The electrical conductivity of rutile doped with 0.3–3at%Ta or 0.1–1at%Cr was reported as a function of oxygen pressure at 1273 to 1623K. The results were discussed in terms of a point defect model, on assuming a charge compensation of foreign impurities by usual lattice point defects. In the case of Ta-doped materials, two kinds of charge compensation by an electronic or a lattice defect may occur, according to the oxygen pressure and temperature, the essential features of which were in good agreement with the theoretical analysis. While chromium was incorporated as a trivalent species under a reducing atmosphere, the lack of ionic conductivity due to compensating lattice defects prevents any definitive conclusion about the valence state of the foreign chromium cations under oxidizing conditions. Some additional information and some conclusions were drawn concerning the transport properties of pure or doped titanium dioxide at high temperature.

Electrical Properties and Defect Structure of Rutile Slightly Doped with Cr and Ta. Tani, E., Baumard, J.F.: Journal of Solid State Chemistry, 1980, 32[1], 105-13