Assessment of the Cr doping and size effects on the Raman-active modes of rutile TiO2 by UV/Visible polarized Raman spectroscopy

The Raman signal is highly sensitive to lattice distortions, doping, size effects or excitation source, among other factors. The coexistence of these effects makes occasionally difficult the interpretation of variations in Raman spectra. In this work, size and Cr doping effects have been evaluated by the study of Raman spectra of different undoped and Cr-doped rutile TiO2 samples. In the Raman study, two laser sources have been employed with wavelengths in the visible (633nm) and UV (325nm) respectively, which entail different surface and spectral sensitivities. Polarization effects have been also evaluated, by modifying the orientation of the probed microstructures with respect to the laser polarization. It has been found that Cr incorporation increases vibration modes at 110, 154, 700 and 810cm(-1), some of them showing strong dependence with the laser polarization. The relation of these vibration modes with a possible doping-induced activation of the Raman-inactive B-1u and A(2u) modes, as well as the influence of size effects on the Raman spectra, is evaluated and discussed. Copyright (c) 2017 John Wiley & Sons, Ltd.