Charge Transport in Cr-Doped Titanium Dioxide

The present work reports the effect of chromium on the mobility terms for electrons and electron holes for TiO2 at 1273 K. These data were determined by using the concentration data from the defect disorder diagram derived by the authors and the electrical conductivity data for Cr-doped TiO2 reported by Carpentier et al. [J. Phys. Chem. Solids 1989, 50, 145]. It is shown that chromium incorporates into the TiO2 lattice according to two different mechanism depending on chromium concentration. In the concentration range 1−3 atom %, chromium incorporation leads to the formation of acceptors, which are compensated by tri-valent titanium interstitials. However, in the range 4−5 atom %, the acceptor-type defects formed by chromium incorporated in the titanium sites are compensated by oxygen vacancies. The incorporation of chromium results in a relatively insignificant increase of the mobility of electrons from μn = 0.5 × 10-5 m2 V-1 s-1 for undoped TiO2 to μn = 1.3 × 10-5 m2 V-1 s-1. The incorporation of Cr results in a drop of the mobility of electron holes from μp = 2.95 × 10-5 m2 V-1 s-1 for undoped TiO2 to μp = 0.6 × 10-5 m2 V-1 s-1 for Cr-doped TiO2. The observed mobility changes are considered in terms of the Cr-induced structural changes of the TiO2 lattice.