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Published on: December 5, 2015
Microstructural effects on electrical conductivity relaxation in nanoscale ceria thin films
Masaru Tsuchiya1, Nestor A Bojarczuk, Supratik Guha
1Harvard School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.
The Journal of Chemical Physics
|May 12, 2009
Summary
Highly textured ceria thin films exhibit slower oxygen exchange kinetics compared to polycrystalline films, suggesting near-surface defects control oxygen incorporation in nanostructured oxides for fuel cell applications.
Area of Science:
- Materials Science
- Solid State Chemistry
- Nanotechnology
Background:
- Ceria (CeO2) thin films are crucial for solid-state ionic devices like fuel cells.
- Understanding microstructure and electrical conductivity is key to optimizing ceria performance.
- Nanostructured ceria offers potential for enhanced catalytic activity.
Purpose of the Study:
- To investigate microstructure evolution and electrical conductivity relaxation kinetics in highly textured and nanocrystalline ceria thin films.
- To compare the oxygen exchange rates between different ceria film microstructures.
- To elucidate the role of near-surface defects in oxygen incorporation kinetics.
Main Methods:
- Thin film deposition using molecular beam synthesis (MBS) for highly textured films and electron beam evaporation for polycrystalline films.
- High-temperature annealing to study microstructure evolution and grain growth.
- Electrical conductivity relaxation measurements under varying oxygen partial pressures.
- Temperature-dependent experiments to determine activation energies.
Main Results:
- Highly textured ceria films grown by MBS showed no significant structural changes upon annealing.
- Polycrystalline ceria films (10 nm grains) grew to 30 nm upon annealing at 1173 K, with self-limiting grain growth.
- Oxygen exchange rate was significantly slower in highly textured films (0.65 s response time) compared to polycrystalline films (0.13 s response time) at 1148 K.
- Similar activation energies suggested comparable rate-limiting mechanisms.
Conclusions:
- Near-surface defects play a critical role in controlling oxygen incorporation kinetics in nanostructured ceria oxides.
- Microstructure significantly impacts the electrical conductivity relaxation and oxygen exchange rates.
- Findings are relevant for designing efficient catalytic surfaces in solid-state ionic devices, including fuel cells.
