Machine-Learning-Assisted Development and Theoretical Consideration for the Al<sub>2</sub>Fe<sub>3</sub>Si<sub>3</sub> Thermoelectric Material

Published on 2019-03-18T15:21:17Z (GMT) by
Chemical composition alteration is a general strategy to optimize the thermoelectric properties of a thermoelectric material to achieve high-efficiency conversion of waste heat into electricity. Recent studies show that the Al<sub>2</sub>Fe<sub>3</sub>Si<sub>3</sub> intermetallic compound with a relatively high power factor of ∼700 μW m<sup>–1</sup> K<sup>–2</sup> at 400 K is promising for applications in low-cost and nontoxic thermoelectric devices. To accelerate the exploration of the thermoelectric properties of this material in a mid-temperature range and to enhance its power factor, a machine-learning method was employed herein to assist the synthesis of off-stoichiometric samples (namely, Al<sub>23.5+<i>x</i></sub>Fe<sub>36.5</sub>Si<sub>40–<i>x</i></sub>) of the Al<sub>2</sub>Fe<sub>3</sub>Si<sub>3</sub> compound by tuning the Al/Si ratio. The optimal Al/Si ratio for a high power factor in the mid-temperature range was found rapidly and efficiently, and the optimal ratio of the sample at <i>x</i> = 0.9 was found to increase the power factor at ∼510 K by about 40% with respect to that of the initial sample at <i>x</i> = 0.0. The possible mechanism for the enhanced power factor is discussed in terms of the precipitations of the metallic secondary phases in the Al<sub>23.5+<i>x</i></sub>Fe<sub>36.5</sub>Si<sub>40–<i>x</i></sub> samples. Furthermore, the maximum achievable thermal conductivity of Al<sub>2</sub>Fe<sub>3</sub>Si<sub>3</sub> estimated by the Slack model is ∼10 W m<sup>–1</sup> K<sup>–1</sup> at the Debye temperature. An avoided-crossing behavior of the acoustic and the low-lying optical modes along several crystallographic directions is found in the phonon dispersion of Al<sub>2</sub>Fe<sub>3</sub>Si<sub>3</sub> calculated by ab initio density functional theory method. These preliminary results suggest that Al<sub>2</sub>Fe<sub>3</sub>Si<sub>3</sub> can have a low thermal conductivity. The calculated formation energies of point defects suggest that the antisite defects between Al and Si are likely to cause the Al and Si off-stoichiometries in Al<sub>2</sub>Fe<sub>3</sub>Si<sub>3</sub>. The theoretically obtained insight provides additional information for the further understanding of Al<sub>2</sub>Fe<sub>3</sub>Si<sub>3</sub>.

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Hou, Zhufeng; Takagiwa, Yoshiki; Shinohara, Yoshikazu; Xu, Yibin; Tsuda, Koji (2019): Machine-Learning-Assisted

Development and Theoretical Consideration for the Al2Fe3Si3 Thermoelectric Material. ACS Publications. Collection.