High-performing thermoelectric materials such as Zn4Sb3and clathrates have atomic disorder as the root to their favorable properties. This makes it extremely difficult to understand and model their properties at a quantitative level, and thus effective structure–property relations are challenging to obtain. Cu2−xSe is an intensely studied, cheap and non-toxic high performance thermoelectric, which exhibits highly peculiar transport properties, especially near the β-to-α phase transition around 400 K, which must be related to the detailed nature of the crystal structure. Attempts to solve the crystal structure of the low-temperature phase, β-Cu2−xSe, have been unsuccessful since 1936. So far, all studies have assumed that β-Cu2−xSe has a three-dimensional periodic structure, but here we show that the structure is ordered only in two dimensions while it is disordered in the third dimension. Using the three-dimensional difference pair distribution function (3D-ΔPDF) analysis method for diffuse single-crystal X-ray scattering, the structure of the ordered layer is solved and it is shown that there are two modes of stacking disorder present which give rise to an average structure with higher symmetry. The present approach allows for a direct solution of structures with disorder in some dimensions and order in others, and can be thought of as a generalization of the crystallographic Patterson method. The local and extended structure of a solid determines its properties and Cu2−xSe represents an example of a high-performing thermoelectric material where the local atomic structure differs significantly from the average periodic structure observed from Bragg crystallography.

中文翻译：

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使用三维差分对分布函数求解 β-Cu2−xSe 的无序结构

锌等高性能热电材料4锑3包合物的原子无序性是其良好特性的根源。这使得在定量水平上理解和模拟它们的性质变得极其困难，因此很难获得有效的结构-性质关系。铜2−XSe 是一种经过深入研究、廉价且无毒的高性能热电材料，它表现出非常奇特的输运特性，特别是在 400 K 左右的 β 到 α 相变附近，这一定与晶体结构的详细性质有关。尝试解析低温相β-Cu的晶体结构2−XSe，自 1936 年以来一直没有成功。到目前为止，所有研究都假设 β-Cu2−XSe具有三维周期结构，但这里我们表明该结构仅在二维中有序，而在三维中是无序的。利用漫射单晶X射线散射的三维差分对分布函数(3D-ΔPDF)分析方法，求解了有序层的结构，并表明存在两种模式的堆积无序，从而产生堆积无序。到具有更高对称性的平均结构。本方法允许直接解决在某些维度上无序而在其他维度上有序的结构，并且可以被认为是晶体学帕特森方法的推广。固体的局部和扩展结构决定了它的性质和 Cu2−XSe 代表了高性能热电材料的一个例子，其中局部原子结构与布拉格晶体学观察到的平均周期结构显着不同。