First-Principles Study on Lattice Dynamics and Thermal Conductivity of Thermoelectric Intermetallics Fe3Al2Si3

Abstract

Thermoelectric materials have been expected as a critical underlying technology for developing an autonomous power generation system driven at near room temperature. For this sake, Fe3Al2Si3 intermetallic compound is a promising candidate, though its high lattice thermal conductivity is a bottleneck toward practical applications. Herein, we have performed the first-principles calculations to clarify the microscopic mechanism of thermal transport and establish effective ways to reduce the lattice thermal conductivity of Fe3Al2Si3. Our calculations show that the lowest-lying optical mode has a significant contribution from Al atom vibration. It should correspond to large thermal displacements Al atoms. However, these behaviors do not directly cause an increase of the 3-phonon scattering rate. The calculated lattice thermal conductivity shows a typical temperature dependence and moderate magnitude. From the calculated thermal conductivity spectrum and cumulative thermal conductivity, we can see that there is much room to reduce the lattice thermal conductivity. We can expect that heavy-element doping on Al site and controlling fine microstructure are effective strategies to decrease the lattice thermal conductivity. This work suggests useful information to manipulate the thermal transport of Fe3Al2Si3, which will make this material closer to practical use.

Fe–Al–Si Thermoelectric (FAST) Materials and Modules: Diffusion Couple and Machine-Learning-Assisted Materials Development

“…The minimum lattice thermal conductivity (κ min ≈ 1.3 W m –1 K –1 at room temperature) of FAST materials was calculated by the model proposed by Cahill et al Because the values of σ for FAST materials are distributed in the range of 400–600 Ω –1 cm –1 , the κ electron will be ∼0.4 W m –1 K –1 at room temperature, as estimated from the Wiedemann–Franz law. Thus, the minimum total thermal conductivity (κ = κ electron + κ min ) is estimated to be 1.7 W m –1 K –1 at room temperature, indicating that there is room for further reduction of κ total (and κ phonon ) for FAST materials through phonon engineering . Shiota et al succeeded in reducing the κ total (3.5–4.5 W m –1 K –1 at room temperature) by elemental substitution .…”