The combination of divalent Eu with high magnetic moment and strong spin-orbit coupling (SOC) on Pd or Pt atoms in a single substance, makes Eu-Pd/Pt-X ternary phases attractive for materials with exotic physical properties. For that reason, compositions according to Eu2M2X (M = Pd, Pt; X = Al, Ga, Ge, Cd) were explored. X-ray diffraction analyses revealed that the three Pd analogues Eu2Pd2Al, Eu2Pd2Ga, and Eu2Pd2Ge crystallize isostructural to Ca2Pd2Ge, a ternary ordered variant of the Zr2Al3-type (orthorhombic Fdd2). In contrast, Eu2Pt2Al adopts the Ca2Ir2Si type rival structure (monoclinic C2/c). The two structure types are closely related as they both feature linear chains of the noble metals, with the X atoms bridging the metal chains from adjacent layers. However, a striking difference is noticeable within the metal chains: The Pd linear chains consist of equidistant PdPd atoms (2.96 Å), whereas in the Pt chains are pairwise distorted with alternating shorter (Pt–Pt = 2.80 Å) and longer (2.98 Å) contacts. The pairwise distortion is, at first glance, attributed to stronger relativistic influence on Pt atom. In addition, Eu2Pt2Cd, adopts the W2CoB2 type, suggesting that the valence electron count (vec) has strong influence in the structure selection. Finally, both Ca2Pd2Ge- and Ca2Ir2Si-type structures are also discussed as defect Laves phases in connection with the newly discovered phase Ca2Pt3Al1–xAgx (x = 0.13(1)) which adopts the TbFe2 type structure (space group R-3m). DFT first principles electronic band structure calculations, conducted on the Ag-free ordered model “Ca2Pt3Al”, suggested that Ag-inclusion is mainly due to geometric factors, while the chemical bonding picture is consistent with a polar intermetallic system.

中文翻译：

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含贵金属 Eu2M2X（M = Pd、Pt；X = Al、Ga、Ge、Cd）的富铕三元相及其与 Laves 相 Ca2Pt3Al1-xAgx 的结构关系

二价 Eu 与单一物质中的 Pd 或 Pt 原子上的高磁矩和强自旋轨道耦合 (SOC) 相结合，使得 Eu-Pd/Pt-X 三元相对于具有奇异物理性质的材料具有吸引力。因此，我们探索了符合 Eu2M2X（M = Pd、Pt；X = Al、Ga、Ge、Cd）的成分。 X射线衍射分析表明，三种Pd类似物Eu2Pd2Al、Eu2Pd2Ga和Eu2Pd2Ge同构结晶为Ca2Pd2Ge，Ca2Pd2Ge是Zr2Al3型（正交Fdd2）的三元有序变体。相比之下，Eu2Pt2Al采用Ca2Ir2Si型竞争结构（单斜晶系C2/c）。这两种结构类型密切相关，因为它们都具有贵金属的线性链，X原子桥接相邻层的金属链。然而，金属链中存在显着差异：Pd 线性链由等距的 PdPd 原子 (2.96 Å) 组成，而 Pt 链则成对扭曲，较短 (Pt-Pt = 2.80 Å) 和较长 (2.98 Å) 交替出现。 ）联系人。乍一看，成对畸变归因于 Pt 原子更强的相对论影响。此外，Eu2Pt2Cd采用W2CoB2型，表明价电子数（vec）对结构选择有很大影响。最后，Ca2Pd2Ge 和 Ca2Ir2Si 型结构也被讨论为缺陷 Laves 相，与新发现的采用 TbFe2 型结构（空间群 R-3m）的 Ca2Pt3Al1–xAgx (x = 0.13(1)) 相相关。在无银有序模型“Ca2Pt3Al”上进行的DFT第一原理电子能带结构计算表明，Ag的夹杂主要是由于几何因素，而化学键合图与极性金属间化合物体系一致。