Vibrational dynamics of anatase TiO2: Polarized Raman spectroscopy and ab initio calculations

Vibrational properties of anatase titanium dioxide single crystal are thoroughly investigated by means both of experimental and theoretical approaches. Polarized Raman-scattering experiments were carried out at room temperature in backscattering geometry on a microcrystalline anatase sample under different crystal orientations set by a micromanipulator. All the independent components of the polarizability tensor were separately obtained. In particular, it was possible to evidence, in turn, the different components of the A(1g) mode, thus unambiguously determining its peak wave number, and then, definitively resolve and identify the A(1g) and B-1g modes of anatase. Moreover, ab initio calculations based on density-functional perturbation theory within the generalized gradient approximation have been performed to evaluate infrared (IR) and Raman modes, dielectric tensors, Born effective charges and TO-LO splitting of the IR modes. The agreement between computational and experimental results is much better than the one achieved in previous computational works.