Effect of Manganese Distribution on Sensor Properties of SnO₂/MnO_x Nanocomposites

Nanocomposites SnO₂/MnO_x 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.