Microstructural change of nano-SnO2grain assemblages with the annealing temperature

The microstructural changes of nano-${\mathrm{SnO}}_2$ have been systematically studied using x-ray diffraction and Raman spectroscopy. The nano-${\mathrm{SnO}}_2$ grain assemblage possesses some features of the rutile structure, but has a large amount of defects: vacancies of oxygen, vacancy clusters, and local lattice disorder at the interface and interior surface, which lead to a significant lattice distortion and an evident space-symmetry reduction of ${\mathrm{D}}_{4\mathrm{h}}^{14}$ and the appearance of a group of new Raman peaks. Two major Raman peaks ${\mathrm{N}}_1$ and ${\mathrm{N}}_2$ in accordance with Matossi's force constant model have been found. When the annealing temperature is close to 673 K, the density of vacant lattice sites and local lattice disorders decreased rapidly in the grains, and the lattice distortion and Raman peaks ${\mathrm{N}}_1$ and ${\mathrm{N}}_2$ almost disappeared at the same time. It suggests that ${\mathrm{N}}_1$ and ${\mathrm{N}}_2$ are closely related to the microstructural change of the nanocluster grains, or in other words, ${\mathrm{N}}_1$ and ${\mathrm{N}}_2$ peaks mark an additional characteristic of space symmetry of the grain assemblage of nano-${\mathrm{SnO}}_2$. The Raman peak ${\mathrm{N}}_3$ may be related to local ${\mathrm{SnO}}_2$ clusters and vacancy clusters.