Abstract
Chemiresistive oxide-based gas sensors came a long way from the first experimental study in 1962 to an important technology making modern world go around. However, the story of gas sensors is far from ending as increasing demand from wireless sensing networks stimulates the development of smart detectors for monitoring all types of gases. While the progress made by trial and error optimization is slowing down, it becomes evident that the technology needs more fundamental understanding of the mechanisms behind the chemiresistive response. Motivated by this, the focus of this thesis was set on identifying the gas sensing reactions in three prototypical systems: (a) SnO2 for sensing reactive gases; (b) inorganic ABO3 perovskites for detecting chemically inert CO2; and (c) soda-lime glass for sensing a broad spectrum of gases. As the materials with distinct properties were chosen for the study, it was not surprising to find out that they exhibit remarkably different sensing mechanisms. First, by using first-principles methods, the chemiresistive effect in SnO2 was proven to occur due to the formation of O2- ions at its (100) facets, which answered a long-standing question on the nature of oxygen ionosorption species in oxides. Second, the CO2 sensing response in ABO3 perovskites was rationalized by ab initio approach revealing band gap modulation effect upon CO2 chemisorption on (001) surfaces of six different perovskite systems. Third, the conventional soda-lime glass was shown to exhibit noticeable gas sensing features, which emerge as a combination of space-charge polarization and reversible formation of surface phases at the glass surfaces. The developed undestending of the mechanisms is expected to guide rational design of novel sensing oxides, and thus, facilitate the advancement of the next generation of gas sensing devices.