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) Å, b=23.001(6) Å, c=4.5139(4) Å, and Z=2. Yb₅In₂Sb₆ has a one-dimensional 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 1/∞ [In₂Sb₆/^10-]. 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 μ V/K at room temperature. The thermal conductivity of Yb₅In₂Sb₆ is about 1.7 W/mK in the temperature range of 150-300 K. (C) 2000 Academic Press.