Synthesis, Structure and Charge Transport Properties of Yb5Al2Sb6: A Zintl Phase with Incomplete Electron Transfer

We report the synthesis, structure, spectroscopic properties, charge and thermal transport, and electronic structure of a new member of the Zintl family, Yb5Al2Sb6. The compound crystallizes in the Ba5Al2Bi6 structure type and requires the addition of Ge or Si in the synthesis, which appears to act as a catalyst. Yb5Al2Sb6 has an anisotropic structure with infinite anionic double chains cross-linked by Yb2+ ions. Polycrystalline ingots of Yb5Al2Sb6 prepared in the presence of 0.5 mol equiv of Ge showed room-temperature conductivity, thermopower, and thermal conductivity of ∼1100 S/cm, ∼20 μV/K, and ∼3.8 W/m·K, respectively. Investigations of other solid solutions of Yb5Al2Sb6, doping effects, and chemical modifications are discussed. Sr only partially replaces Yb in the structure leading to Sr0.85Yb4.15Al2Sb6. Electronic structure calculations performed using a highly precise full-potential linearized augmented plane wave method within the density functional theory scheme show the presence of a negative band gap and suggest incomplete electron transfer and a metallic character to the compound.

本研究报告了一种新的Zintl系列成员Yb5Al2Sb6的合成、结构、光谱性质、电荷及热传输特性，以及电子结构。该化合物以Ba5Al2Bi6结构类型结晶，并在合成过程中需加入Ge或Si，似乎作为催化剂发挥作用。Yb5Al2Sb6呈现出各向异性结构，由无限延伸的阴离子双链通过Yb2+离子交联。在0.5摩尔当量Ge的存在下制备的Yb5Al2Sb6多晶锭，在室温下表现出约1100 S/cm的电导率、约20 μV/K的热电势和约3.8 W/m·K的热导率。此外，对Yb5Al2Sb6的其他固溶体、掺杂效应及化学改性进行了探讨。Sr仅部分取代Yb，形成了Sr0.85Yb4.15Al2Sb6。在密度泛函理论框架内，采用高精度全势线性化增广平面波方法进行的电子结构计算表明，该化合物存在负能带隙，并暗示了电子转移的不完全性和金属特性。