This work expands on the superstructure in the layered oxide Na₂Zn₂TeO₆ (NZTO). The diffractogram contains weak peaks that are not fitted by the average structure but are found to belong to a 2 × 2 × 3 commensurate modulation of the structure. The modulated structure was found by randomizing the starting points to ensure that the global minima are identified. The resulting superstructure is then used to generate a starting structure for reversed Monte Carlo (RMC) fitting of the total scattering data. We identify two structural features that are preserved through both fittings. One is that two of the Zn/Te columns in the layer direction have a significantly higher degree of disorder, with the exchange of Zn and Te. The second feature is that one of the crystallographic Na sites (2a) was found to be empty. The Na atoms are located midway between crystallographic 2a and 6g sites, which surrounds half of the 2a sites. This type of off-centering is found both in the modulated structure and in the corresponding structure preserved through RMC modeling. The results are discussed in relation to variable-temperature solid-state NMR data measured between 100 and 293 K. We suggest that the phenomenon is a feature of a dynamic situation and an important clue to progress the understanding of ion dynamics in more detail.

中文翻译：

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局部无序 Na2Zn2TeO6 的上层结构


这项工作扩展了层状氧化物 Na₂Zn₂TeO₆ （NZTO） 中的超结构。衍射图包含未被平均结构拟合的弱峰，但被发现属于结构的 2 × 2 × 3 相称调制。通过随机化起点来找到调制结构，以确保识别出全局最小值。然后使用得到的上部结构生成总散射数据的反向蒙特卡洛 （RMC） 拟合的起始结构。我们确定了通过两个配件保留的两个结构特征。一个是层方向上的两个 Zn/Te 柱随着 Zn 和 Te 的交换而具有明显更高的无序程度。第二个特征是发现其中一个晶体学 Na 位点 （2a） 是空的。Na 原子位于晶体学 2a 和 6g 位点之间的中间位置，该位点围绕着 2a 位点的一半。这种类型的偏心既存在于调制结构中，也存在于通过 RMC 建模保留的相应结构中。这些结果与在 100 到 293 K 之间测量的可变温度固体 NMR 数据进行了讨论。我们认为，这种现象是动态情况的一个特征，是更详细地理解离子动力学的重要线索。