Thermoelectric power in reduced pure and Nb-doped TiO2 rutile at high temperature

Abstract

The nature of defects in reduced pure and Nb‐doped TiO2 rutile is investigated at high temperature by Seebeck coefficient measurements. The classical point defect model approach allows a good fit of the theoretical curves to experimental data. In undoped rutile, the main defects should be titanium interstitials in a large oxygen partial pressure range. For small departures from stoichiometry, the influence of impurities and band to band thermal excitation is discussed. In the case of Nb‐doped rutile, two kinds of compensation may occur. Some conclusions related to transport phenomena in such materials are drawn.

Electrical properties of polycrystalline TiO2. Prolonged oxidation kinetics

“…The formation of these defects have been already postulated before [5][6][7][8]. So far, however, the effects related to the formation of these defects were observed for TiO 2 single crystal only [4].…”

Influence of Line Defects on the Electrical Properties of Single Crystal TiO2

“…At intermediate temperatures, nominally undoped rutile single crystals are electronic conductors with very low ionic transference number. [ 27 ] In case of signifi cantly doped rutile the ionic transference number depends on p O 2 ; the number is negligible at very low and high p O 2 and increases at intermediate p O 2 . [ 29 ] Based on simple mass action laws and electroneutrality conditions, the defect concentrations can be related to the oxygen partial pressure ( p O 2 ) when equilibrium with gas phase is established: [ 28 ] …”

“…[ 12 , 15 ] In other studies the same slip systems were found. [ 19 , 20 ] The electrical properties of TiO 2 were studied independently in the past [27][28][29] in slightly and strongly reducing atmosphere where nominally undoped TiO 2 is an n-type conductor, and in oxidizing atmosphere where rutile is p-type conducting. At intermediate temperatures, nominally undoped rutile single crystals are electronic conductors with very low ionic transference number.…”

Electrical properties of polycrystalline TiO2· Thermoelectric power

“…The thermoelectric power data for TiO 2 at elevated temperatures are scarce and limited to several reports [5][6][7][8]. Moreover, there is no consistency between the reported data.…”

“…While [5] these defects may assume different valencies, it has been generally assumed that the defect disorder at elevated temperatures consist predominantly of the following defects:…”