# Thermoelectrics: scattering heat-carrying phonons at every length scale

> A length-scale ladder for thermoelectric materials: waste heat enters, and the phonons that carry it are scattered by atomic disorder and anharmonic bonds, by nanoscale precipitates and by mesoscale grain boundaries before a thermoelectric module turns heat into electricity. Record figures of merit from SnSe crystals, hierarchical PbTe–SrTe and nanocrystalline BiSbTe run along the bottom.

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- Updated: 2026-10-14
- Category: Materials graphical abstracts
- Method: Graphical abstract
- Starting materials: Waste heat carried through a solid by phonons
- Product: A thermoelectric module that turns heat directly into electricity
- Key result: ZT 2.6 ± 0.3 at 923 K, SnSe b axis (Zhao et al. 2014); ZT ≈ 2.2 at 915 K, PbTe–4 mol% SrTe (Biswas et al. 2012); ZT 1.4 at 100 °C, nanocrystalline BiSbTe, after ≈ 1 for 50 years (Poudel et al. 2008)
- Figure: 1920 × 1080 px, 334 editable layers (2 generated objects with settings)

## Steps

1. **Waste heat**: About two-thirds of all used energy is lost as waste heat; thermoelectrics convert heat and electricity directly and reversibly (Biswas et al. 2012; Zhao et al. 2014)
2. **Atomic scale**: Atomic-scale lattice disorder scatters phonons; in SnSe, anharmonic and anisotropic bonding gives a lattice thermal conductivity of only 0.23 W m⁻¹ K⁻¹ at 973 K (Biswas et al. 2012; Zhao et al. 2014)
3. **Nanoscale**: Endotaxial SrTe nanoprecipitates (4 mol%) in PbTe scatter a large part of the phonon spectrum (Biswas et al. 2012)
4. **Mesoscale**: Grain boundaries made by powder processing and spark plasma sintering scatter long-mean-free-path phonons; in nanocrystalline BiSbTe, grain boundaries and defects lowered the thermal conductivity (Biswas et al. 2012; Poudel et al. 2008)
5. **Module**: Lower lattice thermal conductivity raises ZT, which governs the Carnot efficiency of heat-to-electricity conversion (Biswas et al. 2012; Snyder & Toberer 2008)

## Uses

- Graphical abstracts on thermoelectric materials
- Talks on phonon engineering and waste-heat recovery
- Teaching how nanostructuring lowers thermal conductivity

## References

1. Biswas et al., “High-performance bulk thermoelectrics with all-scale hierarchical architectures”, Nature 2012. https://doi.org/10.1038/nature11439 (primary)
2. Zhao et al., “Ultralow thermal conductivity and high thermoelectric figure of merit in SnSe crystals”, Nature 2014. https://doi.org/10.1038/nature13184 (primary)
3. Poudel et al., “High-thermoelectric performance of nanostructured bismuth antimony telluride bulk alloys”, Science 2008. https://doi.org/10.1126/science.1156446 (primary)
4. Snyder & Toberer, “Complex thermoelectric materials”, Nat. Mater. 2008. https://doi.org/10.1038/nmat2090 (review)

Credit: Drawn by LabCanvas after Biswas et al., Nature 2012 (doi:10.1038/nature11439); Zhao et al., Nature 2014 (doi:10.1038/nature13184); Poudel et al., Science 2008 (doi:10.1126/science.1156446); Snyder & Toberer, Nat. Mater. 2008 (doi:10.1038/nmat2090).

## Questions

**What does the “Thermoelectrics: scattering heat-carrying phonons at every length scale” template show?** A length-scale ladder for thermoelectric materials: waste heat enters, and the phonons that carry it are scattered by atomic disorder and anharmonic bonds, by nanoscale precipitates and by mesoscale grain boundaries before a thermoelectric module turns heat into electricity. Record figures of merit from SnSe crystals, hierarchical PbTe–SrTe and nanocrystalline BiSbTe run along the bottom.

**What are the steps shown in “Thermoelectrics: scattering heat-carrying phonons at every length scale”?** 1. Waste heat: About two-thirds of all used energy is lost as waste heat; thermoelectrics convert heat and electricity directly and reversibly (Biswas et al. 2012; Zhao et al. 2014). 2. Atomic scale: Atomic-scale lattice disorder scatters phonons; in SnSe, anharmonic and anisotropic bonding gives a lattice thermal conductivity of only 0.23 W m⁻¹ K⁻¹ at 973 K (Biswas et al. 2012; Zhao et al. 2014). 3. Nanoscale: Endotaxial SrTe nanoprecipitates (4 mol%) in PbTe scatter a large part of the phonon spectrum (Biswas et al. 2012). 4. Mesoscale: Grain boundaries made by powder processing and spark plasma sintering scatter long-mean-free-path phonons; in nanocrystalline BiSbTe, grain boundaries and defects lowered the thermal conductivity (Biswas et al. 2012; Poudel et al. 2008). 5. Module: Lower lattice thermal conductivity raises ZT, which governs the Carnot efficiency of heat-to-electricity conversion (Biswas et al. 2012; Snyder & Toberer 2008).

**What are the starting materials and the product?** Starting materials: Waste heat carried through a solid by phonons. Product: A thermoelectric module that turns heat directly into electricity.

**Which papers is “Thermoelectrics: scattering heat-carrying phonons at every length scale” based on?** Biswas et al., “High-performance bulk thermoelectrics with all-scale hierarchical architectures”, Nature 2012 (doi:10.1038/nature11439); Zhao et al., “Ultralow thermal conductivity and high thermoelectric figure of merit in SnSe crystals”, Nature 2014 (doi:10.1038/nature13184); Poudel et al., “High-thermoelectric performance of nanostructured bismuth antimony telluride bulk alloys”, Science 2008 (doi:10.1126/science.1156446); Snyder & Toberer, “Complex thermoelectric materials”, Nat. Mater. 2008 (doi:10.1038/nmat2090).

**Can I edit the “Thermoelectrics: scattering heat-carrying phonons at every length scale” template?** Yes. Open it in the LabCanvas editor: all 334 layers are editable, including 2 generated objects (structures, plots, equipment) with their own settings. Change the text, colours and layout, then export PNG, TIFF, SVG or PDF.

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