Phase transformation analysis of the phosphate containing and carbon doped titania nanotubes, prepared by a simple anodization method, reveals complete transformation from amorphous to anatase phase in air between 360 and 400 degrees C. Activation energies for formation of anatase phase are evaluated and compared for the two types of titania nanotubes. A detailed analysis of the phase transformation characteristics and stability of the anatase phase is reported. (C) 2008 Elsevier Ltd. All rights reserved.