Thermo-electric and conductive properties of blue titanium dioxide

A simple theory of thermoelectric effects in semi-conductors is developed. It is shown how measurements of thermopower at various temps. can be interpreted in terms of the concentration of free charge carriers (electrons or positive holes) and their activation energy. Special attention is given to the disturbing effect of non-uniformities in the impurity content on the experimental results. From a comparison of thermoelectric and resistive properties for a series of specimens, conclusions can be drawn as to the relative magnitude of intergranular resistances and the bulk resistivity of individual grains. The thermoelectric properties of TiO2 (containing a stoichiometric excess of metal) were found to be in substantial agreement with theoretical prediction between 97degK and 617degK. The activation energies thus evaluated were, however, those obtained from the measurement of resistivity at different temps. This and other problems in connection with the interpretation of activation energies are discussed in the light of Lichtenecker's theory of solid mixtures.