Assessment of the electronic conductivity of core–shell, Fe-doped LSGM ceramics by impedance spectroscopy

The structure, microstructure and low-temperature electrical properties of core–shell-type mixed conductors based on lanthanum gallate with Fe-doped grain boundaries are analyzed in depth. Electron probe microanalysis revealed that the iron concentration in the grain-boundary regions (shell) is below 1 at.% and their thickness is no more than 1.5 μm. The low-temperature (< 400 °C) electronic conductivity is enhanced by up to 2–3 orders of magnitude with respect to the corresponding undoped ceramics, as revealed by the analysis of impedance spectra combined with microstructural information. The electronic transport numbers lie in the range between 0.35 and 0.1 at 275 to 400 °C, decreasing at higher temperatures, where the influence of grain boundaries on the overall transport properties vanishes and the ionic conductivity increases.