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Niobate and Tantalate Pyrochlores: Soft Synthesis by the Fluoride Route
Author(s) -
Britvin Sergey N.,
Siidra Oleg I.,
Lotnyk Andriy,
Krivovichev Sergey V.,
Depmeier Wulf
Publication year - 2010
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.200900999
Subject(s) - tantalate , chemistry , aqueous solution , hydrothermal synthesis , sodalite , fluoride , pyrochlore , ion , crystallography , nanocrystalline material , inorganic chemistry , hydrothermal circulation , nuclear chemistry , zeolite , ferroelectricity , chemical engineering , organic chemistry , materials science , dielectric , optoelectronics , phase (matter) , engineering , catalysis
A series of pyrochlores A(Nb,Ta) 2 (O,OH,F) 6 ( n H 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) · n H 2 O and K 1– x Nb 2 (O,OH) 5 F · n H 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 · n H 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.