Thermionic insulator testing (AC impedance spectroscopy)

The feasibility of applying AC impedance spectroscopy, a potentially useful characterization technique for insulators, to the highly resistive materials of interest for use in thermionic power conversion systems was studied. All samples of dense and porous yttria and YAG tested exhibited two semicircular loops indicative of lumped R-C behavior. The two semicircles were interpreted as bulk and grain boundary subcircuits. The equivalent circuit parameters and activation energy of conduction for each specimen type were calculated and tabulated. These parameter can be used to characterize the test materials. The results of the study confirm the usefulness of AC impedance spectroscopy