Gas-sensing properties of nanostructured CeO2-xZrO2 thin films obtained by the sol-gel method

With the use of sol-gel technology and heat-treatment at a temperature of 500°, we obtained CeO₂-xZrO₂ (where = 0, 5, 10, 20, 30, 50 mol%) powders and thin films that are promising for oxygen detection. A phase composition of the samples was studied using XRD and Raman spectroscopy. It was shown that under these synthesis conditions, both for powders and films, an increase in the content of zirconium dioxide from 0 to 50 mol% entailed the formation of solid solutions with a fluorite crystal lattice in the structure of cerium dioxide. For CeO₂-xZrO₂ thin films (where = 0÷30 mol%), gas-sensing properties were studied: we identified a resistive response to oxygen in a wide range of concentrations (0.4–20%) at a low operating temperature of 400 °C, and studied the effect of moisture on the signal obtained while detecting O₂. Upon increase of humidity from 0 to 100% resistance and response to oxygen values decrease, and from 75% and larger humidity a significant worsening of kinetic properties occurs, such as response time and recovery time. Selectivity to analyte gases such as H₂, CO, CH₄, NO₂ was studied. The best selectivity to oxygen was displayed by the film containing 20% ZrO₂, while the film with 10% ZrO₂ demonstrated the worst selectivity. Using Raman spectroscopy it was shown that, after studies in a gas-air mixture containing not more than 1% of reducing gases, the nanomaterial surface contained oxygen superoxides and peroxides that were not removed, even after subsequent heat treatment in air at 500 °C.