Synthesis and Characterization of ZnO/Bi2O3 Core/Shell Nanoparticles by the Sol-Gel Method

In this work, a novel two-step synthesis of ZnO/Bi2O3 core/shell nanoparticles is presented. Spherical core particles of ZnO were first synthesized by a 95 degrees C direct precipitation method with the assistance of polyethylene glycol (PEG-6000) surfactants, and then used as precursors to prepare ZnO/Bi2O3 core/shell particles via a 70 degrees C low-temperature sol-gel method. Techniques including x-ray diffraction, Fourier-transform infrared spectroscopy, transmission electron microscopy, energy-dispersive x-ray spectroscopy and scanning electron microscopy were employed to characterize the as-synthesized samples. The ZnO nanoparticles were almost spherical in shape, with particle size ranging from 15 nm to 28 nm, and belonged to a hexagonal wurtzite crystal structure. Furthermore, the experimental result showed that ZnO nanoparticles were fully covered with Bi2O3. In addition, using ZnO/Bi2O3 core/shell nanoparticles (1 mol.% Bi2O3) via this sol-gel method, after sintering in air at 1100 degrees C for 2 h, the varistors showed maximum relative density of 96.6%, with high breakdown voltage (2191 +/- 0.72 V/cm), low leakage current (0.12 +/- 0.07 mu A) and nonlinear coefficient (6 +/- 0.14), suggesting that nano-coating is a promising route for the preparation of ZnO varistors.