Lattice dynamics and lattice thermal conductivity of CrSi2 calculated from first principles and the phonon Boltzmann transport equation

• Published in: Journal of applied physics 2019-07, Vol.126 (2)
• Main Authors: Nakasawa, Hayato, Hayashi, Kei, Takamatsu, Tomohisa, Miyazaki, Yuzuru
• Format: Article
• Language: English
• Subjects: Anharmonicity; Applied physics; Boltzmann transport equation; Crystallites; Dependence; First principles; Heat conductivity; Heat transfer; Mathematical analysis; Phonons; Polycrystals; Power factor; Single crystals; Thermal conductivity; Transport equations
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.5096458

Efficiently decreasing the lattice thermal conductivity, κL, is one of the main concerns in the field of thermoelectrics (TE). Herein, we theoretically investigate κL for single-crystal and polycrystalline CrSi2 using first-principles and the phonon Boltzmann transport equation. Though CrSi2 is known as a potential TE material because of its reasonable power factor, controlling its κL remains as a challenge to be solved. In this study, we discuss how to decrease κL efficiently on the basis of the calculation. The phonon band structure and density of states are computed via harmonic calculation. In addition, the achievable lowest lattice thermal conductivity, κL0, and cumulative lattice thermal conductivity, κcum, are estimated using the Cahill model and anharmonic calculation, respectively. We predict κL0 for CrSi2 to be around 2.2Wm−1K−1 at 650 K, which suggests that CrSi2 is a potential TE material with high zT over 0.39 at 650 K. The phonon mean-free path dependence of κcum indicates that the critical crystallite size for decreasing κL for polycrystalline CrSi2 is 70 nm at 600 K. In addition, it is revealed that the crystallite size should be as small as 7 nm to decrease κL to half. These calculational findings offer useful insights into how to control κL for CrSi2.