Role of Bismuth Doping on Structural and Electrical Properties of ZnO Nanocrystals Prepared by Sol–Gel Method

This study deals with the effects of Bi doping on the structural, optical, dielectric, and electrical properties for ZnO nanoparticles synthesized by the sol–gel method. X-ray diffraction measurements revealed that all samples crystallized with a hexagonal wurtzite structure, and, as the Bi concentration increased from 0 mol% to 7 mol%, the crystallite size increased from 36.10 nm to 47.78 nm. Scanning electron microscopy observation showed that the morphology of ZnO particles is affected by the Bi doping concentration, forming spherical and rod-shaped particles. The optical band gap for the samples determined by UV–Visible spectra gradually decreased from 3.257 eV to 3.065 eV with the Bi content increasing. Impedance analysis showed only one semicircle in all the samples, indicating that the contribution of grain boundaries is greater than that of the grains. The dielectric properties of ZnO were improved by doping Bi, the dielectric loss was significantly reduced from 10.4 to 0.2, and the dielectric constant stabilized at around 180 in the high-frequency region. It was also found that the conductivity was improved by doping Bi, with the highest conductivity corresponding to the 5% Bi content. Additionally, the 5% Bi-doped ZnO has the best dielectric properties, with a dielectric constant of 180 and a dielectric loss lower than 0.2 within the temperature range of 100–200°C at an operating frequency of 1 MHz. These results suggest that Bi-doped ZnO nanocrystals may be promising candidates for dielectric applications.