The electrical properties of Mn3O4-doped ZnO

Polycrystalline ZnO doped with 1/3 mol% Mn3O4 was prepared by the conventional ceramic processing. From J–E characteristics the varistor behavior with nonlinear coefficient, α between 6 and 17 was confirmed in the Mn-doped ZnO sintered at 1000–1300 °C for 1 h in air, but was changed to ohmic behavior in the 1400 °C sintered specimen. In relation to the grain boundary resistivity, three activation energies of 0.37, 0.87 and 0.96 eV were detected from pre-breakdown J–E–T characteristic curves. The barrier height and donor concentration of the Mn-doped ZnO were calculated as about 1.0 V and 2×1017 cm−3 from C–V characteristics, respectively. Similar to commercial ZnO varistors, the deep bulk trap levels in Mn-doped ZnO were estimated as 0.13 and 0.25–0.32 eV by admittance spectroscopy. The varistor behavior of Mn-doped ZnO ceramics supports the formation of double Schottky type barrier in the grain boundary region. It is thought that the release and adsorption of oxygen on ZnO grain boundaries during the redox reaction of Mn ion is responsible for the varistor behavior of Mn-doped ZnO.