Electrical and dielectric properties of Mn-doped ZnO varistors

ZnO varistors have been extensively used against transient surges because of the excellent nonlinearity. ZnO varistors are obtained by sintering semiconducting ZnO powder with small amount of metal oxide additives. Amongst, Mn-doping is effective in the enhancement of the nonlinearity. In this paper, the relationship between the microstructure, the electrical and dielectric properties of Mn-doping ZnO-Bi
₂
O
₃
based varistors is investigated. The results show that with the increase of Mn-doping content, the grain growth is facilitated. Both the extrinsic and intrinsic defect relaxations can be adjusted by Mn additives. Mn-doping can improve the height of double Schottky barriers by enlarging the interface-state density of the depletion layer in the grain boundary. But too much Mn-doping can improve the concentration of intrinsic defects, resulting in the decrease of the barrier height.