Structural and spectral properties of SnO₂ nanocrystal prepared by microemulsion technique

Abstract

Extrafine SnO₂ nanocrystals as small as 2.4 nm were synthesized by the microemulsion method. The grain sizes and crystallization process were measured and investigated by X-ray diffraction. Two growth processes were proposed, and the activation energies of 4.3 and 23 KJ/mol were obtained for respective low-and fast-growth processes. TEM micrographs and the selected-area diffraction recorded their morphology and crystallization, well crystallized at about 773 K. All the IR modes measured by FT-IR spectrometer were assigned. The 616 cm^-1 mode after annealing at 673 K showed fine crystallization. The temperature dependence of the Raman spectra shows that increase in intensity and decrease in linewidth of the 636 cm^-1 mode with the increasing grain size indicate a phonon confinement effect. A new 330 cm^-1 Raman mode originally inactive in bulk, was observed in the SnO₂ nanocrystal by size effect. A low frequency mode at 76 cm^-1 shifts to 38 cm^-1 as the temperature goes up 873 K, which can be characterized to determine the SnO₂ grain sizes.