Mn Distribution in ZnO:Mn Ceramics: Influence of Sintering Process and Thermal Annealing

Manganese spatial distribution in ZnO:Mn ceramics (0.1–5 at.% Mn) sintered at 1100 °C in air has been investigated using Electron paramagnetic resonance (EPR), micro-Raman and Diffuse reflectance spectroscopy. The Raman and EPR spectra show that concentration of Mn incorporated in ZnO grains decreases from the surface of ceramic sample to its depth. Mn distribution in ZnO grains is also inhomogeneous. The concentration of Mn on Zn site centers (Mn Zn 2+ ) evaluated from the EPR data is found to be lower than the Mn content in the charge indicating a large amount of Mn remains in the intergranular spaces. Thermostimulated Mn redistribution between the ZnO grain and the intergranural spaces have been observed under post sintering annealing. The influence of ZnO native donors on Mn Zn 2+ center formation is found. It is supposed that this effect is due to interaction of Mn with interstitial zinc. The impact of native donor concentration on current-voltage characteristics of ZnO:Mn ceramics is demonstrated. The influence of Mn distribution on varistor characteristic is discussed.