Abstract
Oxygen exchange with the ambient atmosphere and oxygen diffusion are assumed to play a decisive role in the re-oxidation process of positive temperature coefficient (PTC) resistors based on donor doped barium titanate. 18O tracer experiments with subsequent time-of-flight secondary ion mass spectrometry (ToF-SIMS) measurements were thus carried out to investigate the oxygen diffusion properties of donor doped barium titanate. Fast grain boundary diffusion was found at temperatures between 750 °C and 900 °C. Moreover, evidence is given for a position dependent diffusion coefficient close to the surface. The secondary phase developing during the production process is shown to be Ti-rich and hardly any oxygen tracer exchange with this secondary phase could be observed. This suggests that grain boundary diffusion does not take place via such secondary phases. Rather, evidence of diffusion along an oxygen vacancy enriched space charge region is found.
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