A series of SnO2-Co3O4 composite thick films (about 10μm thick) containing 0-100% Co3O4 by mass of the composites were prepared from the component oxides through mixing by ball-milling for 24h, screen-printing and sintering at 700°C for 3h. The composite films were found to exhibit n- or p-type response to CO and H 2 depending on the Co3O4 contents of the composites. The n-type response was exhibited at 200°C or above by SnO 2-rich composites (Co3O4 content up to 5mass%). The sensor response to both CO and H2, defined as R a/Rg, where Ra and Rg are electrical resistances in air and gas, respectively, was promoted strongly by the addition of small amounts of Co3O4 to SnO 2, and the response at 250°C as correlated with the Co 3O4 contents went through a sharp maximum at 1mass% Co3O4. The p-type response, obviously originating from Co3O4 (p-type), was exhibited at 200°C or below by the composites containing 25-100mass% Co3O4. Remarkably, sensor response to CO, defined as Rg/Ra, was larger with the 50% Co3O4 composite than with the neat Co 3O4, while the reverse was true for the response to H 2. Thus fairly sensitive and selective detection of CO over H 2 was possible with the 50% Co3O4 composite. The physical state of the composites and the mechanisms of promotion of n- and p-type response were discussed.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Surfaces, Coatings and Films
- Metals and Alloys
- Electrical and Electronic Engineering
- Materials Chemistry