Giant dielectric permittivity and non-linear electrical behavior in CaCu3Ti4O12 varistors from the molten-salt synthesized powder

CaCu3Ti4O12 (CCTO) powder has been prepared by a molten salt method using the NaCl–KCl mixture. Crystal structure and microstructure of the powder and the resulting ceramics have been characterized by using X-ray diffraction (XRD) and scanning electron microcopy (SEM). Impedance analyzer and current–voltage meter were employed to analyze dielectric and nonlinear (I–V) properties of the CCTO ceramics with different sintering durations and subsequent cooling rates. The values of dielectric permittivity and nonlinear coefficient of the quenched sample were found to be higher than those of the slowly cooled sample. More specifically, the cooling methods (quenching and furnace-cooling) have allowed to adjust; (і) the breakdown voltage within a rather low range of 0.3–4.4 kV cm−1; (іі) the nonlinear coefficient between 2 and 6 and (ііі) the giant dielectric permittivity for the ceramics within a range from 5000 to 20000. A double Schottky barrier can be evidenced from the linear behavior between the ln J and E1/2 in grain boundary regions. The relationship between the electrical current density and the applied electrical field indicates that the potential barrier height ΦB is holding time dependent.