2019/03/21 by Xia, Yi, Ozoliņš, Vidvuds
#FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci)
paper · doi:10.48550/arxiv.1903.08800
Crystalline compounds exhibiting low-frequency rattling phonons constitute an important class of high-performance thermoelectrics owning to their intrinsically very low lattice thermal conductivity (κl). Theoretical approach that is capable of revealing the physical origin and accurately predicting κl is of particular interest, which, however, still remains an outstanding challenge. In this study, we perform a case study of lattice dynamics and thermal transport properties of Ag6Ge10P12, which has recently been identified as a high-performance thermoelectric phosphide due to low κl, arising from rattling vibrations associated with Ag6 clusters. Analysis within a first-principles-based lattice-dynamics framework based on self-consistent phonon theory reveals a strong temperature dependence of rattling phonons due to high-order anharmonic interactions. Anharmonic hardening of the rattling optical modes has a strong effect on the lifetimes of heat-carrying acoustic phonons by decreasing the rate of three-phonon combination processes. This mechanism results in a significant increase in κl and changes its temperature dependence to 1/T0.64.