Synthesis and characterization of InNbO4 nanopowder for gas sensors

Indium niobate (InNbO4) nanopowder was prepared by a comparatively low temperature niobium citrate complex process. The prepared InNbO4 was characterized by thermal analysis, X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy, diffuse reflectance spectroscopy (DRS), and impedance studies. It revealed that the well crystalline monoclinic InNbO4 nanopowder was obtained at the calcination temperature of 600 °C. The average particle diameter was 22 nm. The optical band gap was found to be 2.66 eV. The temperature dependent conductivity obeyed Arrhenius relation. The activation energy of the conductivity process was calculated to be 0.43 eV. The gas sensing behaviour of the prepared InNbO4 was studied by measuring the change in resistance of the sensor material as a function of various concentrations of the test gases such as liquid petroleum gas (LPG), ammonia (NH3) and ethanol (C2H5OH) at their optimized operating temperature. InNbO4 had a better sensitivity to LPG (0.97) and NH3 (0.70) gas than ethanol (0.46). The sensor responses of InNbO4 as a function of gas concentrations and with recovery time were also studied in detail.