Eu5In2Sb6, Eu5In2-xZnxSb6: rare earth zintl phases with narrow band gaps

The new Zintl phase Eu5In2Sb6 was obtained from a direct element combination reaction in a sealed graphite tube at 870degreesC and its structure was determined. It crystallizes in the orthorhombic space group Pbam(No. 55), with a unit cell of a=12.510(3)Angstrom, b=14.584(3) Angstrom, c=4.6243(9) Angstrom, and Z=2. Eu5In2Sb6 shows the Ca5Ga2As6-type structure and has a one-dimensional structure with infinite anionic double chains [In2Sb6](10-) separated by Eu2+ ions. Each single chain is made of corner sharing InSb4 tetrahedra. Two such tetrahedral chains are bridged by a Sb-2 group to form double chains. The compound satisfies the classical Zintl concept and is a narrow band gap semiconductor. The substitution of Zn for In atoms in Eu5In2Sb6 resulted in an increase in hole concentration and the material is more metallic. Polycrystalline ingots of Eu5In2Sb6 and Eu5In2-xZnxSb6 showed electrical conductivity of similar to36 S cm(-1), similar to146 S cm(-1) and Seebeck coefficient of similar to76 muV K-1 and similar to51 muV K-1 at room temperature, respectively.