Mesoscopic electrical conduction in nanocrystalline SrTiO3

Detailed impedance analysis of dense nanocrystalline SrTiO3 ceramics in comparison to microcrystalline samples gives direct and unambiguous evidence of a space charge overlap as a characteristic size effect. Owing to the significant extension of depletion zones for the holes, the bulk impedance signal disappears at about 100 nm grain boundary spacing. In accordance with the increased homogeneity of this mesoscopic situation the remaining signal is characterized by a frequency dispersion of the circuit parameters that is low compared with the microcrystalline samples. Space charge potentials for various sizes are extracted. The conclusions are corroborated by numerical calculations. (c) 2006 American Institute of Physics.