Ba₄in₈Sb₁₆: Thermoelectric properties of a new layered zintl phase with infinite Zigzag Sb chains and pentagonal tubes

A new Zintl phase Ba₄In₈Sb₁₆ was obtained from a direct element combination reaction of the elements in a sealed graphite tube at 700°C, and its structure was determined by single-crystal X-ray diffraction methods. It crystallizes in the orthorhombic space group Pnma (No. 62) with a = 10.166(3) Å, b = 4.5239(14) Å, c = 19.495(6) Å, and Z = 1. Ba₄In₈Sb₁₆ has a two-dimensional structure with thick corrugated (In₈Sb₁₆)^8- layers separated by Ba²⁺ ions. In the layer, InSb₄ tetrahedra are connected by sharing three corners and by bridging the fourth corner in such a manner that infinite pentagonal tubes are formed. The compound is a narrow band gap (∼ 0.10 eV) semiconductor and satisfies the classical Zintl rule. Band structure calculations confirm that the material is a semiconductor and indicate that it has optimized In-Sb bonding interactions. Polycrystalline ingots of Ba₄In₈Sb₁₆ show room-temperature electrical conductivity of 135 S/cm and a Seebeck coefficient of 70 μV/K. The thermal conductivity of Ba₄In₈Sb₁₆ is about 1.7 W/m·K in the temperature range 150-300 K.