Synthesis and characterization of binary and ternary metal oxide nanostructures for gas and humidity sensing applications

Abstract

Measurement of gas and humidity are the very common component for a broad spectrum of industries and technologies. Hence, it is crucial to improve sensors operated under ambient conditions. Chemiresistive sensors exhibit high sensitivity, quick response, good reproducibility with no hysteresis, tough durability, long life, and low cost. Transition-metal oxides demonstrate diverse and complicated bonding properties due to d-orbitals with variable oxidation states. Again, it is easier to generate defects in TMOs in comparison to non-transition metal oxides. Therefore, suboptimal and structural uncertainty factors govern the aptness of some oxides over the others. Although binary metal oxide like ZnO, SnO2, NiO, and Co3O4, etc. have appealed ample consideration in last decades for their distinctive characteristics, still further development of semiconductors are highly desirable and in this theme investigation of ternary oxide semiconductors (II–IV–VI oxides) make them ideal for their use from ambient to extreme working conditions. The avid interest to achieve excellent chemical sensing performance will be very fruitful to study the role of doping, post processing thermal treatment, synthesis of ternary structures, etc. on metal oxides. This thesis broadly describes gas and humidity sensing applications of metal-oxides. The gas sensing study of p-type metal oxides is hitherto lacking and attracts research interest. To apprehend this idea, NH3 gas sensing of ptype NiCo2O4 ternary oxide and a plausible mechanism for anomalous n-type sensing is pronounced. Irrespective of widely acknowledged literature on humidity sensing properties of ZnO, a huge research gap is existent between role of surface and sensing mechanism. A similar type of nonexistence further prevail from the experiment results of ZnO even on doping or construction of ternary forms like ZnSnO3. More interestingly least study was carried out on the correlation between sensitivity and hysteresis in metal oxide based humidity sensors where later one causes measurement error during sensor operation and its possible way of minimization. These scarcity of research in highly potent theoretical and experimental fields worth meticulous investigation of varied aspects to improve sensing performance using metal oxides motivated to opt various metal oxides like ZnO, NiCo2O4, and ZnSnO3.