Enhanced thermoelectric performance of heavy-fermion YbAl3 via multi-scale microstructures

How to optimize the thermoelectric performance of heavy-fermion systems remains a key challenge due to the extremely high thermal conductivity rooted in the extraordinarily high electrical conductivity. Here we report a new approach to simultaneously optimize the electron and phonon transport properties of heavy-fermion YbAl3 by fabricating the multi-scale microstructures spanning from the atomic to nanometer to mesoscopic scales. We discover theoretically and experimentally that in YbAl3 the nanostructures with less than 30 nm in size and atomic-scale dislocations and Yb vacancies can simultaneously scatter electron and phonon and thus significantly decrease the electrical conductivity and electronic thermal conductivity, while other hierarchical microstructures from the nanometer to mesoscopic scales can effectively scatter phonons and remarkably decrease the lattice thermal conductivity. The highest thermoelectric figure of merit ZT reaches 0.4 at 300 K and increased by 74%, which is a new record for un-doped YbAl3. Our work demonstrates that the electron and phonon transport properties of heavy-fermion system can be simultaneously enhanced by the multi-scale microstructures. (C) 2017 Elsevier B.V. All rights reserved.