Structure and Vibrational Dynamics of NASICON-Type LiTi2(PO4)3

Small single crystals of NASICON-type LiTi2(PO4)3 of high quality were grown by means of long-term annealing of polycrystalline specimens synthesized using conventional solid state reaction. A thorough study of their structural properties and vibrational dynamics was carried out by means of an integrated experimental and theoretical approach. A single-crystal X-ray diffraction analysis at room temperature allowed us to determine the precise crystal structure and the anisotropic displacement parameters of all atoms. In addition, all the 25 independent components of the polarizability tensor, expected on the basis of the group theory for the LiTi2(PO4)3 crystal, were observed using polarized Raman spectroscopy in backscattering geometry on a microcrystal, properly oriented by a micromanipulator. Thus, all the expected Raman modes have been unambiguously identified by determining both their wavenumber and symmetry throughout an accurate analysis of the spectral profiles observed in the different polarization configurations. Finally, these experimental findings were fully corroborated by the results of first-principles calculations performed to determine Raman and infrared vibrational modes.