Quaternary Layered Semiconductor Ba₂Cr₄GeSe₁₀: Synthesis, Crystal Structure, and Thermoelectric Properties

A quaternary narrow-band-gap semiconductor, Ba₂Cr₄GeSe₁₀, has been discovered by solid-state reaction. It features a new structure type and crystallizes in the triclinic space group P1̅ (No. 2). The featured 2D anionic layers are constructed by condensed CrSe₆ octahedra that are stacking along the c axis, with dispersed GeSe₄ tetrahedra and located Ba²⁺ cations forming these layers. The energy-band structure shows a clear separation between the region of electronic conduction and the zone of electronic insulation. Significantly, an undoped Ba₂Cr₄GeSe₁₀ sample shows a desirable low thermal conductivity κ_T (0.51-0.87 W/m·K) and a high Seebeck coefficient S (351-404 μV/K) and reaches a ZT ≈ 0.08 at 773 K.