Effects of Hydrothermal temperature on the physical properties and anomalous band gap behavior of ultrafine SnO2 nanoparticles

Abstract

In the present study, tin oxide nanostructures were synthesized using hydrothermal method, without surfactant and/or template, and the impact of the hydrothermal temperature of synthesis on the physical properties of the samples was evaluated. Rietveld analysis of X-ray diffraction patterns was used to measure the nanocrystallite size of the samples, which was estimated at 7.1–18.5 nm. In addition, the morphology of the samples was evaluated by the FESEM analysis and nanosphere morphology was observed. Moreover, the band gap of the samples, that were synthesized at lower temperatures, was approximately 3.46 eV, which was smaller compared to the band gap of the bulk tin oxide. On the other hand, the gap of the samples synthesized at higher temperatures was equal to the bulk band gap of this material. This means a band gap shrinkage was observed in ultrafine SnO2 nanoparticles. The variations of lattice vibrations with the synthesis temperature were indicated by the Raman spectroscopy and the correlation of the presence and intensity of new vibrational modes with the size of the nanocrystallites were studied.