Low Thermal Conductivity in Single Crystalline Mg3Bi2 and Its Thermopower Enhanced by Electron‐Phonon Interaction

Abstract Promising thermoelectric materials are usually those of “phonon‐glass electron‐crystal” (PGEC) compounds, with low thermal conductivity and high carrier mobility. In metallic materials, strong electron‐phonon interaction usually causes an increase of Seebeck coefficient ( S ) at low temperature, due to an extra electrical current driven by heat‐carrying phonons, named phonon drag effect. Here, this study reports that single crystalline metallic Mg 3 Bi 2 has low lattice thermal conductivity of ≈0.49 W m −1 K −1 at 285 K, and corresponding mean free path of phonons ( L ph ) is ≈0.48 nm, with carrier mobility of ≈54.2 cm 2 V −1 s −1 around room temperature. It is found that S exhibits an increase as a “hump” ≈20 K, and phonon drag effect ( S ph ) contributes to ≈80%, significantly higher than diffusive electrons. Meanwhile, S ph is positively proportional to L ph , where coefficient of S ph / L ph is ≈4.6 × 10 2 µV K −1 µm −1 , twice that of CrSb 2 and FeSb 2 , and relative strength of electron‐phonon interaction is ≈0.12. The L ph ‐intercept of S ph / L ph approaches to ≈4.68 nm, where phonons can be strongly scattered before interacting with electrons, leading to a negligible phonon drag effect. The findings shed light on fundamental understanding of thermoelectric transport and exploring novel thermoelectric materials.