Synthesis and electrical properties of K- and Pr-substituted LaGaO3 and LaInO3 perovskites

Replacement of divalent Sr2+ ions by monovalent K+ ions in La0.9Sr0.1Ga0.8M g0.2O2.(85) (LSGM) decreases the electrical conductivity of LSGM and increa ses the activation energy to 1.42 eV. Substitution of La by substantial amo unts of up to 50 atom % of Pr in LSGM yields new mixed oxide ion and electr onic conductors. Substitution of 50 atom % Pr for La in the In-analog of LS GM, La0.9Sr0.1In0.8Mg0.2O2.85 (LSIM), does not increase the electrical cond uctivity. Among the investigated oxides, La0.4Pr0.4Sr0.2In0.8Mg0.2O2.8 exhi bits the lowest activation energy of 0.44 eV and the highest electrical con ductivity of 3.17 x 10(-5) S/cm at 200 degreesC. Oxygen partial pressure de pendence of the electrical conductivity reveals that LSIM and Pr-substitute d LSIM perovskites are mixed oxide ion and p-type electronic conductors at high oxygen partial pressures. The electronic conductivity increases with i ncreasing Pr content in LSIM. Open-circuit voltage measurements employing L a0.45Pr0.45Sr0.1Ga0.8Mg0.2O2.85 as separator in the galvanic cell H(2)paral lel to air show that the average transference number (t(O)(2-)) for oxide i on conduction is 0.78-0.90 in the temperature range 450-650C. Powder X-ray diffraction data reveal that LSIM and Pr-substituted LSIM perovskites are n ot stable at low oxygen partial pressures of about 10(-22) atm, while Pr-su bstituted LSGM retains the cubic perovskite structure. Accordingly, the new materials reported here may find application as electrode materials for so lid oxide fuel cells and oxygen sensors. (C) 2001 The Electrochemical Socie ty.