Gas-sensitive features of Fe₂O₃-based materials are essentially influenced by structural features of Fe₂O₃ and its concentration in oxide composite. Doping SnO₂ and In₂O₃ with Fe³⁺ ions results in increase of the layer resistance and decrease of sensitivity of the corresponding sensors to the most of gases. When Fe₂O₃ content reaches 50 mol % or more, gas-sensitive behaviour of the materials becomes hardly predictable. However, there are definite links between the functional characteristics of such materials and their structural features. In this work we reported the established correlations. The films were formed from colloid solutions of co-precipitated hydroxides of Fe and In. The sol-gel technique allows obtaining the oxide composites with required structure. Two types of samples were obtained: Fe₂O₃-In₂O₃ (9:1) prepared by using Fe³⁺ inorganic salt (sample I), and via less common Fe²⁺ precursor (sample II). The structure of the composites was characterised by XRD, TEM/ED and Mössbauer spectroscopy. The sample I remains X-ray amorphous up to 300 C; it consists of isometric particles of 2-6 nm. According to the XRD and ED data, the particles consist of solid solution of In³⁺ in α-Fe₂O₃ lattice. In contrast, sample II consists of grains, which differ in shape and size. Thus, along with fine particles, the grains with well-defined textures and growth anisotropy are present. ED examination of the sample II revealed highly dispersive α-Fe₂O₃ and γ-Fe₂O₃ phases. Thin films of Fe₂O₃-In₂O₃ (9:1) composites of the same chemical composition with homogeneous (sample I) and heterogeneous (sample II) structures differ essentially by gas-sensitive behaviour. The sample I are practically insensitive to NO₂ (0.5 ppm), CO (50 ppm) and C₂H₅OH (50 ppm). In contrast, the sample II demonstrates much greater response to the indicated gases. This work was supported by the projects GASMOH (2000-10041) and INTAS (2000-0066).

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