Fine representation of dielectric properties by impedance spectroscopy

Abstract

Dielectric spectroscopy is used as a quick, precise and nondestructive examination tool of macroscopical dielectric properties for dielectrics. However, if the information of the microstructure and the location of a certain dielectric relaxation can be learned also by dielectric spectroscopy, it will help to reveal point defect structure and macroscopic and microscopic mechanisms of conduction and dielectric relaxation. Fine representation of dielectric properties by impedance spectroscopy (IS) is analyzed carefully in this paper. It is found that IS is not a good tool to describe a uniform system because a pseudo relaxation peaks exists at low frequency limit corresponding to direct current (DC) conductivity, and two relaxation peaks appears simultaneously corresponding to only one relaxation process for a high loss system with tanδ>1. However it is very convenient to describe a multiple phase system with IS for that only one Cole-Cole arc with some distortion appears for every phase with several relaxations, therefore it is very easy to distinguish different phases from each other. Especially, the location of a true relaxation process can be deduced by IS without any uncertainly according to pseudo relaxation theory which is built in this paper. Furthermore, when dielectric properties are shown with specific impedance spectroscopy (SIS), the information of the microstructure can be obtained conveniently. Based on these theoretical results above, dielectric properties of CaCu3Ti4O12 (CCTO) ceramics with giant dielectric constant (GDC) are investigated. It is found that GDC comes from pseudo relaxation of grain.