Structure and optical properties have been successfully determined for a series of niobium- and tantalum-containing layered alkaline-earth silicate compounds, Ba3(Nb6−xTax)Si4O26 (x = 0.6, 1.8, 3.0, 4.2, 5.4). The structure of this solid solution was found to be hexagonal P-62m (No. 189), with Z = 1. With x increases from 0.6 to 5.4, the lattice parameter a increases from 8.98804(8) to 9.00565(9) Å and c decreases from 7.83721(10) to 7.75212(12) Å. As a result, the volume decreases from 548.304(11) to 544.479(14) Å3. The (Nb/Ta)O6 distorted octahedra form continuous chains along the c-axis. These (Nb/Ta)O6 chains are in turn linked with the Si2O7 groups to form distorted pentagonal channels in which Ba ions were found. These Ba2+ ions have full occupancy and a 13-fold coordination environment with neighboring oxygen sites. Another salient feature of the structure is the linear Si–O–Si chains. When x in Ba3(Nb6−xTax)Si4O26 increases, the bond valence sum (BVS) values of the Ba sites increase slightly (2.09–2.20), indicating the size of the cage becoming progressively smaller (over-bonding). While SiO cages are also slightly smaller than ideal (BVS range from 4.16 to 4.19), the (Nb/Ta)O6 octahedral cages are slightly larger than ideal (BVS range from 4.87 to 4.90), giving rise to an under-bonding situation. The bandgaps of the solid solution members were measured between 3.39 and 3.59 eV, and the x = 3.0 member was modeled by density functional theory techniques to be 3.07 eV. The bandgaps of these materials indicate that they are potential candidates for ultraviolet photocatalyst.

中文翻译：

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Ba3(Nb6−xTax)Si4O26 的结构和光学性质 (x = 0.6, 1.8, 3.0, 4.2, 5.4)

已成功确定了一系列含铌和钽的层状碱土硅酸盐化合物 Ba 的结构和光学性质3（铌6−X塔X)硅4○26(X= 0.6、1.8、3.0、4.2、5.4）。发现这种固溶体的结构是六方的磷-62米（第 189 号），与Z= 1. 有X从 0.6 增加到 5.4，晶格参数一种从 8.98804(8) 增加到 9.00565(9) Å 和C从 7.83721(10) 减少到 7.75212(12) Å。结果，体积从 548.304(11) 减小到 544.479(14) Å3. (Nb/Ta)O6扭曲的八面体沿C-轴。这些 (Nb/Ta)O6链又与 Si 相连2○7基团形成扭曲的五边形通道，其中发现了 Ba 离子。这些巴2+离子具有完全占用和与相邻氧位点的 13 倍配位环境。该结构的另一个显着特征是线性 Si-O-Si 链。什么时候X在巴3（铌6−X塔X)硅4○26增加，Ba 位点的键合价和（BVS）值略有增加（2.09-2.20），表明笼的尺寸逐渐变小（过度键合）。虽然 SiO 笼也略小于理想值（BVS 范围从 4.16 到 4.19），但 (Nb/Ta)O6八面体笼子比理想值略大（BVS 范围从 4.87 到 4.90），从而导致粘合不足的情况。固溶体成员的带隙测量在 3.39 和 3.59 eV 之间，并且X= 3.0 成员通过密度泛函理论技术建模为 3.07 eV。这些材料的带隙表明它们是紫外光催化剂的潜在候选者。