Novel route for preparation of high voltage varistor powder

A novel technique for preparing ZnO varistor powder is described. It involves preparation of gel by adding citric acid to nitrate solution of varistor constituents. The gel on subsequent calcination forms submicron reactive varistor powder that exhibits the homogeneity and stoichiometric control associated with the chemical methods of preparation. SEM and BET surface area measurements show the resultant powder to comprise crystallite of submicron size. High field varistors with good nonlinear coefficient result from sintering at 1150 °C for 1 hour. The high value of nonlinear coefficient of the varistor sample can be attributed to the more uniform distribution of dopants and formation of more varistor active grain boundaries. The electrical characteristics of the citrate gel derived varistor are compared to those of a varistor sample prepared through the urea route.