SPACE-CHARGE SEGREGATION AT GRAIN-BOUNDARIES IN TITANIUM-DIOXIDE .1. RELATIONSHIP BETWEEN LATTICE DEFECT CHEMISTRY AND SPACE-CHARGE POTENTIAL

The electrical potential difference between the interface and the bulk in TiO2 is obtained as a function of temperature, oxygen pressure, and acceptor or donor doping from a space charge model that explicitly includes the high-temperature lattice defect chemistry. Using defect equilibrium constants for TiO2 from previous literature studies, it is shown that for a space charge determined by ionic defect equilibration with the interface, the potential is negative in undoped and acceptor-doped TiO2 and positive at high donor concentrations. The isoelectric point lies in the donor-doped regime at high temperatures due to the contribution of defects from reduction, even for fairly oxidizing ambients.