This paper reports the effect of niobium on the structure of titanium dioxide (TiO2) thin films deposited on glass. The results obtained indicated that the direct current (DC) co-sputtering of Ti and Nb onto glass substrates in the presence of oxygen results in the formation of Nb-doped anatase thin films with strong preferential orientation. In the concentration range between 0 and 40 at.% Nb, niobium is incorporated into the TiO2 lattice according to a substitution mechanism, entering Ti sites in the cation sub-lattice. No evidence exists for a solubility limit < 40 at.% of Nb under the applied deposition conditions, however, it is not believed that an equilibrium situation prevails. Lattice charge compensation was concluded to occur by the formation of cation vacancies for samples with up to 10 at.% Nb, and by Ti3+ or Nb4+ ions for the samples with >= 15 at.% Nb, the latter in conj. unction with cation vacancy compensation. (c) 2006 Elsevier B.V. All rights reserved.