Effect of holding time on the dielectric properties and non-ohmic behavior of CaCu3Ti4O12 capacitor-varistors

Giant dielectric ceramics CaCu3Ti4O12 (CCTO) with non-ohmic electrical properties were prepared by a sol-gel processing method. Crystal structure and microstructure of the ceramics have been characterized using X-ray diffraction and Scanning electron microscopy. The effects of sintering duration and cooling rate on electrical properties of the ceramics were investigated by measuring the properties of permittivity, I-V and grain-boundary barriers. Prolonging holding time led to substantial improvement in permittivity, furthermore, the quenched sample showed larger dielectric permittivity than the furnace-cooling one. The non-ohmic behavior relating current density (J) to the applied electric field (E) at different temperatures was characterized. A low-voltage and giant dielectric permittivity CCTO varistor with breakdown voltages in the range of E (b) = 0.2-3 kV cm(-1), nonlinearity coefficient alpha = 2-6 and dielectric permittivity epsilon = 4,000-30,000 was obtained. A linear relationship between ln(J) and E (1/2) indicated that a Schottky barrier should exist at the grain boundary.