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Vaporization and Diffusion Studies on the Stability of Doped Lanthanum Gallates
Author(s) -
Stanislowski M.,
Peck D.H.,
Woo S.K.,
Singheiser L.,
Hilpert K.,
Schulz O.,
Martin M.
Publication year - 2006
Publication title -
fuel cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.485
H-Index - 69
eISSN - 1615-6854
pISSN - 1615-6846
DOI - 10.1002/fuce.200500232
Subject(s) - vaporization , diffusion , lanthanum , doping , analytical chemistry (journal) , chemistry , crystallite , grain boundary diffusion coefficient , impurity , materials science , grain boundary , thermodynamics , inorganic chemistry , crystallography , microstructure , chromatography , physics , optoelectronics , organic chemistry
Vaporization and diffusion determine the stability of doped lanthanum gallates under SOFC operating conditions. Systematic vaporization studies of Ga and other elements were carried out using the vapor transpiration method. It was shown that the Ga vaporization is controlled by diffusion from the bulk to the surface. Diffusion coefficients D Ga and vaporization coefficients α Ga were determined by fitting the measured vaporization data to a vaporization model. Secondary phases formed as a result of the vaporization were detected. The influence of different doping levels of Sr, Mg and Fe on the Ga vaporization was elucidated. Moreover, cation self‐diffusion of 139 La, 84 Sr and 25 Mg as well as cation impurity diffusion of 144 Nd, 89 Y and 56 Fe in polycrystalline samples of doped lanthanum gallate were directly determined for the composition La 0.9 Sr 0.1 Ga 0.9 Mg 0.1 O 2.9 as an example, from diffusion profiles determined by SIMS. It was found that diffusion occurs by means of bulk and grain boundaries. The bulk diffusion coefficients are similar for all cations with activation energies which are strongly dependent on temperature. The results are explained by a frozen‐in defect structure at low temperatures in the ABO 3 perovskite lattice and by proposing a defect cluster containing cation vacancies in the A and B sublattices, as well as oxygen vacancies.