Abstract: Kinds and causes of deep electron traps in the depletion region of ZnO varistors and effects of some additives on the traps have been studied by using admittance spectroscopy method. The results show that some additives such as Ba have a restraint effect on the formation of intrinsic defect Zn_i²⁺. The detection of Zn_i²⁺ depends not only on the defect density, but also on the measurement temperature. Besides the normal conductance peaks 1 and 2, that are considered to associate with the intrinsic defects Vo⁺ and Zn_i²⁺, peak 3 has been observed at lowwtemperature (about -170℃) and the corresponding trapping level is E_t=0. 163eV, the capture cross section is σ_n=7.71×10^-12cm² and the room temperature (300K) thermal emission time constant is τ=1. 11×10^-6μs.The conductance peak might be caused by extrinsic defects resulting from the interaction between grain boundary and the additives.

Key words: adddmittance spectroscopy, extrinsic defect, ZnO varistor ceramics, intrinsic defect