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Thermodynamic and Cation Diffusion Studies of Perovskites on the Basis of LaGaO 3 and Implications for SOFC
Author(s) -
Matraszek A.,
Kobertz D.,
Singheiser L.,
Hilpert K.,
KuncewiczKupczyk W.,
Miller M.,
Schulz O.,
Martin M.
Publication year - 2002
Publication title -
materialwissenschaft und werkstofftechnik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.285
H-Index - 38
eISSN - 1521-4052
pISSN - 0933-5137
DOI - 10.1002/1521-4052(200206)33:6<355::aid-mawe355>3.0.co;2-g
Subject(s) - vaporization , perovskite (structure) , electron microprobe , analytical chemistry (journal) , diffusion , chemistry , thermodynamics , phase (matter) , electrolyte , mineralogy , crystallography , physics , organic chemistry , electrode , chromatography
Solid phase equilibria in the quasi quaternary system La 2 O 3 ‐Ga 2 O 3 ‐SrO‐MgO near the solubility lobe of the (La,Sr)(Ga,Mg)O 3−δ perovskite phase were determined by XRD, SEM/EDX and EPMA of annealed and quenched samples. Equilibration of the samples during these measurements was ensured by considering diffusion of the cations which are the slowest moving species and determine all equilibration processes. Vaporization studies of the perovskite phase La 1− x Sr x Ga 1− y Mg y O 3−( x+y )/2 and of the Ga 2 O 3 ‐La 2 O 3 system were carried out by the use of Knudsen effusion mass spectrometry in the temperature range between 1600 K and 1900 K. The gaseous species O 2 , Ga, GaO, Ga 2 O, and LaO, as well as in part also Mg, Sr and SrO were detected over the samples investigated. Thermodynamic activities and Gibbs energies of formation of the quasi binary compounds LaGaO 3 (s) and La 4 Ga 2 O 9 (s) resulted from the measurements. The data obtained are used to compute the vaporization of La 0.90 Sr 0.10 Ga 0.80 Mg 0.20 O 2.85 being considered as SOFC electrolyte by thermodynamic modeling for different SOFC operating conditions. A high volatility results for the anode side. Diffusion of the impurities Y, Fe and Cr was investigated by SIMS at 1673 K for different compositions of symmetrically doped LSGM, La 1− x Sr x Ga 1− x Mg x O 3− x ( x = 0.0, 0.02, 0.10, 0.20) showing that diffusion occurs via bulk and grain boundaries. Implications for the kinetic stability of LSGM in a SOFC are discussed.