The properties of dense nanocrystalline ceramics with an average grain size of 35nm were investigated by means of impedance spectroscopy and were compared with those of a coarsened sample having micron-sized grains. The nanocrystalline ceramics exhibited an unusual domain of ionic conductivity (figure 5) at high O pressures, and a sharp increase in electronic conductivity at low O pressures. The results were explained in terms of defect chemical models. The enthalpy of reduction of the nanocrystalline material was deduced to be significantly lower than that of the coarsened material. This was attributed to lower defect formation energies at interface sites.

Electrical and Defect Thermodynamic Properties of Nanocrystalline Titanium Dioxide. Knauth, P., Tuller, H.L.: Journal of Applied Physics, 1999, 85[2], 897-902