Electrical conductivity in non-stoichiometric titanium dioxide at elevated temperatures

Abstract

The electrical conductivity of polycrystalline titanium dioxide prepared by a liquid mix technique was measured for the oxygen partial pressure range of 10° to 10⁻¹⁹ atm and temperature range of 850 to 1050° C. The data were found to be proportional to the −1/6 power of oxygen partial pressure for the oxygen pressure range 10⁻¹⁹ to 10⁻¹⁵ atm, and proportional to $P_{{\text{O}}_2 }^{ - 1/4}$for the oxygen pressure range >10⁻¹⁵ atm. The region of linearity where the electrical conductivity varied as the −1/4 power of $P_{{\text{O}}_2 }$increased as the temperature was decreased. There was evidence of p-type behaviour for $P_{{\text{O}}_2 } > 10^{ - 2}$atm in the temperature range 950 to 850° C, although the measured data were insufficient to assign a pressure dependence. Electrical conductivity minima in the log σ against log $P_{{\text{O}}_2 }$plot moved to lower $P_{{\text{O}}_2 }$as the temperature was decreased in the range 950 to 850° C. The measured oxygen pressure dependence of electrical conductivity in the lowest $P_{{\text{O}}_2 }$region supports the oxygen vacancy defect model. The observed data are consistent with the presence of very small amounts of acceptor impurities. A binding energy of ∼ 0.67 eV between the acceptor impurity and its compensating oxygen vacancy was also determined.