Heterogeneous TiO2 films with nanocrystalline (nc-) rutile and amorphous (a-) phases were annealed in vacuum up to 450 degrees C. The structural and morphological changes were studied by in situ X-ray absorption and ex-situ X-ray diffraction and atomic force microscopy. The annealing process leads to phase and morphological changes depending on the initial phase mixture. Films with dominant nc-rutile phase are quite stable whereas in a-TiO2-containing films the a-TiO2 regions crystallize into nc-anatase at 300 degrees C. The latter is attributed to the initial anatase-like character of a-TiO2. Interestingly, at 450 degrees C nc-anatase or nc-rutile is preferentially promoted for high or low initial a-TiO2 contents, respectively. (C) 2011 Elsevier B.V. All rights reserved.