Non-stoichlometric mixed lead and tin niobates


Novel non-stoichiometric mixed lead and tin niobates with the pyrochlore structure have been synthesized via a solid-state route. The materials have been characterized by bulk chemical analysis, single-crystal and powder X-ray diffraction, Pb-207, Sn-119 and Nb-93 (single and triple quantum) solid-state NMR spectroscopy. The structures of the new non-stoichiometric mixed lead-tin niobate pyrochlore compounds have been Rietveld refined in the cubic system, space group Fd-3m. The steroactivity of the Sn(II) free electron pair leads to the general formula (Sn1.6-xPbx)(Nb2-ySny)O6.6-0.5,where x (0-1.6) is the Pb(II) and y (0-0.34) is the Sn(IV) contents. Pb-207, Sn-119 and (in particular) Nb-93 NMR support the isornorphous substitution of tin for lead in the compounds studied. Nb-93 triple-quantum magic-angle spinning NMR spectroscopy show that the materials contain, at least, two distinct niobium sites, in a 2:1 population ratio, which may be associated with different sample domains. (C) 2003 Elsevier Inc. All rights reserved.



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Cruz, LP; Savariault, JM; Morais, CM; Fernandez, C; de Jesus, JDP; Rocha, J

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