Molten salt synthesis of doped nanocrystalline ZnO powders and applications in varistor ceramics

摘要

The doped nanocrystalline ZnO powders were synthesized with the aid of NaNO_3-KNO_3 eutectic instead of any organic additives. The as-synthesized samples were characterized by X-ray diffraction, transmission electron microscopy, inductively coupled plasma-atomic emission spectrometry, X-ray fluorescence, electronic differential system and scanning electron microscopy. Spherical doped nanocrystalline ZnO powders with particle size of about 20-37 nm were easily obtained in the presence of NaNO_3-KNO_3 eutectic. The results indicated that NaNO_3-KNO_3 eutectic, which acted as solvent as medium, was in favor of the formation of well-dispersed doped ZnO nanocrystals. The ZnO varistor sintered at 1100 ℃ for 2 h in air have a density of 5.43 g/cm~3 corresponding to 96.9 % of its theoretical density, with breakdown voltage of 5893 V/cm and nonlinear coefficient of 26.6. The experimental results showed the advantage of addition of the molten salt for avoiding hard agglomeration and improving electrical performance of the varistors.