Sintering behavior of Zn–Pr–Co–Mn–O varistor ceramics

Sintering and grain growth of Pr6O11-based ZnO varistors were investigated in detail over a range of temperature and holding time. The grain growth kinetics in the Zn–Pr–Co–Mn–O system was studied using the simplified phenomenological grain growth kinetics equation: image = K0 t exp (−Q/RT) together with the physical properties of the sintered samples. From 1050 °C to 1300 °C, the grain growth exponent value (n) and the apparent activation energy for this system were found to be approximately 3.7 and 306 ± 61 kJ/mol respectively. Highly densified ceramics sintered at 1300 °C for 4 h were obtained, reaching about 96% of theoretical density (TD = 5.78 g/cm3). These values are compared with those obtained for Bi2O3-based ZnO varistors. The maximum nonlinear exponent (α = 54.7) was obtained at a sintering temperature of 1275 °C.