Grain size effects in Bi4Ti3O12 nanocrystals investigated by Raman spectroscopy

The grain size effects in Bi4Ti3O12 nanocrystals were investigated by Raman spectroscopy. The Bi4Ti3O12 nanocrystals with grain size of 48 nm underwent an orthorhombic-to-monoclinic transition at low temperatures. The tetragonal structure of Bi4Ti3O12 nanocrystals with grain size of 23 nm gradually transformed to orthorhombic structure, and then to monoclinic structure with decreasing temperature. However, the tetragonal structure of Bi4Ti3O12 nanocrystals with grain size of 16 nm existed stably in the temperature range 298–77 K. These results showed that the crystal structure and phase transitions in Bi4Ti3O12 nanocrystals were strongly dependent on the grain size.