Brick layer models (BLMs), although applicable at the microscale, are inappropriate for characterizing electroceramics at the nanoscale. A new construct, the nano‐grain composite model (n‐GCM), has been developed to model/analyze the AC‐impedance response of equiaxed polycrystalline electroceramics. The procedure employs a set of equations, based on the Maxwell–Wagner/Hashin–Shtrikman effective medium model, to calculate local electrical properties (conductivity, dielectric constant) for both “phases” (grain core, grain boundary) from experimental AC‐impedance spectra and also, for the first time, grain core volume fraction. The n‐GCM method was tested on a model system (a 3D‐BLM material) and demonstrated with a test case (nanograined yttria‐stabilized zirconia). The method appears to be applicable only at nanograin sizes, i.e., 10–100 nm. Limitations of the method, in terms of grain size (10–100 nm) and experimental uncertainty, are also discussed.

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In the microcrystalline regime, the electrical (impedance/dielectric) behavior of grain boundarycontrolled electroceramics is well described by the "brick-layer model" (BLM). In the nanocrystalline regime, however, grain boundary layers can represent a significant volume fraction of the overall microstructure. Simple boundary-layer models no longer adequately describe the electrical properties of nanocrystalline ceramics. The present work describes the development of a pixel-based finite-difference approach to treat a "nested-cube model" (NCM), which is used to investigate the validity of existing models for describing the electrical properties of polycrystalline ceramics over the entire range of grain core vs. grain boundary volume fractions, from the nanocrystalline regime to the microcrystalline regime. The NCM is shown to agree closely with the Maxwell-Wagner effective medium theory.

The reduction of grain size from the microcrystalline regime into the nanocrystalline regime is known to produce significant changes in the transport properties of polycrystalline ceramics. Part 1 of this series [1] described the development of a pixel-based finite-difference "nested-cube model" (NCM), which was used to evaluate existing composite models for the electrical/dielectric properties of polycrystalline ceramics over the entire range of grain core vs. grain boundary volume fractions, from the nanocrystalline regime to the microcrystalline regime. Part 2 addresses grain shape and periodicity effects in such composite modeling, and the extraction of local materials properties (conductivity, dielectric constant) from experimental impedance/dielectric spectroscopy data.

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