Metal Flux Growth, Structural Relations, and Physical Properties of EuCu2Ge2 and Eu3T2In9 (T = Cu and Ag)

Single crystals (SCs) of the compounds Eu3Ag2In9 and EuCu2Ge2 were synthesized through the reactions run in liquid indium. Eu3Ag2In9 crystallizes in the La3Al11 structure type [orthorhombic space group (SG) Immm] with the lattice parameters: a = 4.8370(1) Å, b = 10.6078(3) Å, and c = 13.9195(4) Å. EuCu2Ge2 crystallizes in the tetragonal ThCr2Si2 structure type (SG I4/mmm) with the lattice parameters: a = b = 4.2218(1) Å, and c = 10.3394(5) Å. The crystal structure of Eu3Ag2In9 is comprised of edge-shared hexagonal rings consisting of indium. The one-dimensional chains of In6 rings are shared through the edges, which are further interconnected with other six-membered rings forming a three-dimensional (3D) stable crystal structure along the bc plane. The crystal structure of EuCu2Ge2 can be explained as the complex [CuGe](2+δ)– polyanionic network embedded with Eu ions. These polyanionic networks present in the crystal structure of EuCu2Ge2 are shared through the edges of the 011 plane containing Cu and Ge atoms, resulting in a 3D network. The structural relationship between Eu3T2In9 and EuCu2Ge2 has been discussed in detail, and we conclude that Eu3T2In9 is the metal deficient variant of EuCu2Ge2. The magnetic susceptibilities of Eu3T2In9 (T = Cu and Ag) and EuCu2Ge2 were measured between 2 and 300 K. In all cases, magnetic susceptibility data followed Curie–Weiss law above 150 K. Magnetic moment values obtained from the measurements indicate the probable mixed/intermediate valent behavior of the europium atoms, which was further confirmed by X-ray absorption studies and bond distances around the Eu atoms. Electrical resistivity measurements suggest that Eu3T2In9 and EuCu2Ge2 are metallic in nature.本研究通过液态铟（liquid indium）介导的合成反应，制备得到Eu₃Ag₂In₉与EuCu₂Ge₂两种化合物的单晶（single crystals, SCs）。Eu₃Ag₂In₉属于La₃Al₁₁结构类型，空间群（space group, SG）为正交晶系的Immm，晶格参数为：a=4.8370(1) 埃（Å），b=10.6078(3) 埃，c=13.9195(4) 埃。EuCu₂Ge₂属于四方晶系的ThCr₂Si₂结构类型，空间群为I4/mmm，晶格参数为a=b=4.2218(1) 埃，c=10.3394(5) 埃。Eu₃Ag₂In₉的晶体结构由铟原子构成的共边六元环所组成，由In₆环构成的一维链通过共边相互连接，进一步与其他六元环互联，最终沿bc晶面形成三维（three-dimensional, 3D）稳定晶体结构。EuCu₂Ge₂的晶体结构可视为嵌入铕离子的复杂[CuGe](2+δ)⁻多阴离子网络，此类多阴离子网络通过包含铜与锗原子的011晶面的共边进行连接，最终形成三维网络结构。本研究详细讨论了Eu₃T₂In₉（T=Cu、Ag）与EuCu₂Ge₂之间的结构关联，并得出结论：Eu₃T₂In₉是EuCu₂Ge₂的金属缺陷变体。本研究在2~300 K温度区间内，测试了Eu₃T₂In₉（T=Cu、Ag）与EuCu₂Ge₂的磁化率，所有样品的磁化率数据在150 K以上均符合居里-外斯（Curie–Weiss）定律。测试得到的磁矩数值表明，铕原子可能存在混合价态/中间价态行为，该结论通过X射线吸收光谱研究以及铕原子周围的键长数据得到了进一步验证。电阻率测试结果表明，Eu₃T₂In₉与EuCu₂Ge₂均表现出金属性导电特性。