Electron transport in Ti 1−xNb xO 2 solid solutions with x < 4%

Abstract

By means of conductivity and thermopower measurements in niobium doped rutile TiO 2, we have analysed the electron transport. A previous study made in TiO 2 pointed out the existence of a large polaron transport. Nevertheless, some uncertainties remain as the precise dependence of the mobility with the temperature. The Nb doped TiU 2 studied in the present paper brings some new information: the mobility could follow an optical phonon scattering law. The FHIP model seems to be the more appropriate model to describe the mobility but the lack of theoretical calculation of transport energy does not allow definitive conclusions about the physical processes which occur in the intermediate range of temperature. However, we can say that the ionization activation energy of Nb is found to be close to 14 eV. Moreover, it is found that the localized electrons become mobile by hopping with increasing niobium content. This yields a conductivity composed by electrons which move in the 3 d Ti band and localized electrons which hop from site to site. This hopping component and the number of localized electrons increase with niobium content. This leads to the disappearance of the band motion in the conductivity.