Abstract
Most crystalline materials follow the guidelines of T−1 temperature-dependent lattice thermal conductivity (κL) at elevated temperatures. Here, we observe a weak temperature dependence of κL 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 3rd-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 κL in thermoelectrics.
Highlights
The study of thermal conductivity has been driven by the increasing concern on both intriguing physical phenomena and powerful technical applications [1]
Since the possible influence from electron-phonon interaction or off-diagonal contribution has been excluded, here, we focus on the variations of 2nd-order and 3rd-order interatomic force constant (IFC) and related physics to explore the origin of the weak temperature-dependent κL
300 K, as 2nd-order shown in Table S1. and 3rd-order IFCs, By we find that 2nd-order IFC related group velocity and scattering phase space have limited impact on κL, while 3rdorder IFC related anharmonicity plays a significant role
Summary
The study of thermal conductivity has been driven by the increasing concern on both intriguing physical phenomena and powerful technical applications [1]. The thermal conductivity in most crystalline materials consists of the lattice thermal conductivity (κL) and the electronic component (κe), which is related to the electrical conductivity (σ) through the Wiedemann-Franz law, κe = LσT, where L is the Lorenz number and T is the temperature. High thermal conductivity materials such as diamond and silicon are investigated in the area of thermal management of electronics. Research conductivity materials like Zintl phases [2, 3], skutterudites [4, 5], half-Heuslers [6, 7], and materials with chemical bond hierarchy [8,9,10] are widely used in high-performance thermoelectric energy conversion. The heat capacity Cv, the phonon velocity vg, and the relaxation time τ make contributions for κL [1] in the phonon gas model according to κL
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
