Development of nanocrystalline CrNbO4 based p-type semiconducting gas sensor for LPG, ethanol and ammonia

Nanocrystalline chromium niobate (CrNbO4) was synthesized by a low temperature niobium-citrate complex process. Thermal analysis (TG/DTA), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) with energy dispersive X-ray spectroscopy (EDX), diffuse reflectance spectra (DRS), impedance analysis and Brunauer–Emmett–Teller (BET) surface area measurement were used to characterize the prepared CrNbO4. XRD results indicated that the tetragonal phase of CrNbO4 was obtained after calcined at 800 °C for 2 h. TEM analysis showed an average particle diameter of 25 nm. From the diffuse reflectance spectrum measurement, the band gap was found to be 2.08 eV. The temperature dependent conductivity obeys the Arrhenius relation. The activation energy of the conductivity process was calculated to be 0.41 eV. The BET results indicated that the surface area of CrNbO4 nanopowder was 32.36 m2/g. Finally, the gas sensing behavior of CrNbO4 nanopowder was studied for liquid petroleum gas (LPG), ethanol (C2H5OH) and ammonia (NH3) as a function of various controlling factors like operating temperature, concentration of the gas and response time. It revealed that CrNbO4 is a promising candidate for the detection of LPG (0.87) and ethanol (0.66), when compared with NH3 (0.49).