Synthesis and Characterization of Tin Niobates

摘要

The synthesis and the structural characterization of tin nio- bates Sn_(l+x)Nb_2O_6+x, X = 0.0, 0.5, and 1.0, are reported. The materials have been characterized by bulk chemical analysis, single-crystal and powder X-ray diffraction, and 119Sn Mossbauer and 93Nb and 119Sn solid-state NMR spectroscopies. SnNb_2O_6 isa synthetic analog of the rare mineral foordite. Red Sn_2Nb_2O_7 crystallizes in a pyrochlore structure with a = 10.5386 A. 119Sn Mossbauer reveals the presence of both Sn(I1) and Sn(IV) in pyrochlore samples. 119Sn MAS NMR spectroscopy supports the presence in synthetic foordite of Sn(Il) in eight-fold coordination. The six-coordinated Sn(IV) and eight-coordinated Sn(Il) 119Sn MAS NMR resonances are not resolved in the Sn2Nb_2O_7 pyro- chlore spectrum. 93Nb NMR indicates a fairly distorted local environment for niobium in synthetic foordite, much more so than in the Sn_2N'b_2O_7 pyrochlore.