Crystal Structure and Thermoelectric Properties of the ^7,7L Lillianite Homologue Pb₆Bi₂Se₉

Abstract

PbBiSe, 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, N = N = 7, where N is the number of edge-sharing [Pb/Bi]Se octahedra along the central diagonal. In the crystal structure, adjacent layers are arranged along the c-axis such that bridging bicapped trigonal prisms, PbSe, are located on a pseudomirror plane parallel to (001). Therefore, PbBiSe corresponds to a L 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.

Inelastic neutron scattering study of the lattice dynamics of the homologous compounds (PbSe)5(Bi2Se3)3m (m = 1, 2 and 3)

“…The inherent disorder present in their unit cell makes these compounds an interesting area of research for designing materials with low lattice thermal conductivity, , for thermoelectric applications or for searching for novel compounds with topologically non-trivial electronic band structure. [4][5][6][7][8][9][10][11][12][13] Both topological surface states and interesting thermoelectric properties were indeed evidenced in the series of homologous compounds (PbSe)5(Bi2Se3)3m ( Our results show that the overall features of the GVDOS are only weakly affected upon increasing m. The inelastic response is dominated at low energies by vibrational modes centred near 4.8 meV likely associated with the thermal motion of the Pb atoms. For all compounds, the temperature response of the GVDOS is indicative of a quasi-harmonic behaviour with no evident signs of anharmonicity beyond that related to thermal expansion.…”

High carrier mobility and ultralow thermal conductivity in the synthetic layered superlattice Sn4Bi10Se19

“…These include, A m [M 1+l Se 2+l ] 2m [M 2l+n Se 2+3l+n ] (A = K, Rb, Cs and M = Sn, Pb) where l, m, and n represent the size of various structural building units; 32,33 34 and the lillianite, Pb NÀ1À2x Bi 2+x-Ag x S N+2 , 35 and the Pb NÀ1 Bi 2 Se N+2 36 homologous series, where N = (N1 + N2)/2 representing the average of the number of edgesharing octahedra running across the central diagonal of the two NaCl-type building units forming the crystal structure. Among these homologous families of complex mixed-metal chalcogenides, phases belonging to the pseudo binary PbSe -Bi 2 Se 3 phase diagram, such as ternary compounds consisting of varying ratios of (PbSe) m (Bi 2 Se 3 ) n layers [37][38][39][40][41] and Pb NÀ1 Bi 2 Se N+2 , 36 at 300 K) and a moderate figure of merit, ZT B 0.25 at 650 K. 43 Following the example of the (PbSe) w (Bi 2 Se 3 ) t family mentioned above, we have recently embarked on the search for new Earthabundant ternary thermoelectric materials for mid-temperature range applications within the (SnSe) w (Bi 2 Se 3 ) t system. It is anticipated that in such a system the integration at the atomic scale of structural features from SnSe and Bi 2 Se 3 phases, which are promising thermoelectric materials suitable for applications at high temperatures and below room temperature, respectively, can create compounds suitable for mid-range (300 K to 700 K) power generation application.…”

Low-temperature transport properties of n-type layered homologous compounds Bi8−xSbxSe7

“…[21][22][23][24][25] These high thermoelectric performances stem from the high degeneracy of the conduction bands that yield high thermopower values, combined with highly-anharmonic phonon branches that strongly limit the heat transport to values well below 1 W m -1 K -1 around 300 K. [21][22][23][24][25] Homologous compounds possess similar high structural complexity and significant chemical flexibility, making them another excellent research area to design novel thermoelectric materials. [26][27][28][29][30][31] The crystal structure of these compounds is built from one or several types of slabs, the thicknesses and stacking sequence of which expand in one or several spatial directions by regular increments. The chemical composition of a homologous series can be rationalized by integer numbers, which can help to predict novel compounds.…”

“…26 Several families of homologous compounds naturally exist as minerals, some of them, such as the cannizzarite, pavonite or lillianite, have been shown to exhibit interesting thermoelectric properties. [28][29][30][31][32][33] Among them, the tetradymite series stand out due to the fact that the above-mentioned Bi2Te3-based compounds belong to this broad family of compounds. In the Bi-Se sub-system, thirteen binary compounds with varying Bi-to-Se ratio have been identified so far, spanning the phase space from elemental semi-metallic Bi to semiconducting Bi2Se3.…”