Electronic transport properties and electronic structure of TiO2-doped YSZ

Electronic conductivity of yttria-stabilized zirconia (YSZ) doped with 2 mol% of TiO2 was measured by the dc-polarization technique using the Hebb–Wagner’s asymmetric cell. The X-ray absorption spectroscopy (XAS) was also employed for 2, 5 and 10 mol% of TiO2-doped YSZ in order to investigate the electronic structure near the band gap. The partial conductivity of conduction electrons equilibrated at unit oxygen partial pressure (σn∘) increased with increasing TiO2 concentration and the apparent activation energy of σn∘ decreased by the TiO2 doping. In contrast, the partial conductivity of holes and the apparent activation energy were almost independent of TiO2 concentration. These results suggest the band-gap narrowing by TiO2 doping, which is consistent with the results of the X-ray absorption spectroscopy measurements, where unoccupied t2g states of Ti3d below the conduction band grew with the increase of the TiO2 concentration. The change in the electronic conductivity with TiO2 concentration was discussed based on the percolation theory.