Synthesis of Pr-doped ZnO nanoparticles by sol-gel method and varistor properties study

Pure and Pr-doped ZnO (0.5 at%, 1 at%,1.5 at% and 2 at%) nanoparticles are synthesized by sol-gel method and annealed at 500 °C for 2 h. The as-synthesized nanoparticles are characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) with energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The samples exhibited hexagonal ZnO lattice structure and another Pr6O11 phase was detected in the 2 at% Pr-doped ZnO nanoparticles. The calculated average crystalline size decreases from 29.73 nm to 25.5 nm when Pr content increased from 0 to 2 at%. The energy dispersive X-ray spectroscopy (EDS) analysis for 2 at% Pr-doped ZnO confirms the evidence of Pr in ZnO nanoparticles, and the varistor ceramics has a sintered density of 5.42 g/cm3 corresponding to 96.8% of its theoretical density, with breakdown voltage of 4380 V/cm and nonlinear coefficient of 16.5.