Electrical behavior of cerium dioxide films exposed to different gases atmospheres

Abstract

Here we present an easy-reproducible microwave-assisted hydrothermal route for preparing pure nanocrystalline CeO 2 films. The produced materials were characterized using a wide range of techniques (X-ray diffraction, field emission gun scanning electron microscopy, Raman spectroscopy) to understand the synthesis dependent changes in crystallographic structure, and crystallite size. Raman and X-ray diffraction techniques revealed that the films were free of secondary phases and that they crystallize in the cubic structure. The observed hydrodynamic particle size larger than the crystallite size confirms the aggregation phenomenon. Gas sensing measurements have been carried out to rationalize the type and number of surface adsorbed groups and overall nanostructure.Electrical conductance variations, owing to gases adsorption onto semiconductor oxide films surfaces, were observed in this work. Chemiresistive CeO 2 film properties depend on the intergranular barrier heights and width.

Novel gas sensor with dual response under CO(g) exposure: Optical and electrical stimuli

“…From this process, the density of carriers decreases and, as a consequence, the sample resistance increases. In previous work we have proposed that at temperatures high enough (greater than ∼ 200°C) the adsorbed oxygen onto the surface (charged oxygen species such O À ) can diffuse into the grains, annihilating oxygen vacancies and thus reducing the donor concentration [27]. Conversely, if oxygen diffuses out of the grains, vacancies are formed.…”

“…The average crystallite size calculated by Scherrer method was 4.20 nm. The insertion of lanthanum leads to a redistribution of charge density, which can be associated with its greater radial stabilizing effect of oxygen vacancies [27]. The inset depicts the [CeO 8 ] clusters being modified by the insertion of lanthanum, which substitutes the cerium ions generating lattice distortions.…”

“…In previous work, our group worked on the preparation of CeO 2 films coming from nanostructures obtained by the microwavehydrothermal methods and its gas sensing measurements have been carried out to rationalize the type and number of surface adsorbed groups and overall nanostructure. Variations of electrical conductance, as a consequence of gases adsorption onto semiconductor oxide film surfaces, were observed [27]. In polycrystalline materials, it is widely accepted that barriers formed between particles or grains have a Schottky-type nature and that they govern the electrical behaviour.…”

Nanostructured CeO2 Thin Films Prepared by the Sol-Gel Dip-Coating Method with Anomalous Behavior of Crystallite Size and Bandgap

“…Figure 9 shows the Raman spectra of the CeO 2 films Journal of Nanomaterials annealed at different temperatures. The Raman spectra of the samples exhibit a Raman mode at 461 cm -1 which has F 2g symmetry assigned to the cubic structure of the fluorite and can be viewed as a first-order symmetric stretching mode of the Ce-O 8 vibrational units [35]. This mode should be very sensitive to any disorder in the oxygen sublattice resulting from thermal, doping, or crystal size [36], as can be observed on how the FWHM of the F 2g mode increases as the CS decreases in Figure 9.…”

Experimental and ab Initio Studies of Deep-Bulk Traps in Doped Rare-Earth Oxide Thick Films

“…Most resistors have a negative VCR 39 , which implies that at high voltages, the resistance decreases during the pulse. However, a reduction in the electrical conductivity is observed for both vacuum and air atmospheres in the entire range along with a structural expansion after lanthanum addition 23 . This indicates that our samples present a positive resistance coefficient, with a remarkable dependence for the pure CeO 2 film, increasing its resistance for the high-voltage regime.…”