Dramatically reduced lattice thermal conductivity of Mg_2Si thermoelectric material from nanotwinning
Guodong Li, Jiangang He, Qi An, Sergey I. Morozov, Shiqiang Hao, Pengcheng Zhai, Qingjie Zhang, William A. Goddard III, G. Jeffrey Snyder
Abstract
Tuning phonon transport to reduce the lattice thermal conductivity (κ_L) is crucial for advancing thermoelectrics (TEs). Traditional strategies on κ_L reduction focus on introducing scattering sources such as point defects, dislocations, and grain boundaries, that may degrade the electrical conductivity and Seebeck coefficient. We suggest here, a novel twin boundary (TB) strategy that can decrease the κ_L of Mg_2Si by ∼90%, but which may not degrade the electrical properties significantly. We validate this suggestion using density functional theory (DFT). We attribute the mechanism of TB induced κ_L reduction to (i) the lower phonon velocities and larger Grüneisen parameter, (ii) "rattling" of the Mg--Mg pair induced soft acoustic and optical modes, (iii) shorter phonon lifetime and higher phonon scattering rate. We predict that the size of nanotwinned structure should be controlled between 3 nm and 100 nm in the Mg2Si matrix for the most effective κ_L reduction. These results should be applicable for other TE or non TE energy materials with desired low thermal conductivity, suggesting rational designs of high-performance Mg_2Si TE materials with low κ_L for the energy conversion applications.
Group Members
Li, G., He, J., An, Q., Morozov, S. I., Hao, S., Zhai, P., Zhang, Q., III, W. A. G., & Snyder, G. J. (2019). Dramatically reduced lattice thermal conductivity of Mg_2Si thermoelectric material from nanotwinning. *Acta Materialia*, *169*, 9-14. https://doi.org/10.1016/j.actamat.2019.02.041