Synthesis, crystal structure and thermoelectric properties of a new metal telluride Ba₃Ag₃InTe₆

A new metal telluride Ba₃Ag₃InTe₆ was synthesized by a solid-state reaction at 650 °C. Crystal data: Orthorhombic, Cmc2₁, a = 4.5669(3) Å, b = 27.9366(16) Å, c = 13.3819(8) Å, V = 1707.3(2) ų, and Z = 4. This compound adopts a new two-dimensional structure constructed by AgTe₄ and InTe₄ tetrahedra and Ba²⁺ cations. The edge-sharing AgTe₄ tetrahedra form a puckered layer of [Ag₃Te₄]^5- and the corner-sharing InTe₄ tetrahedra form a zig-zag chain of [InTe₂]^- that dangles from both edges of the layer. The band gap determined by UV-vis-NIR absorption spectra is estimated to be around 0.48 eV. This compound is a p-type semiconductor with high Seebeck coefficients of 325-334 μV K^-1 in an entire temperature range of 320-400 K. The electrical conductivity of 9.4 S cm^-1 and the thermal conductivity of 0.35 W mK^-1 give a ZT value of 0.11 at 400 K. The electronic band structure reveals a direct band gap at the Γ point of the face centered primitive Brillouin zone. The density of states (DOS) analysis shows that the p-type hole transport is mostly achieved through the layer consisting of AgTe₄ tetrahedra.