Homologous Series of 2D Chalcogenides Cs-Ag-Bi-Q (Q = S, Se) with Ion-Exchange Properties.

Four new layered chalcogenides CsAgBiS, CsAgBiSe, CsAgBiS, and CsAgBiSe are described. CsAgBiS and CsAgBiSe are isostructural and have a hexagonal P6/mmc space group; their structures consist of [Ag/Bi]Q (Q = S, Se) quintuple layers intercalated with disordered Cs cations. CsAgBiS also adopts a structure with the hexagonal P6/mmc space group and its structure has an [Ag/Bi]S layer intercalated with a Cs layer. CsAgBiS and CsAgBiS can be ascribed to a new homologous family A[MS] (m = 1, 2, 3···). CsAgBiSe is orthorhombic with Pnnm space group, and it is a new member of the A[MSe] homology with n = 6. The Cs ions in CsAgBiS and CsAgBiS can be exchanged with other cations, such as Ag, Cd, Co, Pb, and Zn forming new phases with tunable band gaps between 0.66 and 1.20 eV. CsAgBiS and CsAgBiS possess extremely low thermal conductivity (<0.6 W·m·K).