Nanocomposites SnO2/MnOx with various manganese content (up to [Mn]/[Sn] = 10 mol. %) and different manganese distribution were prepared by wet chemical technique and characterized by X-ray diffraction, scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis and mapping, IR and Raman spectroscopy, total reflection X-ray fluorescence, mass-spectrometry with inductive-coupled plasma (ICP-MS), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) spectroscopy. A different distribution of manganese between the volume and the surface of the SnO2 crystallites was revealed depending on the total Mn concentration. Furthermore, the identification of surface MnO2 segregation was performed via Raman spectroscopy. There is a strong dependence of the sensor signal toward CO and, especially, NO) on the presence of MnO2 surface segregation. However, manganese ions intruding the SnO2 crystal structure were shown to not almost effect on sensor properties of the material.
Keywords: carbon monoxide; manganese doping; microstructure effect; nanocrystalline tin oxide; nitrogen oxide; surface modification; thermally activated gas sensor.