Scientists use neutrons to look at boost thermoelectric efficiency

ORNL Instrument Scientist Clarina de la Cruz used the HB-2A Neutron Powder Diffractometer at the High Flux Isotope Reactor to analyze a cobalt-doped thermoelectric material boasting a record increase in room-temperature performance. Credit: ORNL/Genevieve Martin

Neutron facilities at Oak Ridge National Laboratory are aiding scientists in research to boost the power and efficiency of thermoelectric materials. These performance increases could enable more cost-effective and practical uses for thermoelectrics, with wider industry adoption, to improve fuel economy in vehicles, make power plants more efficient, and advance body heat–powered technologies for watches and smartphones.

Thermoelectric materials, typically metal compounds, can convert heat to electricity and vice versa in the presence of a temperature gradient, making them ideal for applications in waste heat recovery.

Thermoelectrics could capitalize on enormous amounts of unused waste heat produced by industrial operations, fossil-fuel power generation, commercial buildings, vehicles, and even people by converting that “lost” heat into usable energy. But so far their application has been limited to add-on technologies due to their low efficiency compared with conventional forms of energy generation.

To reach benchmarks set for standalone thermo-powered devices, scientists are now looking deeper—down to the atoms—into promising materials and methods to raise efficiency scores.

Working with a magnesium-antimony–based material, an international research team led by University of Houston physicist Zhifeng Ren has demonstrated a substantial increase in the alloy’s power factor, or total energy output, with a technique called defect engineering. By substituting cobalt atoms at strategic sites, researchers altered the pathway for electrons in a way that significantly improved their mobility. Neutron analysis performed at ORNL played a key role in verifying the method’s success.

The results, published in Proceedings of the National Academy of Sciences, are commercially relevant with a figure of merit, or ZT value, of ~1.7 achieved in thermoelectric efficiency. Most significant is the material’s increase in power factor at room temperature with a record jump from 5 to 13 μW·cm−1·K−2 that more than doubled the material’s total energy output.

The resulting power factor is far from the record of 106 at room temperature reached by Ren and others previously, but the method of boosting it could be applied to superior materials—particularly those with a power factor already above 100—to make the most efficient thermoelectrics even better.

Read more: Scientists use neutrons to look at boost in thermoelectric efficiency

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