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Mixed-Metal Tellurites:  Synthesis, Structure, and Characterization of Na1.4Nb3Te4.9O18 and NaNb3Te4O16

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posted on 30.05.2005, 00:00 by Kang Min Ok, P. Shiv Halasyamani
Two new mixed-metal tellurites, Na1.4Nb3Te4.9O18 and NaNb3Te4O16, have been synthesized by standard solid-state techniques using Na2CO3, Nb2O5, and TeO2 as reagents. The structures of Na1.4Nb3Te4.9O18 and NaNb3Te4O16 were determined by single-crystal X-ray diffraction. Both of the materials exhibit three-dimensional structures composed of NbO6 octahedra, TeO4, and TeO3 polyhedra. The Nb5+ and Te4+ cations are in asymmetric coordination environments attributable to second-order Jahn−Teller (SOJT) effects. The Nb5+ cations undergo an intraoctahedral distortion toward a corner (local C4 direction), whereas the Te4+ cations are in distorted environments owing to their nonbonded electron pair. Infrared and Raman spectroscopy, UV−vis diffuse reflectance spectroscopy, thermogravimetric analysis, and dielectric measurements were also performed on the reported materials. Crystal data:  Na1.4Nb3Te4.9O18, monoclinic, space group C2/m (No. 12), with a = 32.377(5) Å, b = 7.4541(11) Å, c = 6.5649(9) Å, β = 95.636(5)°, V = 1576.7(4) Å3, and Z = 4; NaNb3Te4O16, monoclinic, space group P21/m (No. 11), with a = 6.6126(13) Å, b = 7.4738(15) Å, c = 14.034(3) Å, β = 102.98(3)°, V = 675.9(3) Å3, and Z = 2.