Polarization-Dependent Raman Spectroscopy of Anatase and Rutile TiO2 Microcrystals

Phase transition from anatase to rutile is critical in the photocatalysis of TiO2. Few Raman studies have been done on the anatase micro-sized TiO2 single crystals with a high percentage of the (001) reactive facet. Direct observation of phase transition from anatase to rutile would enable the synergistic effect between anatase and rutile in photocatalysis. Here, single micro-crystals were investigated by polarized Raman microscopy to understand the phase transition of anatase TiO2, particularly the transformation of crystalline structure. The Raman mappings and spectral intensities of the micro-crystalline structures were compared with the spectral intensities of nature mineral single crystalline structures and those expected from analytical calculations. Experimental polarized Raman spectra showed that the A1g and B1g peak intensities of both rutile and anatase micro-crystals agree with those of nature single crystal. Further, the Raman mappings showed that the ratio of the combined A1g and B1g peak intensity to the Eg peak intensity at facet boundaries is dependent upon polarization state. The difference in intensity at the (101) facets was most likely the result of stress or Raman scattering geometry.