Huge Electrical Conductivity Changes in SrTiO3 upon Reduction of the Grain Size to the Nanoscale

In this contribution, we present the electron conduction properties of nanocrystalline as well as microcrystalline undoped SrTiO3 ceramics obtained over a broad range of oxygen partial pressures (pO2) via impedance spectroscopy. Remarkably, compared to the bulk properties, an increase of the n-type conductivity by almost three orders of magnitude and a decrease of the p-type conductivity by more than three orders of magnitude are observed in the nanocrystalline samples. This generates a shift of the p-n transition (conductivity minimum) by twelve orders of magnitude in terms of oxygen partial pressure. The results can be explained in the light of space charge effects occurring as a consequence of a positive excess charge in the grain boundary core.