Structure and thermoelectric properties of the new quaternary tin selenide K1-xSn5-xBi11+xSe22

Silver colored ribbon-like crystals of K1-xSn5-xBi11+xSe22 (x approximate to 0.33) were prepared by direct combination of K2Se, Bi2Se3, Sn and Se at 800 degrees C. A structure determination was carried out for K0.66Sn4.82Bi11.18Se22. 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)Se-6 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 K0.66Sn4.82Bi11.18Se22 at room temperature reveal an electrical conductivity of 450 S cm(-1) and a thermopower of -43 mu V 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. K0.66Sn4.82Bi11.18Se22 melts congruently at 680 degrees C.