Novel insights into lattice thermal transport in nanocrystalline Mg 3 Sb 2 from first principles: the crucial role of higher-order phonon scattering.

Zintl phase Mg ₃ Sb ₂ , which has ultra-low thermal conductivity, is a promising anisotropic thermoelectric material. It is worth noting that the prediction and experiment value of lattice thermal conductivity ( κ ) maintain a remarkable difference, troubling the development and application. Thus, we firstly included the four-phonon scattering processes effect and performed the Peierls-Boltzmann transport equation (PBTE) combined with the first-principles lattice dynamics to study the lattice thermal transport in Mg ₃ Sb ₂ . The results showed that our theoretically predicted κ is consistent with the experimentally measured, breaking through the limitations of the traditional calculation methods. The prominent four-phonon scatterings decreased phonon lifetime, leading to the κ of Mg ₃ Sb ₂ at 300 K from 2.45 (2.58) W m ^-1 K ^-1 to 1.94 (2.19) W m ^-1 K ^-1 along the in (cross)-plane directions, respectively, and calculation accuracy increased by 20%. This study successfully explains the lattice thermal transport behind mechanism in Mg ₃ Sb ₂ and implies guidance to advance the prediction accuracy of thermoelectric materials.