Controlling the heat transport in thermoelectric materials Jonathan Skelton 1 , J. M. Flitcroft 1 , I. Pallikara 1 , J. Cen 1,3 , J. Tang, 1 , B. Wei 1 , J. M. Frost 2,4 , L. D. Whalley 2,5 and A. Walsh 2,6 1 University of Manchester, UK, 2 Department of Chemistry, University of Bath, UK, 3 Department of Chemistry, University College London, UK, 4 Department of Chemistry, Imperial College London, UK, 5 Department of Mathematics, Physics and Electrical Engineering, Northumbria University, UK, 6 Department of Materials, Imperial College London,UK Around 60 % of the energy used globally is wasted as heat, 1 with clear implications for climate change. Thermoelectric (TE) power can address this by recycling waste heat to electricity, harnessing the Seebeck effect in a thermoelectric material to extract energy from a temperature gradient. Thermoelectric generators (TEGs) are established in the aerospace industry and have potential applications at scales from IoT devices, to automobile engines, to repurposing decommissioned oil rigs as geothermal power plants. 2 An ideal thermoelectric material requires a high Seebeck coefficient and electrical conductivity and a low thermal conductivity. 2,3 However, compared to the electrical properties the heat transport through the lattice vibrations (phonons) is less well understood, and less is known about how to control it. The lattice thermal conductivity can be modelled using techniques such as the single-mode relaxation-time approximation, 3 and theoretical calculations have proven valuable for understanding the low thermal conductivity in flagship TEs such as PbTe and SnSe. 4-6 This talk will build on these success to discuss how insight from modelling studies can be used to suggest structural modifications to control the heat transport in thermoelectric materials. The constant relaxation-time approximation (CRTA) analysis 7,8 allows differences in thermal conductivity to be attributed quantitatively to the phonon group velocities, which depend on the atomic masses and the chemical bond strength, and the phonon lifetimes, which depend on anharmonic phonon-phonon interactions. In materials with large group velocities the thermal transport can be suppressed by alloying, as in e.g. Sn(S 1- x Se x ), 8 or by chemical substitution with "discordant" dopants. 9 In materials with long lifetimes, introducing loosely-bound "rattler" ions, such as in CoSb 3 , can reduce the thermal conductivity through "resonant scattering" of the heat- carrying modes. 7 While this has yet to be explored in depth, calculations on the hybrid perovskite (CH 3 NH 3 )PbI 3 suggest that small-molecule rattlers may be particularly effective. 10 References
1. Firth, Zhang and Yang, Appl. Energy 235 , 1314 ( 2019 ) 2. Freer and Powell, J. Mater. Chem. C 8 , 441 ( 2020 ) 3. Tan, Zhao and Kanatzidis, Chem. Rev. 116 ( 19 ), 12123 ( 2016 ) 4. Delaire et al. , Nature Mater. 10 , 614 ( 2011 ) 5. Li et al. , Nature Phys. 11 , 1063 ( 2015 ) 6. Skelton et al. , Phys. Rev. Lett. 117 , 075502 ( 2016 ) 7. Tang and Skelton, J. Phys.: Condens. Matter 33 , 164002 ( 2021 ) 8. Skelton, J. Mater. Chem. C 9 , 11772 ( 2021 ) 9. Xie et al. , J. Am. Chem. Soc. 141 ( 47 ), 18900 ( 2019 ) 10. Gold-Parker et al. , Proc. Natl. Acad. Sci. USA 115 ( 47 ), 11905 ( 2018 )
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