Specific structural features of LnZrOx (Ln: La, Sm) mixed oxides prepared by
different methods |
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Authors: | Tatyana Kuznetsov Tamara Kriger Yurii Chesalov Andrey Boronin Arcadii Ishchenko Pavlos K Pandis Vladimir Krivensov Galina Litvak Tatyana Larin Vladislav Sadykov and Vassilis N Stathopoulos |
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Institution: | 1. Boreskov Institute of Catalysis, Pr. Lavrentieva, 5, 630090 Novosibirsk, Russian Federation;2. Novosibirsk State University, 630090 Novosibirsk, Russian Federation;3. Laboratory of Chemistry and Materials Technology, Department of Electrical Engineering, School of Technological Applications, Technological Education Institute of Sterea Ellada, 34400 Psachna campus, Evia, Greece |
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Abstract: | LnZrOx (Ln: La, Sm) mixed oxides of Ln: Zr?=?1 were prepared by different methods (complex polymerized method, sorption of cations on starch from aqueous salt solution and conventional co-precipitation with additional redispersion of precipitate by ultra sound) and calcined at 700–1300?°C. Their specific structural features and changes were studied and discussed. Various characterization methods were used such as X-ray diffraction, Electron microscopy, Fourier-transform infrared and Raman spectroscopy, UV–Vis spectroscopy, X-Ray absorption fine structure and X-ray photoelectron spectroscopy.The formation of pyrochlore structure occurred at 1100–1300?°C from fluorite-like pseudocubic phase ZrO2 regardless the method of preparation. This phase had a block-like structure consisting of ZrO2 nanocrystals stabilized by Ln cations and residual anions such as hydroxyls and carbonates. The desorption of such anions with heating already started at 900?°C and lead to local changes of Zr cations coordination to octahedral and to the formation of pyrochlore nanodomains inclusions within fluorite-like phase. The increased cation mobility and further elimination of anions caused by further heating was accompanied by the formation of bulk pyrochlore phase at 1100–1300?°C. Even after calcination at 1300?°C the local microheterogeneity as well as defects were identified at domains boundaries or sintered microstructure. These specific features of the formed pyrochlores depend on the method of preparation. |
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Keywords: | Fluorites Pyrochlores Synthesis Powders Structure |
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