Synthesis of ZnO@Co2O3-Bi2O3-MnO core-shell structured nanoparticles for varistors applications

In this paper, ZnO@Co2O3-Bi2O3-MnO nanocomposites with a homogeneous core–shell nanostructure have been synthesized by encapsulating Co2O3-Bi2O3-MnO on the surfaces of the as-prepared ZnO nanoparticles via an in situ precipitation method. Techniques of XRD, TEM, SEM and EDS have been employed to characterize the as-synthesized nanopowders and varistor samples. The results showed that ZnO nanoparticles were fully covered with additional metal oxides and Bi12Mn0.5Co0.5O20 phase was observed at the as-prepared ZnO nanopowders after calcined at 700 °C. The varistor ceramics sintered at 1100 °C for 2 h in air have a density of 5.56 g/cm3 corresponding to 96.2% of the theoretical density, with breakdown voltage of 3285 V/cm and nonlinear coefficient of ~ 5.5.