Effects of cooling rate on the microstructure and electrical properties of Dy2O3-doped ZnO-based var

The microstmcture,electrical properties,and density of Dy2O3-doped ZnO-based varistor ceramics,prepared using high-energy ball milling (HEBM) and sintered at 800℃,were investigated by increasing the cooling rate in the order of H (slow cooling in furnace) → L (cooling in furnace) → K (cooling in air).With the increase in cooling rate,the grain size and density decreased,the breakdown voltage (V1 mA/mm) increased, and the nonlinear coefficient (α) and leakage current (IL) exhibited extremum.The sample with the cooling type L showed the best properties with the breakdown voltage of 2650 V/mm, αof 20.3,IL of 5.2 μA,and density of 5.42 g/cm3.The barrier height (φB),donor concentration (Nd),density of the interface states (Ns),and barrier width (ω) all exhibited extremum during the alteration in cooling rate.The different relative amount of Bi-rich phase and its distribution as well as the characteristic parameters of grain boundary, resulting from the alteration of cooling rate,led to the changes in the properties of varistor ceramics.