New insight into the colossal dielectric constant of polycrystalline CaCu3Ti4O12 underlying the physical mechanisms of the dielectric relaxation

Abstract

The new mechanisms of dielectric relaxations previously proposed for polycrystalline CaCu3Ti4O12 (CCTO), modeled by the super-linear power law and extended power law concerning the AC conductivity spectra, are presented on the basis of the cluster model and percolation theory. The relaxations are determined by the cluster size or correlation length, varying with frequency. The occurrence of quasi-plateau relaxation in the low-frequency regions is attributed to the cluster size approximating the percolation size because the occupation fraction or probability approaches the percolation threshold. The physical significance of the independent term (σ0) in Jonscher’s power law is discussed and redefined. The proposed new mechanisms concerning the dielectric relaxations manifest the comprehensive mechanism concerning the development of the colossal permittivity, lend support to the validity of the extended power law, and provide new insight into the calculation of the activation energy of each relaxation in the AC conductivity spectra of polycrystalline CCTO.