Yb5In2Sb6: A New Rare Earth Zintl Phase with a Narrow Band Gap

The new Zintl phase Yb5In2Sb6 was obtained from a direct element combination reaction in a sealed graphite tube at 700°C and its structure was determined. It crystallizes in the orthorhombic space group Pbam (No. 55), in the Ba5Al2Bi6 structure type, with a unit cell of a=7.3992(5) ?, b=23.001(6) ?, c=4.5139(4) ?, and Z=2. Yb5In2Sb6 has a onedimensional structure with infinite anionic double chains (In2Sb6)10- separated by Yb2+ ions. Each single chain is made of corner-sharing InSb4 tetrahedra. Two such chains are bridged by Sb2 groups to form double chains [In2Sb10-6]. The compound satisfies the classical Zintl concept and is a narrow gap semiconductor. Band structure calculations suggest an direct band gap. Polycrystalline ingots of Yb5In2Sb6 showed electrical conductivity of 100 S/cm and a Seebeck coefficient of ~+30 muV/K at room temperature. The thermal conductivity of Yb5In2Sb6 is about 1.7 W/mK in the temperature range of 150-300 K.