Abstract
We synthesize, for the first time, using sol-gel technique and without doping any trivalent impurities, monodispersed, spherical ZrO2 particles in size range of 500-600 nm, exhibiting metastable tetragonal crystal structure at room temperature. It is revealed using high-resolution transmission electron microscopy that "hard-aggregates" forming tendency of ZrO2 nanocrystallites of size 45 nm is responsible for stabilizing the high-temperature metastable tetragonal phase, at room temperature, within large sized (500-600 nm) undoped ZrO2 particles.