Niobate and Tantalate Pyrochlores: Soft Synthesis by the Fluoride Route

Britvin, S. N., Siidra, O. I., Lotnyk, A., Krivovichev, S. V. and Depmeier, W. (2010) Niobate and Tantalate Pyrochlores: Soft Synthesis by the Fluoride Route European Journal of Inorganic Chemistry (7). pp. 1082-1088. DOI 10.1002/ejic.200900999.

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A series of pyrochlores A(Nb,Ta)(2)(O,OH,F)(6)(nH(2)O), (A = NH(4), K, Rb, Cs) have been synthesized by hydrolysis of aqueous solutions of oxofluoroniobic (H(2)NbOF(5)) and fluorotantalic (H(2)TaF(7)) acids. This new method allows preparation of nanocrystalline niobate pyrochlores (crystal size 10-20 nm) by simple precipitation with subsequent boiling; tantalate analogues can be obtained by soft hydrothermal treatment. The synthesized compounds include new pyrochlores NH(4)Nb(2)O(5)(OH,F), NH(4)Ta(2)O(5)(OH,F)center dot nH(2)O and K(1-x)Nb(2)(O,OH)(5)F center dot nH(2)O as well as the already known CsNb(2)O(5)F, Rb(1-x)Nb(2)(O,OH)(5)F, CsTa(2)O(5)F and their hydroxyl analogues. Ion-exchange experiments revealed that K(0.7)Nb(2)(O,OH)(5)F center dot nH(2)O exhibits strong selective uptake of Pb(2+) from aqueous solutions, a feature not previously reported for pyrochlores. The facilitating role of fluoride ions in the synthesis of pyrochlores is discussed in comparison with zeolite synthesis, and the technological applicability of the new method is also presented in the paper.

Document Type: Article
Keywords: Niobium Tantalum Sol-gel processes Nanostructures Ion exchange hydrofluoric-acid solutions ion-exchange properties mixed-metal oxides hydrothermal synthesis defect pyrochlore crystal-structure solid-state niobium complexes nh4nbwo6
Research affiliation: Kiel University
DOI etc.: 10.1002/ejic.200900999
ISSN: 1434-1948
Date Deposited: 22 Dec 2011 05:52
Last Modified: 08 Oct 2012 09:59

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