Annealing temperature effect on structural properties of tin oxide nanoparticles

Tin oxide (SnO2) nanoparticles were synthesized employing simple sol–gel method. Modification in the structural, morphological and optical properties of the as-synthesized tin oxide nanoparticles due to various solution pH (6–12) and thermal annealing at 400 °C (Experiment 1) was studied. X-ray diffraction results of the tin oxide nanoparticles prepared from the precursor solution pH 8 and annealed at 400 °C showed the formation of tin oxide tetragonal phase (SnO2-t) and the surface morphology of the SnO2-t nano- particles studied by scanning electron microscope revealed the formation of spherical shaped agglomerations. Hence, the tin oxide nanoparticles prepared from the solution pH 8 were annealed at 200, 400, 600 and 800 °C in order to study the effect of annealing at various temperatures on the structural, morphological, optical and vibrational properties of tin oxide nanoparticles (Experiment 2). When the annealing temperature was increased to 600 and 800 °C, mixed phases of SnO2-t and tin oxide orthorhombic system (SnO-o) were formed. Various solution pH and annealing temperatures influenced the direct band gap value. SnO2-t phase synthesized from the solution pH 8 and annealed at 400 °C showed a direct band gap of ~4.50 eV. The tin oxide samples annealed at various temperatures showed a slight shift in the fluorescence peak observed at ~327 nm. Raman studies of the samples obtained from Experiment 1 and Experiment   2 showed a slight shift in the vibrational frequency. I–V studies carried out to investigate the electrical properties of the SnO2 thin film formed by simple drop casting method revealed better ohmic contact and its suitability for gas sens- ing applications.