Decoupled charge and heat transport in Fe2VAl composite thermoelectrics with topological-insulating grain boundary networks
Fabian Garmroudi, Illia Serhiienko, Michael Parzer, Sanyukta Ghosh, Paweł Ziółkowski, Gregor Oppitz, Nguyễn Duy Hiếu, Cédric Bourgès, Yuya Hattori, Alexander Riss, Sebastian Steyrer, Gerda Rogl, P. Rogl, Erhard Schafler, Naoyuki Kawamoto, Eckhard Müller, E. Bauer, Johannes de Boor, Takao Mori
Abstract
Abstract Decoupling charge and heat transport is essential for optimizing thermoelectric materials. Strategies to inhibit lattice-driven heat transport, however, also compromise carrier mobility, limiting the performance of most thermoelectrics, including Fe 2 VAl Heusler compounds. Here, we demonstrate an innovative approach, which bypasses this tradeoff: via liquid-phase sintering, we incorporate the archetypal topological insulator Bi 1− x Sb x between Fe 2 V 0.95 Ta 0.1 Al 0.95 grains. Structural investigations alongside extensive thermoelectric and magneto-transport measurements reveal distinct modifications in the microstructure, a reduced lattice thermal conductivity and a simultaneously enhanced carrier mobility arising from topologically protected charge transport along the grain boundaries. This yields a huge performance boost, resulting in one of the highest figure of merits among both half- and full-Heusler compounds, z ≈ 1.6 × 10 −3 K −1 ( z T ≈ 0.5) at 295 K. Our findings highlight the potential of topological-insulating secondary phases to decouple charge and heat transport and call for more advanced theoretical studies of multiphase composites.