P. Lupetin and G. Gregori
The grain size plays a fundamental role in the determination of the electrical properties of electroceramic oxides. Notably, at the nanoscale the grain boundaries are predominant over the bulk and they fully control the overall conduction properties. Therefore, the conduction mechanism may be completely different if one compares the nanoscale with the macroscale.
We study strontium titanate (SrTiO3) which is an excellent model material for electroceramic oxides and perovskites, thanks to its pronounced stability and its well explored defect chemistry at the macroscale and we investigate its conduction properties over a broad range of oxygen partial pressures via impedance spectroscopy, since the oxygen non-stoichiometry is the key parameter in determining whether this perovskite is p-type, n-type or ionic conductor.
Several exciting size-induced phenomena have already been observed in the undoped material: increase of n-type conductivity by several orders of magnitude, an equally great depression of p-type conductivity and a shift of the p-n transition of 12 orders of magnitude in terms of oxygen partial pressure (Fig. 1).