The nature of defects in reduced pure and Nb‐doped TiO2 rutile is investigated at high temperature by Seebeck coefficient measurements. The classical point defect model approach allows a good fit of the theoretical curves to experimental data. In undoped rutile, the main defects should be titanium interstitials in a large oxygen partial pressure range. For small departures from stoichiometry, the influence of impurities and band to band thermal excitation is discussed. In the case of Nb‐doped rutile, two kinds of compensation may occur. Some conclusions related to transport phenomena in such materials are drawn.

The electrical conductivity of rutile doped with 0.04–3 at.% niobium is reported as a function of oxygen pressure in the temperature range 1273–1623 K. The charge compensation is discussed in terms of a point defect model, under the assumption of a substitutional incorporation of niobium into the titanium rutile sublattice. Two kinds of charge compensation occur according to the temperature and the oxygen pressure, via an electronic or a lattice defect, in a Ti1−yNbyO2 or a Ti1−yNbyO2+y/2 solid solution, respectively. In the overstoichiometric range of the oxide, the data, when applied to undoped rutile, allow some conclusions about the atomic or electronic transport properties, both in the high and low temperature regimes.

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