PREPARATION AND CHARACTERIZATION OF PR1-XSRXMNO3+ -DELTA IS (X=0, 0.15, 0.3, 0.4, 0.5) AS A POTENTIAL SOFC CATHODE MATERIAL OPERATING AT INTERMEDIATE TEMPERATURES (500-700-DEGREES-C)/

The crystal structure, thermal expansion and electrical conductivity o f Sr-doped praseodymium manganites (Pr1-xSrxMnO3+/-delta where x=0, 0. 15, 0.3, 0.4, 0.5) were studied in air, and their potential use as cat hodes in intermediate temperature SOFCs was evaluated. All composition s have an orthorhombic perovskite-type structure (Pbnm space group). T he lattice parameters were determined at room temperature by X-ray pow der diffraction. The thermal expansion is almost linear for compositio ns with x greater than or equal to 0.15. The electrical conductivity c an be described by the small polaron hopping conductivity model. The c onductivity increases with temperature for all compositions. Both the thermal expansion coefficient (TEC) and the electrical conductivity in crease with increasing Sr content, while the activation energy decreas es. The low values of the calculated activation energies are in agreem ent with the small polaron hopping mechanism. Among the compositions s tudied, Pr0.5Sr0.5MnO3+/-delta, with a TEC value of 12.2 x 10(-6) cm ( cm degrees C)(-1) and a conductivity value of 226 S cm(-1) at 500 degr ees C, seems to be the most promissing material that can function as c athode in the intermediate temperature SOFC. (C) 1997 Elsevier Science Limited.