This paper deals with a perturbed angular correlation investigation of the microstructure and subsequent thermal evolution of a commercial ZrO2‐2. 8 mol% Y2O3 ceramic powder and of a pellet obtained upon sintering the powder at 1450°C. The perturbed angular correlation results, complemented by those of X‐ray diffraction and Raman spectrometry, indicate that the metastable tetragonal phase exhibits two hyperflne interaction forms instead of the interaction associated with the conventional t‐ZrO2 phase, both having different oxygen vacancy configurations around zirconium sites. While the powder sample exhibits mainly a very defective tetragonal form, the pellet exhibits a slightly distorted one as the major form. As temperature is increased, a reversible transformation between both forms occurs involving a redistribution of the oxygen vacancy. Once the transition is completed, the oxygen vacancy movement is described by a fast relaxation regime with an activation energy Eact= 0. 50 ± 0. 04 eV.
Tetragonal compact bodies obtained by quenching from the melt a ZrO 2 -2.8 mol% Y 2 O 3 commercial powder have been investigated between room temperature and 1150°C, using mainly perturbed angular correlations spectroscopy. The resulting nontransformable t phase observed by optical micrography is characterized at nanoscopic level by a hyperfine interaction describing defective and disordered Zr 4؉ neighborhoods very different from those of the regular tetragonal phase. A small amount of remaining Zr 4؉ sites corresponds to a scarcely distorted tetragonal structure. As the compacts are heated, two processes activate: the movement of vacancies and the gradual and irreversible conversion of t defective sites into less defective ones, probably resulting from oxygen absorption.
Two sol-gel derived zirconia powders were prepared at pH ס 0.5 and pH ס 5.5. They were investigated as a function of temperature using mainly perturbed angular correlation spectroscopy. The aim was to elucidate the relationship between the nanoscopic configurations around Zr 4+ ions and the morphology and structure of the powders. The highly porous material resulting from the solution at higher pH could be described mainly by defective and disordered, very hydrolyzed tetragonal arrays. As temperature increased, the amount of these arrays decreased while they became increasingly asymmetric, thus suggesting their superficial localization. The easy removal of hydroxyls led to the early appearance of the monoclinic phase. The gel obtained from the precursor at pH ס 0.5 was entirely described by configurations still involving organic residues. After their calcination, the powder underwent a well-defined two-step hydroxyl removal thermal process leading to the crystallization of the tetragonal and the monoclinic phases. The thermal stability of the metastable tetragonal phase in the investigated powders seems to be controlled by their different capability to absorb oxygen.
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