Impedance and admittance spectroscopy of Mn3O4-doped ZnO incorporated with Sb2O3 and Bi2O3

ZnO–Bi2O3–Sb2O3 (Sb/Bi=0.5) varistors were prepared with and without 1/3 mol% Mn3O4 along the conventional ceramic processing route. The bulk electron traps of ZnO were examined by admittance spectroscopy, and the respective electrical components such as resistance and capacitance of the specimens were determined by impedance–modulus spectroscopy. The bulk trap level of 0.25–0.32 eV in the depletion layer has been confirmed in all the specimens fired up to 1300 °C; those fired at 1300 °C, showed an additional trap level of 0.14 eV. It seems that the former represents VOradical dot and the latter represents Zniradical dotradical dot. In Mn-doped specimens, the bulk trap level of 0.33 eV and two interface states of 0.40 and 0.75–0.87 eV were confirmed by impedance–modulus spectroscopy. Among these, the interface trap level of 0.40 eV is thought to stem from the heterojunction of ZnO-intergranular phase modified by Mn.