Polarized Raman, FTIR, and DFT study of Na2Ti3O7 microcrystals

Sodium trititanate Na2Ti3O7 microcrystals were carefully prepared by sodium carbonate and titanium dioxide solid-state reaction and characterized by scanning and transmission electron microscopies, selected area electron diffraction, X-ray powder diffraction, and Raman and Fourier transform infrared spectroscopies. Electron microscopic techniques revealed that the samples were formed by elongated particles several microns long with broad size distributions. The zone axis and crystal growth direction of the elongated particles were determined by selected area electron diffraction. These results were useful for identifying the symmetries of the optical vibrational modes obtained by infrared absorption and polarized Raman scattering of oriented crystals. For a complete assignment of the depicted phonon modes, Fourier transform infrared spectroscopy and Raman data were compared with theoretical data obtained from first-principles calculations within the framework of the density functional theory. A very nice agreement was established between the characteristic features of measured and calculated vibrational modes. In particular, all optical phonon modes of Na2Ti3O7 could be experimentally observed and assigned to their correct symmetries. These results must be useful for describing the physical behavior of the system and designing new technological applications.