The heterogeneous nanometer-scaled oxide materials M1O-M2O (nanocomposites) has pronounced advantages for solid state gas sensor applications. The electronic properties of grain boundaries in two-phase systems are very sensitive to the atmosphere composition. The solid-gas interaction in such systems involves selective chemical reactions on the M1O-M2O grain boundaries. If M2 is a transition metal, the solid-gas interaction may change its oxidation state and distribution between the surface and lattice positions. The behaviour of SnO₂-M2O nanocomposites (M2O = Fe₂O₃, NiO, CuO, PdO, PtO₂, RuO₂) in relation with gas sensing phenomena has been analysed. The work includes the methods of SnO₂ thin and thick films elaboration, investigation of microstructure, surface state and electrical behaviour of nanocomposites in different atmospheres. The mechanism of solid-gas (CO, H₂, CH₄, C₂H₅OH, H₂S, NO₂) interaction is discussed on the basis of results of Mössbauer and Raman spectroscopy, AES, XPS, XAS and conductance measurements. The main information was obtained by in situ techniques. Depending on the ionic radius and charge the M2 elements are variously distributed between the bulk and surface of nanometer-scaled SnO₂ grains. In air all regarded elements being distributed in SnO₂ matrix are in oxidised state. The common points for all nanocomposites studied are: (i) in nanocoposites the SnO₂ grain size is reduced, that can be caused by M2O segregation on SnO₂ grain surface leading to kinetic limitations of recrystallisation processes; (ii) M2O affect the SnO₂ electrical properties, however the mechanism of resistance growth may be different: the compensation effect or barrier formation at the grain joints. At the same time, M2O brings the special properties. They can be involved in specific chemical interactions with the particular gas.
This work was financially supported by INTAS 2000-0066 and RFBR 03-03-32586 grants.

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1. CRYSTALLITE SIZE EFFECT ON THE CONDUCTIVITY OF THE NANOCRYSTALLINE CERAMIC SnO2 AND In2O3