Ionics 8 (2002) 293 Influence of Acceptor Doping on Ionic Conductivity in Alkali Earth Titanate Perovskites L.A. Dunyushkina, E.A. Mashkina, I. Yu. Nechaev, A.A. Babkina, N.O. Esina, B.V. Zhuravlev and A.K. Demin Institute for High Temperature Electrochemistry Ural Division of Russian Academy of Science S. Kovalevskoy Str. 22, 620219 Ekaterinburg, Russia Abstract. The electrical conductivity of the SrTil.xFexO3-8, BaTil_xFexO3.8 and SrTil_xMnxO3_8 systems has been studied in a range of oxygen partial pressures between 10-16 and 0.21 atm at 900 and 1000 ~ The materials exhibit predominantly ionic conductivity in a wide range of intermediate oxygen partial pressures. It has been found that in Fe doped strontium and barium titanates, the dependencies of the ionic conductivity on the acceptor concentration show a local maximum near x = 0.2. Taking into account that in the CaTil.xFexO3.ssystem (x = 0- 0.5), the concentration dependence of the ionic conductivity also has a maximum near x = 0.2, it caq be concluded that this is a common phenomenon for Fe doped alkali earth titanates. An assumption has been made that a scheme of defect formation devised earlier for Fe doped calcium titanate is applicable for other alkali earth titanates. 1. Introduction The perovskite-type titanates show high levels of ionic and electronic conductivities and significant thermal, che- mical and mechanical stability in a wide range of oxygen activities. Due to these properties, the titanates have a lot of potential applications as electrodes for high tempera- ture fuel cells and other electrochemical devices, cata- lysts, oxygen permeable membranes for oxygen separa- tion and hydrogen production. Undoped alkali earth titanates exhibit a rather low ionic conductivity. According to the defect model elabo- rated in [1-3], oxygen vacancies and electrons (holes) the main mobile species in these materials. It is known that doping of titanate perovskites with different elements has profound effects on the structural, chemical and physical properties of the materials. It has been found that Fe-substitution in Ti-sites results in improvement of the electrical properties of calcium and strontium tita- nates, because the acceptor doping is accompanied by the formation of oxygen vacancies and electron charge carriers [4-11 ]. The results of the studies of the electrical properties of iron-doped calcium titanate were reported in [4-6]. According to these data, the ionic conductivity has a maximum near the dopant concentration of x = 0.2 at high temperatures. A few studies of crystal structure evolution under Fe- substitution in CaTiO3 system have been performed by means of electron microscopy, transmission electron microscopy and X-ray diffraction [12-14]. According to the results of electron microscope investigations and X- ray diffraction of Ca2Ti2.2xFe2xO6. x solid solutions re- ported in [12], at low iron concentrations (x < 0.4) oxy- gen vacancies are randomly distributed in the crystal lattice, while at higher iron concentrations (x > 0.55) the vacancy ordering occurs. X-ray diffraction does not show long-range ordering of the oxygen vacancies in the region of x = 0.05 - 0.38 in CaTil_xFexO3.x/2 system, which