Maximizing phonon scattering efficiency by Cu2Se alloying in AgCuTe thermoelectric materials

Nanoengineering has always been an effective way to optimize thermoelectric materials. Multi-layered nanostructures can maximize the phonon scattering efficiency and greatly reduce the thermal conductivity, thus improving the thermoelectric performance. In this work, multi-layered nanostructures are constructed in AgCuTe by alloying Cu2Se, which strongly scatters full-wavelength phonons and achieves a new low thermal conductivity at 723 K. High-resolution transmission electron microscopy shows that additional phase boundaries, multiple Moiré fringes and regular nanophases are formed after alloying Cu2Se. Moiré fringes form high density dislocations and strong stress fields in AgCuTe, which can greatly scatter multi-wavelength phonons. In addition, the Cu+ ions generated after the dissolution of a small amount of Cu2Se participate in the electrical transport, which optimizes the electrical performance. In the end, the AgCuTe-1%Cu2Se sample achieves the lowest thermal conductivity of ∼0.45 W m−1 K−1 at 723 K, which is much lower than the average level of published AgCuTe-based materials. At the same time, between 523 K and 723 K, the average ZT ∼ 1.13 of AgCuTe-1%Cu2Se reached the leading level. This work provides a new strategy for further reducing the thermal conductivity of AgCuTe-based materials.