Synthesis, physicochemical characterization and ionic conductivity of LaGa0.4Mg0.2M0.4O3-δ (M = Cr, Mn, Fe, Co)

Partial electronic and ionic conductivities, crystal structure, thermal expansion and infrared absorption spectra of the perovskite-type series, LaGa0.40Mg0.20M0.40O3-delta (M = Cr, Mn, Fe, and Co), have been studied. The rhombohedral distortion of the perovskite lattice decreases and the unit cell volume increases in the sequence Co < Cr < Mn < Fe. The p-type electronic conduction increases with atomic number of the transition metal cation; the activation energy varies in air from 15.9 to 32.1 kJ/mol. The oxygen ionic conductivity of the M-doped phases at temperatures below 1200 K is significantly lower than that of LaGa(Mg)O-3. The highest ionic conductivity was found for the Fe- and Co-containing phases. The ion transference numbers of La(Ga,Mg,M)O3-delta at 970-1270 K were determined to vary in a wide range, from 2 x 10(-5) to 3 x 10(-2). Thermal expansion coefficients, calculated from the dilatometric data collected in the temperature range 300-1100 K, lie in the range (7.2-15.5) x 10(-6) K-1.