Influence of synthesis conditions on the crystal structure of the powder formed in the ZrO₂ - Ce₂O₃/CeO₂ system.

Influence of synthesis conditions (type of atmosphere, reduction and oxidation, annealing temperature) on the chemical composition and structure of the compounds formed in the "ZrO₂ - Ce₂O₃ / CeO₂" system has been investigated by X-ray absorption fine structure (XAFS) spectroscopy combined with X-ray diffraction (XRD) and thermogravimetric analysis (TGA). It is revealed that isothermal annealing of precursor at temperatures less than 1000 °C in air leads to formation of Ce_0.5Zr_0.5O₂ powders with cubic fluorite-type structure (Fm-3m). Further increase of annealing temperatures above 1000 °C causes decomposition of formed crystal structure into two phases: cubic and tetragonal. Annealing in reduction hydrogen atmosphere causes formation of Ce₄ + 2xCe₃ + 2-2xZr₂O₇ + x compounds with intermediate valency of cerium, where value of x depends on the reducing conditions and treatment parameters of precursor. Annealing in vacuum at 1400 °C strongly reduces the content of Ce₄+ in a powder samples and leads to formation of pyrochlore structure (space group Fd-3_m) with practically Ce³⁺ valence state.