Effect of Mn doping on electrical properties and accelerated ageing behaviours of ternary ZVM varistors

Abstract

The electrical properties and d.c. accelerated ageing behaviour of ZVM (Zn-V-Mn) ceramics were investigated with different valences and contents of Mn. The incorporation of Mn into the ZV ceramics was found to restrict the abnormal grain growth of ZnO. The nonlinear properties and stability against the d.c. accelerated ageing stress are significantly affected by different valences and contents of Mn. The high valence of Mn (Mn⁴⁺) in the ZVM ceramics resulted in better nonlinear properties than low valence of Mn (Mn^2·66+). Furthermore, an increase in doping level of MnO² greatly improved its nonlinear properties. The ZVM ceramics doped with 2 mol% MnO² exhibited not only a high nonlinearity, in which the nonlinear coefficient is 27 and the leakage current density is 0·042 mA/cm², but also a good stability, in which %ΔE _{1 mA} = −2·1%, %Δα = −25·9% for the d.c. accelerated ageing stress of 0·85 E _{1 mA}/85°C/24 h.