ZrO2 Nanoparticles Synthesized by the Sol–Gel Method: Dependence of Size on pH and Annealing Temperature

Abstract

Zirconium oxide(ZrO₂) is an important ceramic material characterized by a wide optical bandgap, low optical losses, high dielectric constant, excellent physical and structural properties, high coefficient of thermal expansion and chemical stability. This paper reports the synthesis of ZrO₂ nanoparticles by the sol–gel method using ZrO(NO₃)₂ as the zirconium precursor and ammonia solution (25%) as the precipitating agent. The pH value of the sol and the annealing temperature strongly influence the morphology and size of nanoparticles. In the present work, the sol pH was varied from 8 to 11 and the nanoparticles obtained were annealed in the temperature range of 400–700°C. The structural, morphological and optical properties of the nanoparticles were investigated using x-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and photoluminescence measurements. The results demonstrate that the stable t-ZrO₂ phase starts appearing above 400°C, with nanoparticle size varying in the range of 15–22 nm. The optimal size of ZrO₂ nanoparticles (15.65 nm) was obtained at a pH value of 9 and an annealing temperature of 500°C.