Semiconducting properties of polycrystalline titanium dioxide

Semiconducting properties of polycrystalline titanium dioxide TiO₂ (rutile) have been studied using the measurements of both electrical conductivity (EC) and thermopower (TP) in the temperature range 1023-1223 K. The band gap was determined from both the minimum of the electrical conductivity vs. p(O₂) and the Jonker analysis resulting in 3.34 and 3.13 eV, respectively. The observed decrease of the mobility ratio for electronic charge carriers, μ_p/μ_n, with temperature is consistent with the hopping transport mechanism of electrons and the band conduction mechanism of electron holes. This effect, however, is inconsistent with the semiconducting properties reported for TiO₂ single crystal for which the mobility ratio is independent of temperature. The difference between the two is considered in terms of the impact of grain boundaries, and specifically the local structure of the grain boundary layer, on conduction in polycrystalline TiO₂.