An investigation was made of the atomic and electronic structures of interstitial hydrogen impurity in rutile TiO2 and anatase TiO2 using first-principles pseudopotential calculations. The interstitial H atom was attached to the non-bonding p-orbital of an oxygen atom, forming a hydroxyl ion. In rutile TiO2, it was located between two oxygens on an ab-plane. In anatase TiO2, the O-H direction was located along a cubic a-direction. The H was found to be electrically positively charged, and the H impurity level was located above the conduction band minimum, indicating that Hint was a shallow donor-like impurity. Its contamination was expected to lead to n-type conductivity.

Microscopic Properties of Interstitial Hydrogen Impurity in TiO2. Park, D.J., Nahm, H.H., Park, C.H.: Journal of the Korean Physical Society, 2006, 49[2], S473-6