Effects of cooling rate on the microstructure and electrical properties of Dy 2O 3-doped ZnO-based varistor ceramics

Abstract

Abstract The microstructure, electrical properties, and density of Dy 2O 3-doped ZnO-based varistor ceramics, prepared using high-energy ball milling (HEBM) and sintered at 800°C, 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 ( V 1 mA/mm) increased, and the nonlinear coefficient (α) and leakage current ( I L) exhibited extremum. The sample with the cooling type L showed the best properties with the breakdown voltage of 2650 V/mm, α of 20.3, I L of 5.2 μA, and density of 5.42 g/cm 3. The barrier height (Ø B), donor concentration ( N d), density of the interface states ( N s), 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.