Phase characterization and electrical conductivity of LaSr(GaMg)1−xMnxO3 system

LSGM (La0.9Sr0.1Ga0.8Mg0.2O3) and LSM (La0.9Sr0.1MnO3) are attractive electrolyte and electrode materials, respectively, for the solid oxide fuel cells (SOFCs). Since both materials are based on perovskite structure, the reaction between them is easily expected. In this study, various compositions of LaSr(GaMg)1−xMnxO3 or xLSM–(1−x)LSGM (x=0–1) system were prepared to identify the possible reaction products and to see their effects on the electrical conductivity. compacts were prepared by using the solid-state reaction method and sintered at 1500 °C for 6 h. The phase, analyzed from X-ray diffraction (XRD) patterns, changed from the single-phase cubic (0≤x≤0.12) to the mixture of cubic and hexagonal phases (0.12<x<0.20) and finally to the mixture of hexagonal and orthorhombic phases (0.2<x<1). Hexagonal and orthorhombic phases are dominant in 0.2≤x≤0.4 and 0.7≤x≤1.0, respectively. The diffraction peaks of two phases were overlapped and could not be easily separated, and the normalized unit cell volume seemed to change rapidly in 0.4<x<0.7, reflecting the change from the hexagonal-phase dominance to the orthorhombic-phase dominance. The electrical conductivity of (1−x)LSGM–xLSM, measured by four-probe d.c. method between 430 and 910 °C in air, decreased with increasing LSM content in the cubic composition range, showing the harmful effect of the LSM on the conductivity of the LSGM electrolyte. The conductivity decrease was explained by both the increase in the activation energy and the decrease in the charge carrier concentration. Above x=0.16, the conductivity increased rapidly, showing the effect of percolation by the conductive orthorhombic phase.