Application of Impedance Spectroscopy to Materials Science

Abstract

In this article the term spectroscopy is used to describe any technique in which data, equivalent to the real and imaginary parts of a complex electrical quantity, are measured as a function of frequency. The frequency range involved here is from about 1 04 to about 106 Hz. The complex electrical quantity may be impedance, conductance, permittivity, electric modulus, etc . Although the most widely used data acquisition technique is single-point detection in the frequency domain, measurement methods based on injection of multiple frequencies, Fourier trans­ formation from the time domain, and analysis of noise spectra are not excluded. The results, however, will always be presented and discussed in the frequency domain. In recent years, acquisition of impedance spectra has been dramatically simplified, first by automatic phase-sensitive detectors, and second by direct digital sampling of signals . For the deter­ mination of bulk properties, such as ionic conductivity, two point measure­ ments are adequate; but for s tudies of interfacial phenomena three elec­ trode measurements are usually made, often via a potentiostat, which allows the de bias at the electrode/electrolyte interface to be independently varied. Depending on the relative values of the sample and lead impedances compared with the input impedance of the measuring system, varymg amounts of care may have to be taken to avoid spurious effects.