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.