Recently, it has been demonstrated that nanostructured materials increase the transport properties of oxides used as electrolytes in solid oxide fuel cells (SOFC) [1-2]. However, the physical basis of this phenomenon it is not fully understood yet [3,4]. In thin films, electrical properties depend on the technique used and the growth conditions. In this work, nanostructured ceria thin films have been prepared by ultrasonic spray pyrolysis using cerium acetylacetonate as metallo-organic precursor dissolved in anhydrous methanol. The influence of flow rate and substrate temperature in the structural, optical and electrical properties of films was studied. The morphology, structure, optical and electrical properties were studied using scanning electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and impedance spectroscopy (IS). The influence of thermal annealing at 900 ºC on the structural properties of films was studied. The substrate temperature were optimized for obtaining smooth, dense, uniform and homogeneous nanocrystalline films with grains sizes smaller than 20 nm. The flow rate modified the morphology and the grain size of prepared films. By XPS were demonstrated the presence of Ce³⁺, even in treated films. The Ce³⁺ concentration do not depend on the grown temperature. The different signals observed in PL after the thermal annealing are associated to the presence of defects induced by levels in the band gap created by the Ce³⁺ atoms. The low values of total conductivity and activation energy measured by IS are related to the nanometric grain size.

The authors acknowledge financial support for this work from IPN with projects 20181399 and 20181907; CONACyT under project PN 1373 and “Red Temática de Almacenamiento”; and SECITI 095-2017.

References

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