The Brick Layer Model Revisited: Introducing the Nano-Grain Composite Model

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.