Abstract
The electronic and thermoelectric properties of Bi2Te3, PbBi2Te4 and PbBi4Te7 were examined on the basis of density functional theory (DFT) calculations and thermoelectric transport property measurements. The layered phase PbBi4Te7 is composed of the slabs forming the layered phases Bi2Te3 and PbBi2Te4. The electronic structure of PbBi4Te7 around the valence band maximum and conduction band minimum exhibits those of Bi2Te3 and PbBi2Te4. The band gap of PbBi4Te7 lies in between those of Bi2Te3 and PbBi2Te4, and the density of states of PbBi4Te7 is well approximated by the sum of those of Bi2Te3 and PbBi2Te4. In terms of the carrier concentration, the carrier mobility, the carrier lifetime, the electrical conductivity normalized to the carrier lifetime, and the effective mass, the layered phases Bi2Te3, PbBi4Te7 and PbBi2Te4 form a group of thermoelectrics, which have the structures composed of several different slabs and whose thermoelectric properties are approximated by the average of those of the constituent slabs. We propose to use the term “LEGO thermoelectrics” to describe such a family of thermoelectric materials that operate in a desired temperature range and possess predictable thermoelectric properties.
Highlights
Over the past several decades, thermoelectric materials have been extensively studied because of their ability to convert heat into electricity and their potential use in generating primary power and recovering waste heat.[1,2,3] Since their discovery in the 1950s, Bi2Te3 and PbTe are still the best thermoelectric materials around room temperature and in the medium temperature range, respectively, and have been widely used in thermoelectric modules.[4,5,6] It has been a challenging task to find more efficient thermoelectric materials
The conduction and valence bands is very similar to those of Bi2Te3 and PbBi2Te4. This finding prompted us to consider a new class of mixed-slab thermoelectrics whose thermoelectric properties are approximated by the average of those of the constituent slabs
In what follows we show that Bi2Te3, PbBi2Te4 and PbBi4Te7 are the first examples of LEGO thermoelectrics
Summary
Efforts made to improve the thermoelectric properties on Bi2Te3 and PbTe systems can be grouped into either enhancing the power factor S2σ8–18 (e.g., optimizing the carrier density, band engineering, using quantum confinement effects, and electron energy filtering) or reducing the lattice thermal conductivity[19,20,21,22,23] (e.g., the nanostructuring and all-scale hierarchical architecturing). Layered materials are interesting in that mixing different layers can improve thermoelectric properties[24,25,26,27] by increasing the power factor S2σ (via a change in the band gap and carrier density) and/or by reducing the lattice thermal conductivity κlat (via phonon scattering at the interfaces between different layers). The conduction and valence bands is very similar to those of Bi2Te3 and PbBi2Te4 This finding prompted us to consider a new class of mixed-slab thermoelectrics whose thermoelectric properties are approximated by the average of those of the constituent slabs. In what follows we show that Bi2Te3, PbBi2Te4 and PbBi4Te7 are the first examples of LEGO thermoelectrics
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