ABSTRACT
So far, the zirconia-based gas sensors have been developed using trial-and-error techniques rather than following an insightful scientific approach. Many of the existing technologies utilize complex mixtures of several different materials, yet the functionality of each component is not known or well understood. Moreover, the degradation mechanisms leading to the aging behavior of zirconia sensors, which was explained in Chapter 1, are not fully understood in most cases. Fundamental knowledge and understanding of the sensing mechanisms are imperative for further development of existing and new composite materials for the SE and RE. There are several factors that determine the feasibility of a sensor technology, such as the magnitude of sensitivity to the measured gas concentration, the response rate, and the cost of the final product. A fundamental understanding of the characteristics of the materials is also important in selecting the appropriate combination of sensing elements to achieve selectivity in complex sensor array structures. Therefore, essential sensor performance parameters (e.g., stability, sensitivity, and selectivity) need to be improved, even in commercially available products. These parameters depend largely on the physical and chemical characteristics of the materials used to build the sensing devices. The specifications for sensing systems are also becoming more demanding (e.g., operation of sensors at higher temperatures or harsh environments, or lower detection thresholds for measuring pollutants).
