Abstract
The effects of different synthesis routes and sintering temperatures on the microstructures and electrical properties of ceramic varistors (composed of ZnO doped with Pr
6
O
11
, Co
3
O
4
, Cr
2
O
3
, and Nd
2
O
3
) were investigated. Two types of samples were prepared according to the milling approach (single-mill or double-mill). Remilling the calcined powder material reduced the required sintering temperature by 100 °C, improved the microstructure of the ceramic, and enhanced the nonlinear properties of the varistor. Though the different sintering temperatures and average grain sizes, both types were reach ≈ 98% of the theoretical density. The highest nonlinear coefficient value was ≈ 26.5, obtained from the first sample of the double-mill batch. As the sintering temperature increased, the nonlinearity diminished rapidly in the case of single-mill samples compared to double-mill ones. Similar behavior was noted for the varistor (breakdown) voltage. The thermionic emission behavior at the pre-breakdown region and the conduction mechanism through Schottky barriers were applied to find further electrical parameters.