Phase characterization and electrical conductivity of LaSr(GaMg)(1-x)MnxO3 system

Abstract

LSGM (La0.9Sr0.1Ga0.8Mg0.8Mg0.2O3) 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-x)MnxO3 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. Powder compacts were prepared by using the solid-state reaction method and sintered at 1500 degreesC for 6 h. The phase, analyzed from X-ray diffraction (XRD) patterns, changed from the single-phase cubic (0 less than or equal to x less than or equal to 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 0.2less than or equal toxless than or equal to0.4 and 0.7less than or equal toxless than or equal to1.0, 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 chan-e 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 9 10 degreesC 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. (C) 2002 Elsevier Science B.V. All rights reserved.