Stracture and thermoelectric properties of the new quaternary tin selenide K(1-x)Sn(5-x)Bi(11+x)Se₂₂

Silver colored ribbon-like crystals of K(1-x)Sn(5-x)Bi(11+x)Se₂₂ (x≃0.33) were prepared by direct combination of K₂Se, Bi₂Se₃, Sn and Se at 800 °C. A structure determination was carried out for K_{0. 66}Sn_4.82Bi_11.18Se₂₂. Bi₂Te₃-type and NaCl-type building units are connected to form a new kind of three-dimensional anionic framework with K+ filled tunnels. The building units are assembled from distorted, edge- sharing (Bi,Sn)Se₆ octahedra. Bi and Sn atoms are disordered over all metal sites of the chalcogenide network while the K site is only one third occupied. The charge transport measurements of K_0.66Sn_4.82Bi_11.18Se₂₂ at room temperature reveal an electrical conductivity of 450 S cm^-1 and a thermopower of -43 μV K^-1. The thermal conductivity is 1.5 W m^-1 K^-1. An optical band gap of approximately 0.12 eV was determined at room temperature. K_0.66Sn_4.82Bi_11.18Se₂₂ melts congruently at 680 °C.