SnO$_2$–ZnO nanocomposite is synthesized at room temperature using the successive ionic layer adsorption and reaction (SILAR) method. The X-ray diffraction (XRD) patterns of annealed films confirms the formation of SnO$_2$–ZnO nanocomposite. Scanning electron microscopy depicts the porous agglomerated nanoparticle network-like structure of the SnO$_2$–ZnO nanocomposite. On the other hand, ZnO has a cauliflower shape, while SnO$_2$ has a distributed agglomerated nanoparticle-like morphology. Energy dispersive X-ray spectroscopy (EDS) confirms the elemental compositions of composite films. The reducing gases such as liquefied petroleum gas, ethanol, hydrogen sulphide and ammonia weredetected using a SnO$_2$–ZnO nanocomposite sensor. Ethanol has a maximum sensitivity of 56.93% at a temperature of 275°C and a concentration of 24 ppm. In addition, as compared to a bare sensor, a composite sensor responds quickly. The n–n heterojunction at intergrain boundaries is responsible for better composite performance over bare sensors. Even at low gas concentrations, the SnO$_2$–ZnO nanocomposite sensor is found selective towards ethanol.

Perovskite GdAlO$_3$ oxides were prepared by a simple and convenient solution combustion method. In synthesis, nitrates of gadolinium and aluminium were used as a precursor and that of urea and glycine was used as a specific fuel for the synthesis of GdAlO$_3$. Nitrates of Gd, Al and urea were taken in proper stoichiometric proportion to synthesize A1, A2 and A3. The obtained GdAlO$_3$ powder was sintered at 850°C temperature. The X-ray diffractometer patterns of samples confirm the formation of polycrystalline GdAlO$_3$ with an orthorhombic structure. The Williamson– Hall plot analysis confirms that the average particle size varies between 20 and 30 nm. The Fourier transform infrared spectral analysis confirms that the synthesized powder itself is phase pure. The field-emission scanning electron microscopy and transmission electron microscopy study reveals porous lump development over the substrate. The elemental composition of the samples was confirmed by energy-dispersive X-ray spectroscopy analysis. The bandgap energy of GdAlO$_3$ was varied between the ranges 3.80 to 3.90 eV. The gas sensing performance of GdAlO$_3$ was systematically examined for LPG, NO$_2$, NH$_3$ and H$_2$S for different operating temperatures and for various concentrations. The GdAlO$_3$ exhibits maximum sensitivity of 20.04% towards 100 ppm of LPG at temperature of 225°C.