Effect of the Synthesis Conditions on the Crystal, Local, and Electronic Structures of Ce2x4+Ce2-2x3+M2O7 + x (M = Zr, Hf).

Autor: Popov, V. V., Menushenkov, A. P., Khubbutdinov, R. M., Yastrebtsev, A. A., Sharapov, A. S., Zubavichus, Ya. V., Svetogorov, R. D., Trigub, A. L., Tsarenko, N. A., Arzhatkina, L. A., Kurilkin, V. V.
Zdroj: Russian Journal of Inorganic Chemistry; Apr2018, Vol. 63 Issue 4, p503-511, 9p
Abstrakt: The effect of synthesis conditions (type of cations, annealing temperature, reductive or oxidative atmosphere) on the chemical composition and structure of compounds formed in the MO2-CeO2/Ce2O3 systems (M = Zr, Hf) was studied by X-ray diffraction, X-ray absorption spectroscopy, Raman spectroscopy, and thermogravimetric analysis. The isothermal annealing of the precursors at temperatures below 1000°C in air gives Ce0.5M0.5O2 powders with fluorite type cubic structure (space group Fm3̅m). High-temperature annealing above 1000°C gives rise to additional tetragonal (space group P42/nmc) (for zirconates) or monoclinic (space group P21/a) (for hafnates) phases. The annealing in a hydrogen atmosphere affords the compounds Ce2x4+Ce2-2x3+M2O7 + x with an intermediate oxidation state of cerium and the x value depending on both the reduction conditions and the pre-annealing parameters. Vacuum annealing at 1400°C considerably decreases the content of Ce(IV) in the samples and affords a pyrochlore structure (space group Fd3̅m) with predominating Ce(III) cations. [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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