| Résumé | Films of Fe-doped SrTiO3 deposited using pulsed laser deposition on sapphire and alumina, when exposed to propane, showed different sensor responses measured sas a resistance changed as a function of temperature and microstructure. The film deposited on alumina has a stronger response towards 3000-ppm propane than does the film deposited on sapphire. Films deposited on alumina exhibit higher dc conductivity than the films on sapphire. The activation energies indicate a mixed electronic/ionic conduction at low temperature with the high-temperature regime showing a temperature-independent conductivity. The origin of the difference in gas responses caused by varying temperature and morphology has been explored using ac impedance techniques and measured as a function of frequency s1 Hzøfø1 MHzd and temperature s200øTø480 °Cd. A single relaxation sa single semicircle in the complex impedance planed in the frequency domain was observed in addition to the relaxation due to the electrode-film interface. A model and a mechanism of conduction for the above are derived using equivalent circuits to fit the ac impedance data and dc conductivity. It is proposed that the reduction of Fe-doped SrTiO3, which is induced by propane, enhances the space-charge barrier near the grain boundaries and increases the sensitivity to propane. |
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