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The prime objective of the current research was to analyze and utilize the coexistence of basic and acidic metal oxide semiconductors (MOS) for sensing pollutant gases. In the current work, 1 wt.%, 3 wt.%, 5 wt.%, 7 wt.%, and 9 wt.% NiO (basic MOS) was added to MoO3 (acidic MOS), and thick films were prepared using the screen printing technique. Structural characterization was performed by x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive x-ray analysis (EDAX). The crystallite size was about 50 nm, with intermediate voids. EDAX analysis confirmed the non-stoichiometric composition of the films. The films were oxygen-deficient as per EDAX data. An electrical analysis involving resistivity, temperature coefficient of resistance (TCR), and activation energy was also performed. NiO3 samples showed maximum resistivity of 103.13 × 104 Ω·m and minimum activation energy of 0.3953 eV. The electrical analysis predicted the distinct behavior of the NiO3 sample. A negative TCR value indicated the semiconductor-like behavior of the samples. The pollutant gas response of the samples was analyzed using a static gas sensing apparatus. NiO3 samples showed gas sensitivity of 87% towards the ethanol vapors, with good selectivity, as compared with the responses towards CO, liquid petroleum gas (LPG), NH3, and NO2 gases. The oxygen vacancy-based gas sensing mechanism was the probable reason for the improved ethanol vapor sensing. The response time of the sample was 28 s, while the recovery time was 38 s. [ABSTRACT FROM AUTHOR]

The aim of this study is to prepare thick films of MoO3 with various weight percentages of aluminum dopant and study its gas sensing characteristics. The thick films were prepared on alumina substrate using easily reproducible, cost-effective screen printing method. The films were characterized using XRD, FESEM, EDS and static gas sensing apparatus. The XRD analysis confirmed the presence of Molybdenum trioxide (JCPDS 05-0508) and aluminum (JCPDS 31-0026). The XRD conveyed that aluminum has occupied an interstitial position and got oxidized to alumina. FESEM showcased the characteristic lamellar structure of MoO3 with voids. The EDS data showed that films were having oxygen excess and the oxygen vacancies increased with aluminum doping percentage. Resistivity and activation energies decreased first and then increased with dopant (aluminum) percentage. The Al5 films showed a minimum resistivity (6 1. 0 5 × 1 0 4 Ω m) and activation energy (0.19 eV). The TCR had a negative value for all five films supporting n-type semiconductor behavior of the films. The Al5 films showed 84.3% sensitivity to 1000 ppm of NO2 gas at 200°C. Authors discussed adsorption-desorption based gas sensing mechanism in detail. Research work tested efficient NO2 gas sensor using aluminum-doped MoO3 thick films. [ABSTRACT FROM AUTHOR]