ZnO nanopowders doped with bismuth oxide, from synthesis to electrical application

Abstract Bismuth doped ZnO nanopowders with doping concentrations between 0 and 7 %mol were successfully synthesized with a soft chemistry method: the sol-gel route. This method allows obtaining powders with a good quality in a nanometric size range. The well-defined optimal conditions for the synthesized powders are given. The hydrated zinc acetate dissolved in ethylene glycol is used as a precursor for the zinc oxide (ZnO), with different small amount of Bi concentrations (1%, 3%, 5% and 7%). After calcination at 500 °C, the powders are consolidated into pellets and sintered using a conventional furnace and then characterized by: X-ray diffraction, SEM, TEM, and J(E) electrical measurements. Finally, the obtained material has been used to prepare varistors. The XRD patterns indicate that pure and Bi doped ZnO are solid solutions with average grain sizes varying between 65 nm and 48 nm. The β-Bi 2 O 3 liquid phase of tetragonal structures appears as a secondary phase for a 5% mol concentration of Bi. High-resolution TEM images of Bi doped ZnO particles indicate that during the sintering of Bi-doped ZnO, the growth of particles leads to a change in the microstructure of ZnO giving semi-transparent cylindrical nanotubes. J(E) results indicate that the content of Bi increases the nonlinearity coefficient α and the breakdown fields V B of the binary Zn %Bi-O varistors. The 7% doped Bi-ZnO varistor gives the best electrical characteristics for varistors.