title: Crystal Structure and Thermoelectric Properties of the7,7L Lillianite Homologue Pb6Bi2Se9.
abstract: Pb6Bi2Se9, the selenium analogue of heyrovsyite, crystallizes in the orthorhombic space group Cmcm (#63) with a = 4.257(1) Å, b = 14.105(3) Å, and c = 32.412(7) Å at 300 K. Its crystal structure consists of two NaCl-type layers, A and B, with equal thickness, N1= N2= 7, where N is the number of edge-sharing [Pb/Bi]Se6octahedra along the central diagonal. In the crystal structure, adjacent layers are arranged along the c-axis such that bridging bicapped trigonal prisms, PbSe8, are located on a pseudomirror plane parallel to (001). Therefore, Pb6Bi2Se9corresponds to a7,7L member of the lillianite homologous series. Electronic transport measurements indicate that the compound is a heavily doped narrow band gap n-type semiconductor, with electrical conductivity and thermopower values of 350 S/cm and -53 μV/K at 300 K. Interestingly, the compound exhibits a moderately low thermal conductivity, ∼1.1 W/mK, in the whole temperature range, owing to its complex crystal structure, which enables strong phonon scattering at the twin boundaries between adjacent NaCl-type layers A and B. The dimensionless figure of merit, ZT, increases with temperature to 0.25 at 673 K.
authors.affiliation: Laboratory for Emerging Energy and Electronic Materials, Department of Materials Science and Engineering, and ‡Department of Physics, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Joseph
authors.initials: J
authors.lastname: Casamento
authors.affiliation: Laboratory for Emerging Energy and Electronic Materials, Department of Materials Science and Engineering, and ‡Department of Physics, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Juan S
authors.initials: JS
authors.lastname: Lopez
authors.affiliation: Laboratory for Emerging Energy and Electronic Materials, Department of Materials Science and Engineering, and ‡Department of Physics, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Moroz
authors.affiliation: Laboratory for Emerging Energy and Electronic Materials, Department of Materials Science and Engineering, and ‡Department of Physics, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Alan
authors.initials: A
authors.lastname: Olvera
authors.affiliation: Laboratory for Emerging Energy and Electronic Materials, Department of Materials Science and Engineering, and ‡Department of Physics, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Honore
authors.initials: H
authors.lastname: Djieutedjeu
authors.affiliation: Laboratory for Emerging Energy and Electronic Materials, Department of Materials Science and Engineering, and ‡Department of Physics, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Alexander
authors.initials: A
authors.lastname: Page
authors.affiliation: Laboratory for Emerging Energy and Electronic Materials, Department of Materials Science and Engineering, and ‡Department of Physics, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Ctirad
authors.initials: C
authors.lastname: Uher
authors.affiliation: Laboratory for Emerging Energy and Electronic Materials, Department of Materials Science and Engineering, and ‡Department of Physics, University of Michigan , Ann Arbor, Michigan 48109, United States.
authors.forename: Pierre F P
authors.identifier: http://orcid.org/0000-0002-2422-9550
authors.initials: PF
authors.lastname: Poudeu