| Slide 2 34 % 26 % 19 % 18 % 3 % 1000 MW nuclear power plant: o 650 MW waste heat o 3 % ≈ 20 MW ≈ 50,000 homes 300-500 W from exhaust gases: o 2 % lower fuel consumption o 2.4 Mt reduction in CO2 Thermoelectric generators allow waste heat to be recovered as electricity TEGs with ~3 % energy recovery (𝑍𝑇 = 1) are considered industrially viable 1. Provisional UK greenhouse gas emissions national statistics (published June 2020) 2. EPSRC Thermoelectric Network Roadmap (2018)
- Seebeck coefficient 𝜎 - electrical conductivity 𝜅ele - electronic thermal conductivity 𝜅lat - lattice thermal conductivity G. Tan et al., Chem. Rev. 116 (19), 12123 (2016) Dr Jonathan Skelton MISE Finale Workshop June 2021 | Slide 3
094306 (2015) 𝜿latt (𝑇) = 1 𝑁𝑉0 𝜆 𝐶𝜆 (𝑇)𝒗𝜆 ⊗ 𝒗𝜆 𝜏𝜆 (𝑇) The simplest model for 𝜅latt is the relaxation time approximation (RTA) - a closed solution to the phonon Boltzmann transport equations Modal heat capacity Mode group velocity 𝜕𝜔λ 𝜕𝐪 Average over phonon modes λ Phonon MFP Mode lifetime 𝜏λ = 1 2Γλ 𝚲𝜆 𝑇 = 𝒗𝜆 𝜏𝜆 𝑇 Dr Jonathan Skelton MISE Finale Workshop June 2021 | Slide 7
Properties 1 10 100 1,000 10,000 1.000 0.875 0.750 0.625 0.500 0.375 0.250 0.125 0.000 Number of Structures Se Fraction Total Unique Dr Jonathan Skelton MISE Finale Workshop June 2021 | Slide 13
“Model 2”: 54.9 % ↓ “Model 3”: 59.4 % ↓ Expt: ~60-70 % ↓ Dr Jonathan Skelton MISE Finale Workshop June 2021 | Slide 22 J. M. Skelton, J. Mater. Chem. C (2021), DOI: 10.1039/D1TC02026A C.-C. Lin et al., Chem. Mater. 29 (12), 5344 (2017)
accurate predictions and useful insight into how the 𝜅latt of thermoelectric materials “works” The CRTA model separates the 𝜅latt of a material into harmonic (heat capacity/group velocity) and anharmonic (lifetime) components, and may be a useful metric for comparing different TE materials The 𝜅latt of SnS and SnSe are a balance of smaller group velocities and longer lifetimes in the selenide A theoretical model for the Snm (S1-x Sex )n system suggests: o close to ideal mixing behaviour; o volume variation in accordance with Vegard’s law; and o a predictable variation in the bandgap of Sn(S1-x Sex )2 with composition, covering the Shockley–Queisser limit Calculations predict a 40-60 % reduction in the 𝜅latt of the Sn(S0.1875 Se0.8125 ) compared to SnSe, which can be ascribed mainly to a “smearing” of the phonon dispersion and a consequent reduction in the mode group velocities Dr Jonathan Skelton MISE Finale Workshop June 2021 | Slide 23