Electrical and defect thermodynamic properties of nanocrystalline titanium dioxide

The electrical properties of dense nanocrystalline TiO2 ceramics with an average grain size of 35 nm were investigated by impedance spectroscopy and compared with a coarsened material with micron size grains. The nanocrystalline ceramics show an uncommon domain of ionic conductivity at high oxygen pressures and a steep increase of electronic conductivity at low oxygen pressures. These results are discussed in terms of defect chemical models. The enthalpy of reduction of the nanocrystalline TiO2 was deduced to be significantly lower than that of the coarsened material. This may be related to lower defect formation energies at interface sites. (C) 1999 American Institute of Physics. [S0021-8979(99)07901-3].