Severe Ge segregation to grain boundaries was observed in a Si–14.2 at% Ge thermoelectric alloy rapidly solidified using a drop-tube facility, manifesting itself as a series of regions with uniform stoichiometric compositions. The step change in composition at the interface between adjacent regions was ascribed to the formation of different SiGe pseudocompounds and contradicted the accepted thermodynamic description of the SiGe system as a continuous random solid solution. Rapid solidification increased, rather than decreased, the inhomogeneity degree of the solid product, and the Ge content of the most Ge-rich regions was positively correlated with the cooling rate, which suggested the absence of solute trapping. The transmission electron microscopy/selected area electron diffraction analysis of the most Ge-rich regions revealed superlattice spots indicative of chemical ordering. However, simple chemical ordering within a single diamond cubic unit cell could not explain the fact that most stoichiometries had compositions that were multiples of 5 at% Ge, which indicated the presence of superstructural ordering.

中文翻译：

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快速凝固硅锗合金的微观结构表征和化合物形成

在使用滴管设备快速凝固的 Si-14.2 at% Ge 热电合金中观察到严重的 Ge 偏析到晶界，表现为一系列具有均匀化学计量成分的区域。相邻区域之间界面处成分的阶跃变化归因于不同 SiGe 赝化合物的形成，并且与公认的 SiGe 系统作为连续随机固溶体的热力学描述相矛盾。快速凝固增加而不是减少了固体产物的不均匀程度，并且最富Ge区域的Ge含量与冷却速率呈正相关，这表明不存在溶质捕获。最富含Ge区域的透射电子显微镜/选定区域电子衍射分析揭示了表明化学有序性的超晶格点。然而，单个金刚石立方晶胞内的简单化学排序无法解释大多数化学计量的组成是 5 at% Ge 的倍数的事实，这表明上层结构排序的存在。