ZnO nanoparticles of different particle sizes were synthesized via the hydrothermal method by varying the
autoclave reaction temperature from 100 ◦C to 200 ◦C. The shape and particle size of the produced ZnO
nanoparticles were investigated by X-ray diffraction (XRD), UV–visible spectrophotometer, scanning electron
microscopy (SEM), transmission electron microscope (TEM), and laser-induced breakdown spectroscopy technique
(LIBS). These studies showed that the prepared samples had high purity crystalline structure with wurtzite
hexagonal ZnO and its crystallinity increases as the reaction temperature increases. Its absorption spectrum
showed that the maximum absorption intensity was shifted to a higher wavelength, followed by increasing their
particle sizes as the reaction temperature increases. Its morphological images showed increases in roughness and
decreases in particle sizes as the reaction temperature increases. The intensity of the characteristic Zn peak of
LIBS spectrum was decreased due to increasing of their particle size as the reaction temperature increases.
Finally, the dielectric behavior of the prepared samples was studied revealing the dependence on their particle
sizes.