Assembling thermoelectric materials into units can transform the thermal difference to electrical energy or vice versa – electrical current to cooling. But effective utilisation requires that the material to supply a high voltage and have good electrical conductivity and low thermal conductivity.
New research goes towards explaining exactly why some thermoelectric materials can have the desired low thermal conductivity without degrading the electrical properties. This can be crucial for the conversion of wasted heat, for example, from vehicle exhaust emissions. Leading car manufacturers are now working to develop this possibility and the first models are close to production. This technology is expected to give the cars considerably improved fuel economy, according to Bo B Iversen, Professor at iNANO at the University of Århus. The new research can also contribute to the development of new cooling methods, therby avoiding the need to use greenhouse gases, such as R-134a. The researchers have studied one of the most promising thermoelectric materials in the group of clathrates, which create crystals full of ‘nano-cages’. By placing a heavy atom in each nano-cage, it is possible to reduce the ability of the crystals to conduct heat. Until now it was thought that it was the random movement of heavy atoms in the cages that was the cause of poor thermal conductivity, but this has been shown not to be true, according to Asger B Abrahamsen, senior scientist at Risø-DTU. The researchers have used the technique of neutron scattering, which gives them opportunity to look into the material and see the atoms’ movements. The data shows that it is in fact the atoms’ shared pattern of movement that determines the properties of these thermoelectric materials. This discovery is significant for the design of new materials that utilise energy better.
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