In a randomly oriented polycrystalline ionically conducting material the total conductivity is reduced by the lengthening of the effective conduction pathway which is determined by the microstructure. It is, therefore, desirable to develop a better understanding of the relationship between the conductivity and the microstructure of the ceramic material.
This work focused on the quantification of the various contributions to the overall conductivity. Na-β” alumina ceramics with different microstructures but the same chemical composition were used as samples. Conductivity data were obtained by impedance spectroscopy measurements (IS) carried out in a temperature range from 350 to -30 °C at frequencies from 1 Hz to 500 KHz. An attempt has been made to calculate distinct geometric factors for the specific values of the grain and grain boundary contribution. These were inferred from the sample geometry, Laser Scanning Microscope (LSM) pictures, microstructural observations by image analysis, Transmission Electron Microscope (TEM) pictures, and considerations of the current pathways in the anisotropically conducting ceramic.