Electrical and defect thermodynamic properties of nanocrystalline titaniumdioxide

The electrical properties of dense nanocrystalline TiO2 ceramics with an av erage grain size of 35 nm were investigated by impedance spectroscopy and c ompared with a coarsened material with micron size grains. The nanocrystall ine ceramics show an uncommon domain of ionic conductivity at high oxygen p ressures and a steep increase of electronic conductivity at low oxygen pres sures. These results are discussed in terms of defect chemical models. The enthalpy of reduction of the nanocrystalline TiO2 was deduced to be signifi cantly lower than that of the coarsened material. This may be related to lo wer defect formation energies at interface sites. (C) 1999 American Institu te of Physics. [S0021-8979(99)07901-3].