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 TiO 2 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 TiO 2 reported by Carpentier et al. [ J. Phys. Chem. Solids 1989, 50, 145]. It is shown that chromium incorporates into the TiO 2 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 μ n = 0.5 × 10 -5 m 2 V -1 s -1 for undoped TiO 2 to μ n = 1.3 × 10 -5 m 2 V -1 s -1 . The incorporation of Cr results in a drop of the mobility of electron holes from μ p = 2.95 × 10 -5 m 2 V -1 s -1 for undoped TiO 2 to μ p = 0.6 × 10 -5 m 2 V -1 s -1 for Cr-doped TiO 2 . The observed mobility changes are considered in terms of the Cr-induced structural changes of the TiO 2 lattice.