IMPEDANCE SPECTROSCOPY OF SUPERIONIC CONDUCTORS II: MEASUREMENT AND STUDIES

Abstract

Ionic conducting materials are increasingly playing a crucial role in the search for complimentary sources of energy. They are used in rechargeable batteries for mobile phones and laptop computers for example. However, the most important application of these materials is in the current search for solid oxide fuel cells (SOFC) desperately needed in the transportation sector. The main advantage of these materials as energy storage devices are their being in the solid state, offering portability and flexibility in handling, compared to the traditional liquid electrolytes. Their electrical conductivity at room temperature is comparable to those of the liquid ones. Among the class of ionic materials are the Superionic conductors that have the best conductivity at elevated temperatures or room temperatures. The ultimate challenge in their study is to reduce the temperature to ambient conditions. Various methods have been adopted to achieve this, one of which is by modifications in the stoichiometric compositions of the system or substitution in order to tailor them for targeted applications. One such class of materials is called NASICON, which is sodium Superionic conductor. These compounds have conductivities comparable to the best superionic conductors due to their special structures and wide range of applications, hence the interest in their research. However, the conductivity and impedance spectroscopy of these materials presents challenges from theoretical interpretation of the results. This review therefore briefly explores the impedance spectroscopy results for some NASICON materials in relation to their synthesis conditions.Their general properties have also been presented.