by the expected higher concentration of strains in comparison with the micrometric sample. The composition of the thin films was also affected by a de-doping process. The in-plane charge transport in films is limited by grain boundaries, mainly due to both a greater grain-boundary volume and higher specific grain-boundary resistivity. Conductivity measurements as a function of oxygen partial pressure reveal a considerably narrower electrolytic domain for the thin films than that of bulk CGO.