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

(La,Sr)(Ga,Mg)O3-delta (LSGM) perovskite compositions doped with Co or Fe w ere 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 ele ctronic charge carriers into the lattice), but at high temperatures the ele ctrical conductivity was dominated by ionic conduction and was similar in m agnitude to that of the base LSGM composition. Higher additions of Co or Fe resulted in much higher electrical conductivity in which the electronic co mponent was dominant. A reversible weight loss at elevated temperatures was observed in all of the compositions as the lattice oxygen stoichiometry de creased with increasing temperature. This loss of lattice oxygen correlated with a reduction in the rate of increase (or even a net decrease) in elect rical conductivity with increasing temperature. This behavior was attribute d to the elimination of electronic charge carriers (and a reduction in vale nce of some of the Co or Fe cations in the material) as lattice oxygen vaca ncies were formed. The thermal expansion of the materials increased substan tially with increasing Co content, while only slight increases in thermal e xpansion were observed with increasing Fe content. (C) 2000 The Electrochem ical Society. S0013-4651(00)01-088-0. All rights reserved.