Abstract:A series of new perovskite-type mixed conducting ceramics Sm_1-xSr_xAl_1-yFe_yO_3-δ (SSAF) were prepared by the organic gel method combined with solid state sintering technique. The thermal decomposition and phase inversion processes of the gel precursors and phase structure of the sinters were analyzed by means of TG—DTA, XRD and FTIR. The relative density of the ceramics was measured by Archimedes method, and the electrical conductivity of the samples in air was studied by the direct current four-wire method. The effects of sintering temperature and concentrations of Sr and Fe on the structures, electrical properties and transport mechanism of the samples were investigated. The results show that the well-crystallized nanopowders with tetragonal perovskite structure can be obtained by calcining the gel precursors at 900 ℃ for 5 h. With increasing the sintering temperature, both the electrical conductivity and relative density of SSAF9155 ceramics become large initially and then decrease, and the sample sintered at 1 450 ℃ for 5 h has the highest relative density and electrical conductivity. The electrical conductivities of SSAF ceramics are dominated by p-type electronic conduction and increase with increasing Sr and Fe doping content. Besides, the electrical conductivities of these samples increase with increasing temperature in medium-low temperature region and obey the Arrhenius relationship, indicating that the mechanism of electronic transport is the hopping of p-type small polaron. The apparent activation energies for SSAF ceramics decrease with increasing Fe doping content, but increase with increasing Sr doping content.

Key words: conducting ceramics; Sr; Fe; doping; SmAlO₃; organic gel method; electrical property