Introduction
Thermoelectric materials convert temperature gradients directly into electricity (and vice versa) with no moving parts, no noise, and long service life. They are used in industrial waste-heat recovery, automotive exhaust energy harvesting, deep-space radioisotope generators (RTGs), and solid-state cooling. This guide helps procurement and R&D engineers navigate material systems, key metrics, and selection logic.
Key Metric: The Dimensionless Figure of Merit (ZT)
Performance is defined by ZT = S²σT / κ, where S is the Seebeck coefficient, σ the electrical conductivity, κ the thermal conductivity, and T the absolute temperature. Higher ZT means efficiency closer to the Carnot limit. Also evaluate the power factor (S²σ), mechanical strength, and thermal stability.
- ZT ≈ 1: mainstream commercial level (e.g., Bi₂Te₃)
- ZT ≈ 1.5–2: advanced nanostructured / band-engineered materials
- ZT > 2: laboratory stage, not yet mass-produced
Material Systems by Temperature Range
| System | Range | Typical ZT | Applications |
|---|---|---|---|
| Bismuth Telluride (Bi₂Te₃) | RT–250°C | 0.8–1.2 | Solid-state cooling, wearables |
| Lead Telluride (PbTe) | 250–550°C | 1.0–1.8 | Automotive & mid-temp industrial |
| Silicon-Germanium (SiGe) | 600–1000°C | 0.8–1.0 | Deep-space RTGs |
| Skutterudites | 400–600°C | 1.0–1.4 | Automotive mid-high temp |
| Half-Heusler alloys | 400–700°C | 1.0–1.5 | High-temp, high-strength duty |
Selection Decision Points
- Match the temperature range first. Define hot/cold-side temperatures, then pick the material. Use segmented/stacked designs for wide gradients.
- Cost & resource risk. Tellurium (Te) and germanium (Ge) are scarce and expensive; Half-Heusler and Mg₃Sb₂-based systems attract interest for element abundance.
- Environmental compliance. Lead-based PbTe faces RoHS restrictions in some markets; assess alternatives for consumer exports.
- Thermo-mechanical reliability. Check CTE matching, thermal-cycling fatigue, and diffusion-barrier interface design.
Procurement & Acceptance
- Require full temperature-dependent curves for ZT, Seebeck, conductivity, and thermal conductivity — not single-point values.
- Verify device-level specs: max output power, internal resistance, thermal-cycle lifetime (thousands of cycles).
- Confirm bonding process and diffusion barriers to prevent high-temperature interface degradation.
- Batch consistency: request ZT variation ranges across multiple lots and QC reports.
Conclusion
Thermoelectric selection is a balance of temperature range, ZT, cost, and reliability. As band engineering, nanostructuring, and lead-/tellurium-free systems mature, waste-heat recovery economics keep improving. Always base decisions on device-level measured data rather than peak single-point ZT.
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