Violation of the T ^-1 Relationship in the Lattice Thermal Conductivity of Mg₃Sb₂ with Locally Asymmetric Vibrations.

ABSTRACT: Most crystalline materials follow the guidelines of T ^-1 temperature-dependent lattice thermal conductivity (? _L ) at elevated temperatures. Here, we observe a weak temperature dependence of ? _L in Mg₃Sb₂, T ^-0.48 from theory and T ^-0.57 from measurements, based on a comprehensive study combining ab initio molecular dynamics calculations and experimental measurements on single crystal Mg₃Sb₂. These results can be understood in terms of the so-called "phonon renormalization" effects due to the strong temperature dependence of the interatomic force constants (IFCs). The increasing temperature leads to the frequency upshifting for those low-frequency phonons dominating heat transport, and more importantly, the phonon-phonon interactions are weakened. In-depth analysis reveals that the phenomenon is closely related to the temperature-induced asymmetric movements of Mg atoms within MgSb₄ tetrahedron. With increasing temperature, these Mg atoms tend to locate at the areas with relatively low force in the force profile, leading to reduced effective 3^rd-order IFCs. The locally asymmetrical atomic movements at elevated temperatures can be further treated as an indicator of temperature-induced variations of IFCs and thus relatively strong phonon renormalization. The present work sheds light on the fundamental origins of anomalous temperature dependence of ? _L in thermoelectrics.

SUBMITTER: Zhu Y 

PROVIDER: S-EPMC7877392 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature