Micro-Raman mapping on an anatase TiO₂ single crystal with a large percentage of reactive (0 0 1) facets

After it has been successfully synthesized in 2008, so far, no Raman investigations on the micro-sized anatase TiO₂ single crystal which has a large percentage of the reactive (0 0 1) facets have been conducted to the best of our knowledge. In the present work, this unique anatase TiO₂ single crystal was investigated by noninvasive and nondestructive Raman mapping technique. Raman images of both non-polarized and polarized measurements showed that the Raman features of the crystal varied with measurement position. The differences among the Raman spectra measured on different crystal facets were believed to result from the orientations and the symmetry rules. Whereas the differences among those measured at different points of the same crystal facet under the same measurement condition were supposed to indicate the defects of the crystal structure, such as oxygen vacancies, local lattice disorder etc. Furthermore, the appearance of the two second order Raman peaks of 803 and 918 cm^-1 as well as the blue-shift of 395 cm^-1 peak implies the anharmonicity of the crystal structure, which is also probably caused by the crystal defects. Our results provide useful information about the structure of this unique anatase TiO₂ material, and could be complementary to those that acquired by other characterization techniques.