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 α = 2–6 and dielectric permittivity ε = 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.