Cation Self and Impurity Diffusion in Polycrystalline La0.9Sr0.1Ga0.9Mg0.1O2.9

Abstract

Cation self-diffusion of 139 La, 84 Sr and 25 Mg and cation impurity diffusion of 144 Nd, 89 Y and 56 Fe in polycrystalline samples of doped lanthanum gallate, La 0.9 Sr 0.1 Ga 0.9 Mg 0.1 O 2.9 , was investigated by SIMS for temperatures between 900°C and 1400°C. 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. At high temperatures, the activation energies are about 5 eV, while at low temperatures values of about 2 eV are found. These results are explained by a frozen 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 for all cations are nearly identical, although 139 La, 84 Sr and 144 Nd are occupying A-sites while 25 Mg and 36 Fe are 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.