Low Thermal Conductivity in Single Crystalline MgBi and Its Thermopower Enhanced by Electron-Phonon Interaction.

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 MgBi has low lattice thermal conductivity of ≈0.49 W m K at 285 K, and corresponding mean free path of phonons (L) is ≈0.48 nm, with carrier mobility of ≈54.2 cm V s around room temperature. It is found that S exhibits an increase as a "hump" ≈20 K, and phonon drag effect (S) contributes to ≈80%, significantly higher than diffusive electrons. Meanwhile, S is positively proportional to L, where coefficient of S/L is ≈4.6 × 10 µV K µm, twice that of CrSb and FeSb, and relative strength of electron-phonon interaction is ≈0.12. The L-intercept of S/L 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.