Synthesis and characterization of tin niobates

The synthesis and the structural characterization of tin niobates Sn1+xNb2O 6+x, x = 0.0, 0.5, and 1.0, are reported. The materials have been character ized by bulk chemical analysis, single-crystal and powder X-ray diffraction , and Sn-119 Mossbauer and Nb-93 and Sn-119 solid-state NMR spectroscopies. SnNb2O6 is a synthetic analog of the rare mineral foordite. Red Sn2Nb2O7 c rystallizes in a pyrochlore structure with a = 10.5386 Angstrom. Sn-119 Mos sbauer reveals the presence of both Sn(II) and Sn(IV) in pyrochlore samples . Sn-119 MAS NMR spectroscopy supports the presence in synthetic foordite o f Sn(II) in eight-fold coordination. The six-coordinated Sn(IV) and eight-c oordinated Sn(II) Sn-119 MAS NMR resonances are not resolved in the Sn2Nb2O 7 pyrochlore spectrum. Nb-93 NMR indicates a fairly distorted local environ ment for niobium in synthetic foordite, much more so than in the Sn2Nb2O7 p yrochlore. (C) 2001 Academic Press.