Gas sensing properties and modeling of YCoO3 based perovskite materials.

YCoO3 perovskite powder was prepared by the classical sol-gel method, which was extended to the preparation also of non stoichiometric materials or samples containing platinum or palladium, incorporated either during synthesis or a posteriori through impregnation. The prepared powders were characterized in terms of composition and structure, using X-ray diffraction (XRD) and Rietveld refinement. The compounds show a tunnel structure with octahedral framework. The surface properties of these powders were investigated studying their catalytic activity in CO oxidation, as well as their adsorptive features towards oxygen and their redox behavior by means of TPD and TPR respectively. Sensing films of the prepared powders were realized by a screen-printing technique. The electrical properties and response to various gases were studied and found to be correlated to composition and structure of the different materials. Moreover the influence of the mictrostructure was analyzed and a model was developed. The responses to both oxidizing and reducing gases such as CO, NO2, NO, and CH4 were evaluated and discussed both in an inert environment (nitrogen) and in the presence of oxygen (air). All the YCoO3 based sensors show p-type semiconducting properties in the tested environments within the temperature range of 100-380 °C. All the studied materials respond to CO in the high temperature range with a limited response but a large response speed. The response to NOx is optimum in the low temperature range between 160 °C and 200 °C; moreover even at these temperatures both the response and the recovery time are satisfactory. The response towards CH4 results much lower. Finally, the gas sensor properties of the proposed materials proved to be insensitive to ambient humidity.