ELECTRICAL-CONDUCTIVITY IN NON-STOICHIOMETRIC TITANIUM-DIOXIDE AT ELEVATED-TEMPERATURES

The electrical conductivity of polycrystalline titanium dioxide prepared by a liquid mix technique was measured for the oxygen partial pressure range of 100 to 10-19 atm and temperature range of 850 to 1050°C. The data were found to be proportional to the -1/6 power of oxygen partial pressure for the oxygen pressure range 10-19 to 10-15 atm, and proportional to PO(2)-1/4 for the oxygen pressure range >10-15 atm. The region of linearity where the electrical conductivity varied as the -1/4 power of PO(2) increased as the temperature was decreased. There was evidence of p-type behavior for PO(2)>10-2 atm in the temperature range 950 to 850°C. Electrical conductivity minima in the logσ against log PO(2) plot moved to lower PO(2) as the temperature was decreased in the range 950 to 850°C. The measured oxygen pressure dependence of electrical conductivity in the lowest PO(2) region supports the oxygen vacancy defect model. The observed data are consistent with the presence of small amounts of acceptor impurities. A binding energy of 0.67 eV between the acceptor impurity and its compensating oxygen vacancy was also determined.