Structure and thermoelectric properties of the silver lead bismuth selenides Ag5Pb9Bi19Se40 and AgPb3Bi7Se14Electronic supplementary information (ESI) available: Details on the syntheses; tables of atomic parameters for the single-crystal structure refinements; a figure of the evolution of lattice parameters and displacement parameters with temperature; results of Rietveld refinement; and additional HRTEM images. See DOI: 10.1039/c8dt01895b

• Main Authors: Heinke, Frank, Nietschke, Frederik, Fraunhofer, Christina, Dovgaliuk, Iurii, Schiller, Jordana, Oeckler, Oliver
• Format: Article
• Language: English
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c8dt01895b

In the system Ag/Pb/Bi/Se, two new thermoelectric phases derived from lillianite (Pb 3 Bi 2 S 6 ) have been characterized. The crystal structures correspond to the 8,8 L- and 5,5 L-types, respectively, both in the space group Cmcm . The room-temperature unit-cell parameters of 8,8 L-Ag 5 Pb 9 Bi 19 Se 40 are a = 4.2151(8) Å, b = 13.951(3) Å and c = 35.284(7) Å and those of 5,5 L-AgPb 3 Bi 7 Se 14 are a = 4.2337(8) Å, b = 13.864(2) Å and c = 24.653(3) Å. The temperature-dependent evolution of the lattice parameters of Ag 5 Pb 9 Bi 19 Se 40 becomes steeper at temperatures above 300 °C and hints at the mobility of Ag + ions. Samples containing both phases exhibit thermoelectric figures of merit up to ZT = 0.23 at 250 °C. HRTEM investigations on such samples showed well-ordered areas of the lillianite-like phases separated by large slabs that exhibit a high concentration of defects and may compensate for lattice misfits between the lillianite-type phases. Two new lillianite-like phases in the system Ag/Pb/Bi/Se are characterized by pronounced disorder and promising ZT values up to 0.23.