The compounds A1+xM′3-2xBi7+xSe14 and A1-xM′3-xBi11+xSe20 (A = K, Rb, Cs; M′ = Sn, Pb) were discovered from reactions involving A2Se, Bi2Se3, M′, and Se at 760 °C. The single-crystal structures reveal that A1+xM′3-2xBi7+xSe14 are isostructural to K2.5Bi8.5Se14 whereas A1-xM′3-xBi11+xSe20 adopt a new structure type. Both compound types belong to the homologous series Am[M6Se8]m [M5+nSe9+n] (M = di- and trivalent metal), whose characteristics are three-dimensional anionic frameworks with tunnels filled with alkali ions. The building units are derived from different sections of the NACI lattice, perpendicular to the  (NaCl111-type) and  (NaCl100-type) directions, respectively, with dimensions and shapes defined by m and n. The structures of A1+xM′3-2xBi7+xSe14 (m = 2, n = 3) and A1-xM′3-xBi11+xSe20 (m = 1, n = 3) exhibit the same type of stepshaped NACl111-type layer but differ in the size of the NaCl100-type unit. In both structures, the Bi and Sn (Pb) atoms are extensively disordered over the metal sites of the chalcogenide network. The physicochemical and charge transport properties of A1+xM′3-2xBi7+xSe14 and A1-xM′3-xBi11+xSe20 (A = K, Rb, Cs; M′ = Sn, Pb) are reported.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry