Electrical properties of polycrystalline TiO2: Equilibration kinetics

Abstract

The equilibration kinetics was determined for high purity polycrystalline TiO 2 in the temperature range of 1,123-1,323 K, within a wide range of oxygen activity, 10 −13 Pa < p(O 2 ) < 75 kPa. The equilibration kinetics experiments were performed within narrow p(O 2 ) ranges. The obtained kinetic data were used for the determination of the chemical diffusion coefficient, D chem , which exhibits a complex dependence of p(O 2 ). The D chem data are considered in terms of the effect of defect disorder on the mass transport kinetics in the chemical potential gradient. The reported diffusion data may be used for prediction of optimized processing conditions required to impose a homogeneous distribution of oxygen activity within the TiO 2 specimen.

Electrical properties of polycrystalline TiO2. Prolonged oxidation kinetics

“…It has been shown before [3] that the rate of a surface reaction is substantially faster than the bulk diffusion in the Regime I. Consequently, the effect of the surface reaction on the equilibration kinetics in the Regime II, which is substantially slower than that in the Regime I, must be ruled out.…”

“…This indicates that the prolonged oxidation leads to an increase in the concentration of acceptor-type centres at the gas/solid interface, which are then propagated into the bulk leading to imposition of uniform concentration. Figures 3 and 4 show the electrical conductivity changes in the Kinetic Regime II and the related equilibration degree defined as [3,4]:…”

“…The second part [2], which determined the effect of oxygen activity on thermoelectric power for the same TiO 2 specimen, provides the verification of the defect disorder models derived in part I. The third part studies the equilibration kinetics during isothermal oxidation and reduction of polycrystalline TiO 2 in the temperature range 1,123-1,323 K and the related chemical diffusion coefficient, D chem , within narrow ranges of oxygen activity [3]. The determined diffusion data indicate that D chem exhibits a strong dependence on oxygen activity.…”

“…The present study, including the present work and the former three papers [1][2][3], aims at the characterisation of well-defined polycrystalline TiO 2 in terms of the defect disorder and its impact on properties, including semiconducting properties and chemical diffusion. The first part of the present study reported the effect of oxygen activity on electrical conductivity for high purity polycrystalline TiO 2 [1].…”

Electrical properties of polycrystalline TiO2· Thermoelectric power

“…Both electrical conductivity and thermoelectric power are applied for monitoring the gas/solid kinetics. The determined kinetic data are then used for the determination of the chemical diffusion coefficient [10].…”