Quaternary Layered Semiconductor BaCrGeSe: Synthesis, Crystal Structure, and Thermoelectric Properties.

A quaternary narrow-band-gap semiconductor, BaCrGeSe, 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 CrSe octahedra that are stacking along the c axis, with dispersed GeSe tetrahedra and located Ba 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 BaCrGeSe sample shows a desirable low thermal conductivity κ (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.