Evaluation of oxygen adsorption based on the electric properties of SnO₂ semiconductor gas sensors

We successfully prepared SnO₂ nanoparticles of two different sizes by hydrothermal synthesis and calcination at 400°C to evaluate the oxygen adsorption equilibrium constant K_(O2-ad) on a particle surface. The K_(O2-ad) values were calculated from the relationship between the electric resistance and the oxygen partial pressure (P_O2). The K_(O2-ad) values of 7 and 17 nm SnO₂ nanoparticles were almost in the same range when the donor densities of these nanoparticles are the same. Additionally, the sensor responses of these nanoparticles to hydrogen were affected by the surface-area-to-volume ratio because the K_(O2-ad) values are the same. Thus, we propose that the K_(O2-ad) value can be evaluated on the basis of the relationship between the electric resistance and P_O2.