Attaining high mid-temperature performance in (Bi,Sb)2Te3 thermoelectric materials via synergistic optimization

Abstract

For decades, zone-melted Bi 2 Te 3 -based alloys have been the most widely used thermoelectric materials with an optimal operation regime near room temperature. However, the abundant waste heat in the mid-temperature range poses a challenge; namely, how and to what extent the service temperature of Bi 2 Te 3 -based alloys can be upshifted to the mid-temperature regime. We report herein a synergistic optimization procedure for Indium doping and hot deformation that combines intrinsic point defect engineering, band structure engineering and multiscale microstructuring. Indium doping modulated the intrinsic point defects, broadened the band gap and thus suppressed the detrimental bipolar effect in the mid-temperature regime; in addition, hot deformation treatment rendered a multiscale microstructure favorable for phonon scattering and the donor-like effect helped optimize the carrier concentration. As a result, a peak value of zT of~1.4 was attained at 500 K, with a state-of-the-art average zT av of~1.3 between 400 and 600 K in Bi 0.3 Sb 1.625 In 0.075 Te 3 . These results demonstrate the efficacy of the multiple synergies that can also be applied to optimize other thermoelectric materials. INTRODUCTIONThermoelectricity is the simplest technology for direct heat-toelectricity power generation. Thermoelectric (TE) devices are all solid state, without rotation parts or working fluids, and are thus easy to miniaturize. These modular characteristics make TE devices reliable, durable and easy to use in tandem with other energy conversion technologies. 1,2 The energy conversion efficiency of a TE device is primarily determined by the TE material's dimensionless figure of merit, defined as zT = α 2 σT/κ, where α is the Seebeck coefficient, σ is the electrical conductivity, κ is the total thermal conductivity (including the lattice contribution κ L and the carrier contribution κ e ) and T is the absolute temperature. 2 zT is generally a function of temperature whereas waste heat is the energy source for TE power generation. It is useful to compare the optimal operation temperature ('service temperature') of state-of-the-art TE materials and the temperature range in which most of the waste heat is produced. State-of-the-art TE materials have their best zT values (those between 1 and 2) in different temperature regimes; for example, Bi 2 Te 3 works best near room temperature, 3,4 whereas PbTe, Mg 2 Si 1-x Sn x , Half-Heusler compounds and filled skutterudites generally reach their best performance above 600 K. [5][6][7][8][9][10][11][12][13][14] There is a conspicuous lack of high-performance TE materials between 400 and 600 K, the

Compromise and Synergy in High‐Efficiency Thermoelectric Materials

“…Moreover, new techniques also make it possible to prepare materials with desired composition and structure, and thus the electrical and thermal transport can be manipulated more independently and precisely. After years of efforts, synergistic optimization for high zT s has been accomplished successfully in a few TE materials, such as FeNbSb‐based HH compounds, Pb(Te,Se)‐based alloys, and Bi 2 Te 3 ‐based alloys, etc.…”

Intrinsically Low Thermal Conductivity in BiSbSe3: A Promising Thermoelectric Material with Multiple Conduction Bands

“…To clearly confirm the structure of (Br‐doped) BiSbSe 3 , compared with the two end terminal members of Bi 2 Se 3 and Sb 2 Se 3 , we employed electron diffraction and scanning transmission electron microscopy (STEM) imaging techniques . The Bi 2 Se 3 exhibits five‐layer structure (Se (1) BiSe (2) BiSe (1) ) as Bi 2 Te 3 , as shown in Figure a,b. Through 50% alloying with Sb on Bi site, the BiSbSe 3 totally changes to the structure of Sb 2 Se 3 without any precipitates.…”

Flexible Thermoelectric Materials and Generators: Challenges and Innovations

“…A few inorganic TE materials exhibit a superior zT of ≈1 at room temperature . However, their applications as FTE materials are restricted by their inherent rigidity.…”