Temperature- and oxygen partial pressure-dependent electrical conductivity in nanoporous rutile and anatase

The dependence of the electrical conductivity (σ) of sintered nanoporous TiO2 (rutile and anatase) layers on temperature (T) and partial pressure of oxygen (pO2) has been studied by impedance spectroscopy for T up to 450 °C and pO2 up to 10−5 mbar. The diameter of the TiO2 nanoparticles was changed between 5 and 60 nm. σ is thermally activated with EA=0.85 eV independent of the absolute value of σ and depends on pO2 by power law for pO2<1–10 mbar. The electrical properties of reduced nanoporous TiO2 are determined by surface chemical reactions which lead to the formation of shallow donor and deep trap states.