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Medientyp:
E-Artikel
Titel:
Blocking Grain Boundaries in Yttria‐Doped and Undoped Ceria Ceramics of High Purity
Beteiligte:
Guo, Xin;
Sigle, Wilfried;
Maier, Joachim
Erschienen:
Wiley, 2003
Erschienen in:Journal of the American Ceramic Society
Sprache:
Englisch
DOI:
10.1111/j.1151-2916.2003.tb03281.x
ISSN:
0002-7820;
1551-2916
Entstehung:
Anmerkungen:
Beschreibung:
<jats:p>CeO<jats:sub>2</jats:sub> samples doped with 10, 1.0, and 0.1 mol% Y<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> and undoped CeO<jats:sub>2</jats:sub> samples of high purity were studied by impedance spectroscopy at temperatures <800°C and under various oxygen partial pressures. According to microstructural investigations by SEM and analytical STEM (equipped with EDXS), the grain boundaries were free of any second phase, providing direct grain‐to‐grain contacts. An amorphous siliceous phase was detected at only a few triple junctions, if at all; as a result, its contribution to the grain‐boundary resistance was negligible. Nevertheless, the specific grain‐boundary conductivities were still 2–7 orders of magnitude lower than the bulk conductivities, depending on dopant concentration, temperature, and oxygen partial pressure. The charge carrier transport across the grain boundaries occurred only through the grain‐to‐grain contacts, whose properties were then determined by the space‐charge layer. The space‐charge potential in acceptor‐doped CeO<jats:sub>2</jats:sub> was positive, causing the simultaneous depletion of oxygen vacancies and accumulation of electrons in the space‐charge layer. The very low grain‐boundary conductivities can be accounted for by the oxygen‐vacancy depletion; the accumulation of electrons became evident in weakly doped and undoped CeO<jats:sub>2</jats:sub> at high temperatures and under low oxygen partial pressures.</jats:p>