The research team led by the Associate Professor GENG Huiyuan from School of Materials Science and Engineering have published their research results online entitled Filling-Fraction Fluctuation Leading to Glasslike Ultralow Thermal Conductivity in Caged Skutterudites in “Physical Review Letters”. This article is selected as the current cover of Letters. REN Wei, a 2016 doctor of HIT, is the first author. The research results provide an effective and universal mechanism for improving the thermoelectric properties of thermoelectric materials.
Caged compounds have many excellent physical properties and uses, such as thermoelectric and superconducting properties. Also, they can become topological insulators. Among caged compounds, caged skutterudites as the phonon-glass electron-crystal materials have excellent thermoelectric properties. Therefore, the materials have great potential applications in the field of deep space exploration, solar thermal power generation, industrial waste heat and exhaust heat recovery and such like. However, the lattice’s thermal conductivity is still far away from disorder limit, thus indicating that there is still much room for the thermoelectric properties of caged skutterudites to be improved.
Based on the the first principle calculation and experimental research, the research first discovered and then directly observed the uneven distribution of filling atoms in caged skutterudites, namely filling-fraction fluctuation. Also, the research results show that the perturbation effect and nanocrystallization form the effective scattering only for the low frequency phonon and caged skutterudites which are lacking an effective scattering mechanism for medium and high frequency phonon. The filling-fraction fluctuation leads to different scales of strain field in the lattice. The quantitative calculation of phonon transport demonstrates that the strain field forms effective scattering for medium and high frequency phonons. By using the filling-fraction fluctuation, the lattice thermal conductivity of caged skutterudites can be reduced to the disorder limit. The discovery and utilization of this mechanism will provide the theoretical basis and experimental basis for releasing the potential of the phonon-glass electron-crystal of caged compounds, which will greatly stimulate the development of thermoelectric materials of caged compounds.
Both the Associate Professor GENG Huiyuan and the Professor ZHANG Lixia are the corresponding authors of this article. GENG is responsible for the theoretical model of the project and the main part of the experimental design and ZHANG for the characterization analysis of microstructure in this article. The project is completed with the support of research funds from HIT Hundred Talents Program and the State Key Laboratory of advanced welding and joining.
The article link: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.245901
The journal link: https://journals.aps.org/prl/issues/118/24