Thermoelectric generators have the potential to convert heat to electrical power in a range of industrial sectors.

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This highlight discusses recent trends in the search for new high-efficiency thermoelectric materials. Thermoelectric materials offer considerable attractions in the pursuit of a more efficient use of existing energy resources, as they may be used to construct power-generation devices that allow useful electrical power to be extracted from otherwise waste heat. Here, we focus on the significant enhancements in thermoelectric performance that have been achieved through nanostructuring. The principal factor behind the improved performance appears to be increased phonon scattering at interfaces. This results in a substantial reduction in the lattice contribution to thermal conductivity, a low value of which is a key requirement for improved thermoelectric performance.

Understanding the underlying mechanisms that suppress thermal conduction in solids is of paramount importance for the targeted design of materials for thermal management and thermoelectric energy conversion applications. Bismuth copper oxychalcogenides, BiOCuQ (Q = Se, Te), are highly crystalline thermoelectric materials with an unusually low lattice thermal conductivity of ∼0.5 Wm(-1) K(-1), a value normally found in amorphous materials. Here we unveil the origin of the unusual thermal transport properties of these phases. First principles calculations of the vibrational properties combined with analysis of in-situ neutron diffraction data, demonstrate that weak bonding of copper atoms within the structure leads to an unexpected vibrational mode at low frequencies, which is likely to be a major contributor to the low thermal conductivity of these materials. In addition, we show that anharmonicity and the large Grüneisen parameter in these oxychalcogenides are mainly related to the low frequency copper vibrations, rather than to the Bi(3+) lone pairs.

Tetrahedrites are promising p-type thermoelectric materials for energy recovery. We present here the first investigation of the structure and thermoelectric properties of copper-rich tetrahedrites, Cu 12+x Sb 4 S 13 (0 < x ≤ 2.0). At room temperature, all samples with x > 0 consist of two tetrahedrite phases. In situ neutron diffraction data demonstrate that on heating, the two tetrahedrite phases coalesce into a single tetrahedrite phase at temperatures between 493 and 553 K and that this transition shows marked hysteresis on cooling. Our structural data indicate that copper ions become mobile above 393 K. Marked changes in the temperature dependence of the electrical and thermal transport properties of the copper-rich phases occur at the onset of copper mobility. Excess copper leads to a significant reduction in the total thermal conductivity, which for the nominal composition Cu 14 Sb 4 S 13 reaches a value as low as 0.44 W m −1 K −1 at room temperature, and to thermoelectric properties consistent with phonon liquid electron crystal (PLEC) behavior.

The ability of thermoelectric devices to convert waste heat into useful electrical power has stimulated a remarkable growth in research into thermoelectric materials. There is however, growing recognition that limited reserves of tellurium together with the reduction in performance that occurs at elevated temperatures, places constraints on the widespread implementation of thermoelectric technology based on the current generation of telluridebased devices. Metal sulfides have attracted considerable attention as potential tellurium-free

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