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January 18, 2011

Nanocrystals of rock salt into lead telluride create breakthrough thermoelectric

Nature Chemistry - Strained endotaxial nanostructures with high thermoelectric figure of merit The crystallographic alignment of SrTe and PbTe lattices decouples phonon and electron transport and this allows the system to reach a thermoelectric figure of merit of 1.7 at ~800 K. The material exhibits a high thermoelectric figure of merit that is expected to enable 14 percent of heat waste to electricity, a scientific first

Researchers at Northwestern University have placed nanocrystals of rock salt into lead telluride, creating a material that can harness electricity from heat-generating items such as vehicle exhaust systems, industrial processes and equipment and sun light more efficiently than scientists have seen in the past.

Thermoelectrics with higher conversion efficiency will have more impact on smaller applications. Cars and refridgerators and smaller devices will benefit more. Larger generators have higher conversion efficiencies of heat to electricity. Thermoelectric conversion efficiency increases with higher temperature differential.

ZT (the figure of merit) for the temperature ranges (700K) for best TE materials (mid-2010) have been about 1.4 and need to be closer to 3.0 to reach the efficiency goals requested by DOE.



Thermoelectric materials can directly generate electrical power from waste heat but the challenge is in designing efficient, stable and inexpensive systems. Nanostructuring in bulk materials dramatically reduces the thermal conductivity but simultaneously increases the charge carrier scattering, which has a detrimental effect on the carrier mobility. We have experimentally achieved concurrent phonon blocking and charge transmitting via the endotaxial placement of nanocrystals in a thermoelectric material host. Endotaxially arranged SrTe nanocrystals at concentrations as low as 2% were incorporated in a PbTe matrix doped with Na2Te. This effectively inhibits the heat flow in the system but does not affect the hole mobility, allowing a large power factor to be achieved. The crystallographic alignment of SrTe and PbTe lattices decouples phonon and electron transport and this allows the system to reach a thermoelectric figure of merit of 1.7 at ~800 K.

9 pages of supplemental material



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