Abstract
AbstractVaporization 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 coefficientsDGaand vaporization coefficients αGawere 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 of139La,84Sr and25Mg as well as cation impurity diffusion of144Nd,89Y and56Fe in polycrystalline samples of doped lanthanum gallate were directly determined for the composition La0.9Sr0.1Ga0.9Mg0.1O2.9as 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 ABO3perovskite lattice and by proposing a defect cluster containing cation vacancies in the A and B sublattices, as well as oxygen vacancies.
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