Analysis of the aging characteristics of SnO2 gas sensors

Two types of tin oxide (SnO2) gas sensors were synthesized, which consist of spherical SnO2 nanoparticles and SnO2 nanorods mixed at different ratio, and their aging processes were studied. Using the Complex Impedance Spectroscopy method the electrical properties that are related to the microscopic structure of the samples were investigated. The evolution of absorption current was measured to analyze the ionic conductance that reflects the charging states of the samples. The results indicate that devices of optimal long-term stability can be obtained by sintering the mixture of SnO2 nanorods and spherical nanoparticles (1:1 weight ratio) at 850 °C. In the samples’ impedance data considerable fluctuation could be seen during the early stage of the aging process, which gradually disappeared after several days. The aging process, which is revealed by the changes in both grain-boundary resistance and capacitance, indicates the corresponding changes in the grain-boundary barrier height and the width of depletion layer. We suggest the DC-field-induced migration of ions within the grain boundaries as the probable cause of the phenomenon.