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

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.

通过采用标准的固态技术，以Na2CO3、Nb2O5和TeO2作为试剂，成功合成了两种新型的混合金属碲化物Na1.4Nb3Te4.9O18和NaNb3Te4O16。通过单晶X射线衍射技术确定了Na1.4Nb3Te4.9O18和NaNb3Te4O16的结构。这两种材料均展现出由NbO6八面体、TeO4和TeO3多面体构成的三维结构。Nb5+和Te4+阳离子处于非对称配位环境中，这是由于二阶Jahn−Teller（SOJT）效应所致。Nb5+阳离子经历向角方向（局部C4方向）的内八面体畸变，而Te4+阳离子则因非键合电子对而处于畸变环境。此外，对所报道的材料进行了红外光谱、拉曼光谱、紫外−可见漫反射光谱、热重分析和介电性能测量。晶体数据：Na1.4Nb3Te4.9O18，单斜晶系，空间群C2/m（编号12），晶胞参数a = 32.377(5) Å，b = 7.4541(11) Å，c = 6.5649(9) Å，β = 95.636(5)°，体积V = 1576.7(4) Å3，原子数Z = 4；NaNb3Te4O16，单斜晶系，空间群P21/m（编号11），晶胞参数a = 6.6126(13) Å，b = 7.4738(15) Å，c = 14.034(3) Å，β = 102.98(3)°，体积V = 675.9(3) Å3，原子数Z = 2。