N. J. Kidner

Impedance/dielectric spectroscopy of electroceramics in the nanograin regime

ABSTRACT In the microcrystalline regime, the behavior of grain boundary-controlled electroceramics iswell described by the “brick layer model” (BLM). In the nanocrystalline regime, however, grainboundary layers can represent a significant volume fraction of the overall microstructure andsimple layer models are no longer valid. This work describes the development of a pixel-basedfinite-difference approach to treat a “nested cube model” (NCM), which more accuratelycalculates the current distribution in polycrystalline ceramics when grain core and grainboundary dimensions become comparable. Furthermore, the NCM approaches layer modelbehavior as the volume fraction of grain cores approaches unity (thin boundary layers) and itmatches standard effective medium treatments as the volume fraction of grain cores approacheszero. Therefore, the NCM can model electroceramic behavior at all grain sizes, from nanoscaleto microscale. It can also be modified to handle multi-layer grain boundaries and propertygradient effects (e.g., due to space charge regions).