Influence of cobalt and iron additions on the electrical and thermal properties of (La,Sr)(Ga,Mg)O3-δ

(La,Sr)(Ga,Mg)O3-delta (LSGM) perovskite compositions doped with Co or Fe were prepared by a combustion synthesis technique. Small doping levels of Co or Fe (less than or equal to 10 mol% on the B-site) resulted in increased electrical conductivity at low temperatures (due to the introduction of electronic charge carriers into the lattice), but at high temperatures the electrical conductivity was dominated by ionic conduction and was similar in magnitude to that of the base LSGM composition. Higher additions of Co or Fe resulted in much higher electrical conductivity in which the electronic component was dominant. A reversible weight loss at elevated temperatures was observed in all of the compositions as the lattice oxygen stoichiometry decreased with increasing temperature. This loss of lattice oxygen correlated with a reduction in the rate of increase (or even a net decrease) in electrical conductivity with increasing temperature. This behavior was attributed to the elimination of electronic charge carriers (and a reduction in valence of some of the Co or Fe cations in the material) as lattice oxygen vacancies were formed. The thermal expansion of the materials increased substantially with increasing Co content, while only slight increases in thermal expansion were observed with increasing Fe content. (C) 2000 The Electrochemical Society. S0013-4651(00)01-088-0. All rights reserved.