Yb5In2Sb6: A new rare earth zintl phase with a narrow band cap

The new Zintl phase Yb5In2Sb6 was obtained from a direct element combinatio n reaction in a sealed graphite tube at 700 degreesC 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) Angstrom , b = 23.001(6) Angstrom, c = 4.5139(4) Angstrom, 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 InSb 4 tetrahedra. Two such chains are bridged by Sb-2 groups to form double cha ins 1/infinity [In2Sb610-]. The compound satisfies the classical Zintl conc ept and is a narrow gap semiconductor. Band structure calculations suggest an direct band gap. Polycrystalline ingots of Yb5In2Sb6 showed electrical c onductivity of 100 S/cm and a Seebeck coefficient of similar to +30 mu 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.