The presence of ns 2 stereo-chemical active lone electron pairs (LEPs) causes asymmetric atomic environments around a given p-block cation, leading to change the crystal chemistry of a respective system. Here we report a series of mullite-type compounds to understand at what extend Sr2+ replaces the stereochemical active Pb2+ cation in (Pb1−x Sr x )MnBO4. Each member of the solid solution has been synthesized by conventional solid-state method. The polycrystalline samples are characterized using X-ray powder diffraction followed by Rietveld refinement. Substitution of Pb2+ with Sr2+ leads to contraction of the a lattice parameter with slight elongation in the b and c direction. For a difference of 1 pm of the ionic radius between Sr2+ and Pb2+, the cell volume contracts about 4 % between the end members as the spatial requirement of the LEP activity in the MBO4 2− channels significantly decreases. Within the solid solution, two distinct Pb/Sr–O2 bond distances significantly differ, which gradually decreases with increasing strontium content leading to a more symmetric coordination around strontium. The calculated BVS of Pb2+/Sr2+ exhibits a linear correlation with the Wang–Liebau eccentricity parameter, indicating to an increased bonding ability cation. The vibrational properties are characterized by both Raman and FTIR spectroscopy, complementing the XPRD results. Electronic band gaps of selected (Pb1−x Sr x )MnBO4 samples were obtained from diffuse reflectance spectroscopy data. Additionally, the Sr containing samples show higher thermal stability than the Pb containing counterparts.

中文翻译：

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(Pb1−x Sr x )MnBO4 的合成和表征：结构和光谱研究

的存在纳秒 2立体化学活性孤电子对 (LEP) 会导致给定周围的原子环境不对称p-阻断阳离子，导致改变各自系统的晶体化学。在这里，我们报告了一系列莫来石型化合物，以了解 Sr 的程度2+取代立体化学活性 Pb2+阳离子 (Pb1−X 锶 X ) 硼酸锰4。固溶体的每个成员都是通过常规固相方法合成的。使用 X 射线粉末衍射和 Rietveld 精修对多晶样品进行表征。替代铅2+与锶2+导致收缩A轻微伸长的晶格参数乙和C方向。对于 Sr 之间的离子半径相差 1 pm2+和铅2+，由于 MBO 中 LEP 活动的空间要求，端部成员之间的细胞体积收缩约 4 %4 2−渠道明显减少。在固溶体中，两种不同的 Pb/Sr-O2键距显着不同，随着锶含量的增加而逐渐减小，导致锶周围的配位更加对称。计算出的 Pb 的 BVS2+/锶2+与 Wang-Liebau 偏心率参数呈线性相关，表明阳离子键合能力增强。振动特性通过拉曼光谱和 FTIR 光谱进行表征，补充了 XPRD 结果。选定的电子带隙（Pb1−X 锶 X ) 硼酸锰4样品是从漫反射光谱数据获得的。此外，含 Sr 的样品比含 Pb 的样品表现出更高的热稳定性。