Development of CoFe2O4 thin films for nitrogen dioxide sensing at moderate operating temperature

• Synthesis of CoFe2O4 thin films by economical spray technique for gas sensing application.
• Structural, morphological and electrical properties of CoFe2O4 thin films.
• Systematic study of gas sensing parameters towards various oxidizing and reducing gases.
• The films show higher gas response to NO2 as compared to other target gases at 150 °C.
• Maximum gas sensor response of 95% to NO2 at 150 °C was observed.

Cobalt ferrite thin films were deposited onto quartz substrates by spray pyrolysis technique and their gas sensing properties were investigated. X-ray diffraction study confirms that films are polycrystalline in nature and exhibit single phase spinel cubic crystal structure. DC electrical resistivity measurement indicates the semiconducting nature of the films. The surface morphology study confirms the formation of grains structure with grain size about 200–400 nm. Room temperature variation of dielectric properties with frequency suggests the normal dielectric performance of the cobalt ferrite thin film. The influence of quantities of spraying solutions on the operating temperature, sensitivity and selectivity, gas concentrations, response and recovery characteristics of gas sensor are systematically tested. The maximum gas response 95% was observed for film prepared at 50 mL quantity of solution for 80 ppm NO2. The films are extremely selective towards NO2 as compared to other target gases. Gas response attains nearly 90% of its initial value after 90 days indicates good durability of the films.

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