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

One-dimensional defects are created in [001] and [110] oriented TiO2 single crystals by uniaxial pressure. Transmission electron microscopy (TEM) characterization shows them to preferably lie on {110} planes. Electrical properties studied as a function of oxygen partial pressure reveal their influence on ionic and electronic charge carriers. At high oxygen partial pressures (1 bar105 bar) the conductivity due to positive charge carriers is strongly enhanced, e.g., the ionic conductivity is increased by more than two orders of magnitude, when the electrical measurement axis lies on the slip plane. In contrary, no changes are observed when the measurement axis does not lie on the slip planes. At low oxygen partial pressures (<1015 bar), irrespective of orientation and presence of dislocation, there is no change in the n-type conductivity. The observed phenomena can be well explained within the space charge model, assuming the dislocation cores to exhibit an excess negative charge (increased titanium vacancy concentration). The present study gives a clear correlation between line defects and point defect concentrations in such an oxide for the first time.