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 degrees 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) Angstrom, b = 4.5239(14) Angstrom, c = 19.495(6) Angstrom, and Z = 1. Ba4In8Sb18 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 (similar to 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 mu V/K. The thermal conductivity of Ba4In8Sb16 is about 1.7 W/m.K in the temperature range 150-300 K.