Abstract
Cation tracer diffusion of 138La, 84Sr and 25Mg in polycrystalline samples of doped lanthanum gallate, La0.9Sr0.1Ga0.9Mg0.1O2.9, was investigated by SIMS for temperatures between 900 °C and 1400 °C. It was found that diffusion takes place through the bulk and along the grain boundaries. The bulk diffusion coefficients are similar for all cations with activation energies which are strongly dependent on temperature. At high temperatures, the activation energies are about 4.5 eV, while at low temperatures values of about 1.5 eV are found. These results are explained by a frozen in defect structure at low temperatures. This means that the observed activation energy at low temperatures represents only the migration energy of the different cations while the observed activation energy at high temperatures is the sum of the defect formation energy and the migration energy. The migration energies of all cations are nearly identical, although 138La and 84Sr are occupying A-sites while 25Mg is occupying B-sites in the perovskite-structure. To explain these experimental findings we propose a defect cluster containing cation vacancies of both the A- and the B-sublattice and anion vacancies as well.
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