Electrical properties of Nb-doped titanium dioxide TiO2 at room temperature

Abstract

Nb-doped TiO2(0-15 at. % Nb) polycrystalline specimens were prepared by the sol-gel method. Below 10 at. % of Nb, materials were homogeneous and exhibited rutile structure, their lattice parameters changing with Nb concentration according to the Vegard's law. Above 10 at. % of Nb, the second phase TiNb2O7 was formed, detected by X-ray diffractometry. Materials were heated at 1273 K for 3 h in air (Po2= 210 kPa) and in flow of Ar + 3 vol. % H2 gas mixture (pO2 = 10-15 Pa) and then cooled down. Electrochemical impedance spectroscopy within the frequency range 0.01 Hz-2 MHz has been used to determine electrical properties of the materials. An equivalent circuit composed of a resistor Rgh a capacitor C connected parallel and a resistor Rb connected in series, well represents the electrical properties of reduced samples. On the other hand, non-Debye elements should be taken into account in construction of the equivalent circuit of oxidized materials. The mechanism of the Nb incorporation has been proposed.