Current–voltage characteristics and selective CO detection of Zn2SnO4 and ZnO/Zn2SnO4, SnO2/Zn2SnO4 layered-type sensors

The current–voltage characteristics and the CO gas-sensing properties of porous Zn2SnO4 were examined. ZnO/Zn2SnO4 and SnO2/Zn2SnO4 layered-type samples were also fabricated for the investigation of the interfacial effect between ZnO (or SnO2) and Zn2SnO4 by sequentially die-pressing respective powders. To form a stable contact between ZnO (or SnO2) and Zn2SnO4, the composition and thus the sinterability of ZnO (or SnO2) was controlled. The electrical and gas-sensing properties of the layered samples were compared with those of individual ZnO, SnO2 and Zn2SnO4. Zn2SnO4 showed the higher sensitivity values to CO gas than to H2 gas at relatively low temperature. The sensitivity of Zn2SnO4 decreased with the increasing magnitude of applied voltage at high temperature. Both SnO2/Zn2SnO4 and ZnO/Zn2SnO4 layered-type samples showed the sensing characteristics varying with the direction of applied bias. The interface between Pt and Zn2SnO4 was responsible for the observed non-ohmic current–voltage characteristics and the resultant gas sensitivity.