Perturbed-Angular-Correlation Study of Zirconias Produced by the Sol-Gel Method

Zirconia powders, prepared by a sol-gel method using zirconium n -propoxide (ZNP) and different H₂O/ZNP and alcohol/ZNP ratios, were investigated by the perturbed-angular-correlation method, along with X-ray diffraction (XRD), Raman spectroscopy, differential thermal analysis (DTA), and thermogravimetric analysis (TGA) techniques. The hyperfine interaction was measured after annealing the samples at increasing temperatures up to 1080°C. Two disordered structures, giving tetragonal patterns in XRD and Raman analysis, were identified in as-produced powders, which consisted of chains of fully hydrolyzed species and chains containing residual organic groups. As the annealing temperature was increased, crystallization occurred, producing the tetragonal and monoclinic phases of zirconia. All powders were essentially monoclinic at the highest temperatures. Those representing low H₂O/ZNP ratios retained a large amount of tetragonal phase over a wide temperature range and transformed to monoclinic with a higher activation energy.