First-principles calculations to investigate doping effects on electrical conductivity and interfacial contact resistance of TiO2

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 calculation merged with Boltzmann transport theory and Schottky-Mott theory is used to study the doping effects of thirty-seven elements on the electrical conductivity and the Schottky barrier. The effect of doped concentration on the conductivity was also investigated. The results indicate the low electrical conductivity of TiO2 is attribute to strong ionic bond of Ti-O. The covalent bond between dopant and O atoms is found to enhance at a higher doped concentration. That can lead to the extension of the unoccupied state of valence band maximum and conduction band minimum to the forbidden gap, which further leads to the reduction of the band gap. In addition, 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. The mechanism of doped modifications was further studied to guide experimental works.