Transparent TiO2 films were produced via sol-gel spin and dip-coating techniques. Soda-lime glass (SLG) and SiO2 precoated glass were used as substrates. The thin films were characterized by X-ray diffraction (XRD), X-ray reflectometry (XRR), optical profilometer and glow discharge optical emission spectroscopy (GD-OES). Na migration was detected in the amorphous TiO2 films which are deposited on SLG substrates. In order to prevent sodium migration a barrier layer was introduced between TiO2 film and glass. The beneficial role of this barrier layer on alkali migration is verified and the mechanism of prevention of migration is proposed relying on the results of GD-OES depth pro. le measurements. (C) 2008 Elsevier B. V. All rights reserved.