Oligomerization Versus Polymerization of Texn⁻ in the Polytelluride Compound BaBiTe₃. Structural Characterization, Electronic Structure, and Thermoelectric Properties

The compound BaBiTe 3 was prepared by the reaction of Ba/Bi/Te at over 700 °C in either K 2 Te 4 or BaTe 3 flux and was recrystallized in a Ba/BaTe 3 flux. The black rod-shaped polycrystalline material crystallizes in the orthorhombic space group P 2 1 2 1 2 1 (no. 19) with a = 4.6077(2) Å, b = 17.0437(8) Å, c = 18.2997(8) Å, V = 1437.1(2) Å 3, Z = 8, and d calc = 6.74 g/cm 3 . Number with F o 2 > 3σ(F o ) 2 3373, number of variables 92, and sin (θ/λ) < 0.7. The final R / R w = 4.55/5.61%. The structure is BaBiSe 3 type and may be described as layers made up from interdigitating columnar [Bi 4 Te 10 (Te 2 )] ∞ “herring-bone” shaped segments. Ba 2+ ions are in distorted tri-capped trigonal prismatic sites between the layers. From band structure calculations, a formal charge distribution taking into account the occurrence of short-bonding Te···Te contacts in the structure can be written as Ba 2+ 4 Bi 3+ 4 Te 2 - 8 Te 1- 4 . The electrical conductivity, thermopower, thermal lattice conductivity, and infrared absorption properties of this material suggest that it is a narrow gap semiconductor. These results are discussed in the context of the band scheme.