Maximizing phonon scattering efficiency by Cu2Se alloying in AgCuTe thermoelectric materials

Abstract

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.