Analysis of doping effects on electrical conductivity and interfacial contact resistance of TiO2

Abstract

In fuel cells, electrolysis cells, etc., titanium have been widely employed due to the high corrosion resistance achieved by the oxide film. But it also leads to low electrical conductivity and reduces the cells efficiency significantly. To illuminate how to improve the conductivity of titanium alloys, first-principles calculations merged with Boltzmann transport equation and Schottky-Mott theory is adopted to investigate the doping effects of thirty-seven elements on the electronic transport property. The results indicate the low electrical conductivity of TiO2 is attribute to the strong ionic bond of Ti-O. Nb, Ta, Sb and Zr can enhance the conductivity to above 1.0×103 S∙cm-1, which can also make the Schottky barrier decline from 1.05 eV to below 0.4 eV. That is mainly due to the Fermi level shifting and the stronger covalent bond formed between the impurity and O atoms. This work also investigated the effect of doping ratio on the conductivity. The covalent bond between impurity and O atoms is found to increase at a higher doped ratio. That results in the extension of the unoccupied state of the valence band maximum and conduction band minimum to the forbidden gap, which further leads to the reduction of the band gap.