THE EFFECTS OF DOPANTS AND A-B SITE NONSTOICHIOMETRY ON PROPERTIES OFPEROVSKITE-TYPE PROTON CONDUCTORS

Investigations of perovskite-type BaCeO3 and SrCeO3 with various dopan ts (Y, Gd, Nd, and Ni) indicate that their microstructures and electri cal properties are strongly influenced by the type and amount of dopan ts. Grain growth and densification of sintered samples are influenced by dopant level and A:B site nonstoichiometry. The conductivity of BaC e1-xYxO3-delta increases with the yttrium content in hydrogen and wet Ar, and exhibits a maximum in oxygen at an yttrium content of 10 to 20 %. BaCe0.8Y0.2O3-delta, has the highest conductivity in a hydrogen atm osphere: similar to 1.54 x 10(-2) Omega(-1) cm(-1) at 600 degrees C, a nd similar to 4.16 x 10(-2) Omega(-1) cm(-1) at 800 degrees C. The eff ect of BaO excess depends on the concentration of dopant. Compared wit h BaCe0.95Y0.05O3-delta, doped BaCeO3 with BaO excess (BaO.0.90CeO(2). 0.025Y(2)O(3)) has a higher total conductivity in all atmospheres stud ied (O-2, H-2, and wet Ar), whereas the conductivity of BaCeO3 with ex cess BaO (BaO.0.85CeO(2).0.05Y(2)O(3)) is lower than that of BaCe0.9Y0 .1O3-delta. BaCeO3 based materials have higher conductivities than tho se of SrCeO3 based materials, whereas SrCeO3 based materials show high er proton transference numbers.