Oligomerization Versus Polymerization of Te<i>_x</i><i>ⁿ</i>^- in the Polytelluride Compound BaBiTe₃. Structural Characterization, Electronic Structure, and Thermoelectric Properties

Abstract

The compound BaBiTe3 was prepared by the reaction of Ba/Bi/Te at over 700 °C in either K2Te4 or BaTe3 flux and was recrystallized in a Ba/BaTe3 flux. The black rod-shaped polycrystalline material crystallizes in the orthorhombic space group P212121 (no. 19) with a = 4.6077(2) Å, b = 17.0437(8) Å, c = 18.2997(8) Å, V = 1437.1(2) Å3, Z = 8, and dcalc = 6.74 g/cm3. Number with Fo2 > 3σ(Fo)2 3373, number of variables 92, and sin (θ/λ) < 0.7. The final R/Rw = 4.55/5.61%. The structure is BaBiSe3 type and may be described as layers made up from interdigitating columnar [Bi4Te10(Te2)]∞ “herring-bone” shaped segments. Ba2+ 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 Ba2+4Bi3+4Te2-8Te1-4. 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.