Nanocomposites SnO₂/SiO₂:SiO₂ Impact on the Active Centers and Conductivity Mechanism

This paper is focused on the effect of the stabilizing component SiO₂ on the type and concentration of active sites in SnO₂/SiO₂ nanocomposites compared with nanocrystalline SnO₂. Previously, we found that SnO₂/SiO₂ nanocomposites show better sensor characteristics in CO detection (lower detection limit, higher sensor response, and shorter response time) compared to pure SnO₂ in humid air conditions. Nanocomposites SnO₂/SiO₂ synthesized using the hydrothermal method were characterized by low temperature nitrogen adsorption, XRD, energy dispersive X-ray spectroscopy (EDX), thermo-programmed reduction with hydrogen (TPR-H₂), IR-, and electron-paramagnetic resonance (EPR)-spectroscopy methods. The electrophysical properties of SnO₂ and SnO₂/SiO₂ nanocomposites were studied depending on the oxygen partial pressure in the temperature range of 200-400 °C. The introduction of SiO₂ results in an increase in the concentration of paramagnetic centers Sn³⁺ and the amount of surface hydroxyl groups and chemisorbed oxygen and leads to a decrease in the negative charge on chemisorbed oxygen species. The temperature dependences of the conductivity of SnO₂ and SnO₂/SiO₂ nanocomposites are linearized in Mott coordinates, which may indicate the contribution of the hopping mechanism with a variable hopping distance over local states.