Investigations into the structure of PEO-layers for understanding of layer formation

•Crystalline TiO2 structures of anatase and rutile into the PEO-treated surfaces.•Increasing crystallinity from bottom to the top of the PEO-layer.•Different average crystallite sizes on top and the bottom of the oxide layer.•Small crystals visible at the bottom and in the titanium substrate.•Amorphous TiO2 around the resulting PEO-pores due to molted and evaporated TiO2.