Design of ceramic materials for chemical sensors:: SmFeO3 thick films sensitive to NO2

Ultrafine SmFeO(3) powders were prepared by the thermal decomposition at 700 degrees C of the corresponding hexacyanocomplex, Sm[Fe(CN)(6)]. 4H(2)O. These powders were used for the preparation of pastes which were deposited as thick films on alumina substrates with comb-type Au electrodes. The films were fired at different temperatures in the 800-1000 degrees C range. The content of alpha-terpineol, a component of the organic vehicle, was varied in the range 0.0046-4 wt%, The microstructure, the chemical composition at the surface, the electrical conductivity, and the NO(2) sensing properties of the films were investigated. The content of alpha-terpineol strongly influenced the electrical conductivity and its activation energy, A significant reduction in the NO(2) response was observed for the films containing smaller amounts of alpha-terpineol, together with an increase in conductivity. On the other hand, the largest NO(2) response was observed for the films fired at 1000 degrees C when 4 wt% of alpha-terpineol was used. Such increase in conductivity is attributed to a different oxygen surface layer on the SmFeO(3) surface, which is induced by the decomposition reaction of alpha-terpineol during sintering, The materials processing parameters are thus of primary concern for the NO(2) sensing properties of the SmFeO(3) thick films. The correlations found between activation energy, NO(2) sensitivity, and materials characteristics (influenced by the preparation parameters) are reported. These correlations can be used to design the gas-sensing properties of SmFeO(3) thick films for the optimization of their sensing characteristics.