Hall Effect and Thermoelectric Power in Semiconductive TiO2

The electrical properties of the conductive TiO 2 (rutile) ceramics, as well as single crystals, doped with Nb 2 O 5 or Ta 2 O 5 were investigated by Hall effect and thermoelectric power measurements. These properties were shown to be strongly dependent on the doping concentration which covered the range up to 4 mole-percent. The experimental results indicate that the specimens are non-degenerated n -type semiconductor with a density-of-states effective mass of m * =20 m . At room temperature, where lattice scattering plays a dominant role, Hall mobility is about 0.4 cm 2 /Vs. for lower doping level and it falls down to 10 -2 cm 2 /Vs. with the increasing doping concentration. The mobility increases in the slightly doped specimens at liquid nitrogen point, while it decreases in the specimens doped more heavily than 0.1 mole-percent. The activation energy of the donor centers due to the doping is 0.02 eV. The reduced specimen not intentionally doped, shows a shallower level nearly equal to 0.01 eV.