Grain boundary blocking and segregation effects in yttrium-doped polycrystalline titanium dioxide

Impedance spectroscopy was used to investigate the electrical behavior of undoped, 0.025 mol% and 0.1 mol% yttrium-doped polycrystalline TiO2. In the doped samples, distinct contributions from the bulk and grain boundaries to the electronic conduction were evident, while no grain boundary blocking effect was observed in pure titania samples. The activation energy for grain boundary electronic conduction increased with increasing dopant concentration, which implied an increasing barrier height in these regions introduced by the solute interfacial excess. The impedance behavior was correlated with grain boundary solute segregation measurements and rationalized in terms of the local grain boundary defect chemistry in the grain boundary cores and space-charge layers.