Additives distribution and electrical properties in zinc oxide varistor prepared by a wet chemical method

Cobalt-, praseodymium-added zinc oxide varistor was prepared through a wet chemical method followed by sintering with or without calcination. Changes in grain size, compact density, additives distribution, and voltage-current/capacitance-voltage relations were investigated for the characterization of the samples sintered at temperatures from 1473 to 1573 K without calcination or with calcination al 773 K for 2 h. The electrical properties were compared with those of samples prepared by two types of ball mill methods. The wet chemical method provided almost the same additives-distribution profile and less impurities in comparison with the ball grinding method carried out for 10-100 h. The donor concentration and the potential-barrier height for the samples were evaluated by Double Schottky Barrier Model. Addition of small amount of both cobalt and praseodymium in preparation by the wet chemical method was effective for a better nonlinearity relation between voltage and current, which has potential for a smaller sized varistor.