Modeling the electrical (impedance/dielectric) behavior of nanocrystalline and thin film electroceramics

The electrical (impedance/dielectric) behavior of two emerging electroceramic systems: thin film and nanocrystalline electroceramics were investigated using a pixel-based, finite-difference numerical program. Frameworks were constructed that enable the local electrical properties to be determined through analysis with impedance/dielectric spectroscopy (I/DS).; A numerical 'nested-cube model' (NCM) was developed to assess the validity of existing microstructural models to describe the impedance/dielectric behavior of polycrystalline electroceramics. Only the NCM and an effective media model, termed the Maxwell-Wagner Hashin-Shtrikman (MWHS) model were found to accurately describe the electrical properties over the entire range of grain core vs. grain boundary volume fractions, from the microcrystalline regime to the nanocrystalline regime. Based on grain morphology and intrinsic conductivity arguments the difference between these models led to a procedure to extract the local electrical properties from experimental I/DS data of isotropic, polycrystalline ceramics.; The numerical model was modified to investigate the use of co-planar interdigital electrode (IDE) structures to characterize the electrical properties of electroceramic thin films. A periodic, two-dimensional IDE structure was simulated to study different electrode geometries and film thicknesses. The results of capacitance simulations led to modification of an existing semi-empirical equation to improve the characterization of the dielectric properties of thin films. Subsequent resistance simulations extended the analysis to relate the conductivity of the film to the measured resistance.; Variable-frequency simulations showed that the film/IDE system can be modeled as a parallel resistor-capacitor, RC, equivalent circuit. Equations were developed to extract from the equivalent circuit's fitted resistance and capacitance, the electrical properties of the thin film, both conductivity and permittivity. The electrical properties of a poly-domain barium titanate film grown on a magnesium oxide substrate were measured with an IDE structure by I/DS to demonstrate how the methodology can be applied.; Simulations investigated how anisotropy affects the I/DS behavior of both nanocrystalline electroceramics (anisotropic grain boundary properties) and thin film electroceramics (anisotropic film properties). The successfully incorporation of anisotropy into the I/D analysis indicates that with suitable care, the I/DS behavior of complicated systems can be characterized.