Abstract
Linear sweep voltammetry, photocurrent spectroscopy, impedance and reflectance measurements have been used to study the growth and stability of anodic oxide films on titanium in 
and 
. Films were grown typically to a formation voltage of 40V (∼100 nm) and had a density close to that of anatase, 3.9 g cm−3. Two regimes of oxide film instability have been identified. The first occurs during growth and is manifested by a reduction in growth current efficiency preceded by unusual photocurrent and impedance behavior. The second, which occurs when the field is reduced, appears as a sharp current spike accompanied by film thickening and sudden changes in the impedance and photocurrent conversion efficiency. A link between the two phenomena is established and the dependence on growth rate and formation voltage discussed. A model based on the formation of a damaged surface layer covering a fresh barrier layer is presented.