Synthesis, structure and charge transport properties of Yb ₅Al ₂Sb ₆: 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, Yb ₅AI ₂Sb ₆. The compound crystallizes in the Ba ₅AI ₂Bi ₆ structure type and requires the addition of Ge or Si in the synthesis, which appears to act as a catalyst. Yb ₅AI ₂Sb ₆ has an anisotropic structure with infinite anionic double chains cross-linked by Yb ²⁺ ions. Polycrystalline ingots of Yb ₅Al ₂Sb ₆ 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 Yb ₅AI ₂Sb ₆, doping effects, and chemical modifications are discussed. Sr only partially replaces Yb in the structure leading to Sr _0.85Yb _4.15AI ₂Sb ₆. 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.