The specific grain interior and grain boundary conductivities, obtained from impedance spectroscopy and the brick layer model, are reported for BaZr 0.9 Y 0.1 O 3 − δ as a function of p O 2 and temperature. p O 2-dependencies were indicative of dominating ionic and p-type electronic conduction for the grain interior under reducing and oxidizing conditions, respectively, while the grain boundaries showed an additional n-type electronic contribution under reducing conditions. Transmission electron microscopy revealed enrichment of Y in the grain boundary region. These findings indicate the existence of space-charge layers in the grain boundaries. A grain boundary core-space-charge layer model is therefore applied to interpret the data. Using a Mott-Schottky approximation, a Schottky barrier height of 0.5-0.6 V and an effective grain boundary width of 8-10 nm (= 2× space-charge layer thickness) is obtained at 250°C in wet oxygen. Finite-element modelling of the complex impedance over a grain boundary with a space-charge layer depletion of protons yields a distorted semicircle as observed in the impedance spectra.

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