Electrical properties of polycrystalline TiO2· Thermoelectric power

Abstract

The present work determined thermoelectric power for high-purity polycrystalline TiO 2 at elevated temperatures (1,123-1,323 K) and in the gas phase of controlled oxygen activity, 10 −13 Pa < p(O 2 ) < 10 5 Pa. The slope of the thermoelectric power vs log p(O 2 ) is 1/10, instead of 1/6 expected by the theory and observed for TiO 2 single crystal. The discrepancy between the two is considered in terms of the effect of the local grain boundary structure on thermoelectric power. A comparison between the electrical conductivity and thermoelectric power data indicates that the oxygen activity values related to the n-p transition point determined by thermoelectric power are lower than those determined by electrical conductivity.

Electrical properties of polycrystalline TiO2. Prolonged oxidation kinetics

“…The high temperature Seebeck probe was applied for the determination of the electrical conductivity [1], σ , and thermoelectric power, S [2]. The isothermal equilibration kinetic was determined at 1,323 K and at p(O 2 ) = 75 kPa over the period of a thousand hours.…”

“…That work led to derivation of defect disorder models for TiO 2 . 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 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].…”

Defect engineering of titanium dioxide: full defect disorder

“…[3][4][5][6] Although the diagrams presented in this paper were constructed for temperatures 1073 and 1323 K as an example, similar diagrams may be developed for any temperature within the validity limit of the equilibrium constant in Table 1. The experimental data used for this illustration were determined at 1223 K.…”

Semiconducting Properties of Oxidized and Reduced Polycrystalline TiO2. Jonker Analysis

“…Their influence ultimately leads to the nÀp transition, which is revealed in the high-p(O 2 ) range (change to positive values of thermoelectric power). These data are discussed in more details in ref 8.…”