Résumé:
The goal of this thesis is to realize zinc oxide (ZnO) varistors doped with cobalt (Co)
from nanosized powders, in order to explore the relationship between the reduction in particle size and the varistor effect. To do this, nano-powders of pure ZnO and doped with cobalt (Co) have been prepared by soft chemistry method known by the name of Sol-Gel. The structural and morphological characterizations were obtained through XRD spectra and Fourier Transform Infrared Spectroscopy (FTIR) and scanning electron microscopy (SEM). XRD results indicate that the powders obtained from the two types of precursors have a hexagonal structure « würtzite », a size of nano-particles without any new phase for either pure ZnO or Zn-C-x% O. A decrease in particle size by increasing the Co content up to 7% is however to be noted. The results obtained from the XRD characterization are confirmed by the (FTIR) analysis.The study of various varistors by microwave sintering, showed: a homogeneous distribution of grains as observed by SEM and a density reaching 93% in spite of the very short sintering duration.Electrical characterization I (V) of these ceramics shows a marked non-linear behavior in the sintering temperature range 1000 °C and 1075 °C, resulting in an improvement of the coefficient α and the outbreak field, which increased significantly with the decrease in grain size.The obtained results encourage the use of this model of nanostructured varistors for applications in microelectronics.
