Issue 6, 2016

Hierarchical thermoelectrics: crystal grain boundaries as scalable phonon scatterers


Thermoelectric materials are strategically valuable for sustainable development, as they allow for the generation of electrical energy from wasted heat. In recent years several strategies have demonstrated some efficiency in improving thermoelectric properties. Dopants affect carrier concentration, while thermal conductivity can be influenced by alloying and nanostructuring. Features at the nanoscale positively contribute to scattering phonons, however those with long mean free paths remain difficult to alter. Here we use the concept of hierarchical nano-grains to demonstrate thermal conductivity reduction in rocksalt lead chalcogenides. We demonstrate that grains can be obtained by taking advantage of the reconstructions along the phase transition path that connects the rocksalt structure to its high-pressure form. Since grain features naturally change as a function of size, they impact thermal conductivity over different length scales. To understand this effect we use a combination of advanced molecular dynamics techniques to engineer grains and to evaluate thermal conductivity in PbSe. By affecting grain morphologies only, i.e. at constant chemistry, two distinct effects emerge: the lattice thermal conductivity is significantly lowered with respect to the perfect crystal, and its temperature dependence is markedly suppressed. This is due to an increased scattering of low-frequency phonons by grain boundaries over different size scales. Along this line we propose a viable process to produce hierarchical thermoelectric materials by applying pressure via a mechanical load or a shockwave as a novel paradigm for material design.

Graphical abstract: Hierarchical thermoelectrics: crystal grain boundaries as scalable phonon scatterers

Article information

Article type
05 Aug 2015
14 Jan 2016
First published
15 Jan 2016
This article is Open Access
Creative Commons BY license

Nanoscale, 2016,8, 3729-3738

Author version available

Hierarchical thermoelectrics: crystal grain boundaries as scalable phonon scatterers

D. Selli, S. E. Boulfelfel, P. Schapotschnikow, D. Donadio and S. Leoni, Nanoscale, 2016, 8, 3729 DOI: 10.1039/C5NR05279C

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