4.7 Article

n-Type thermoelectric properties of a hexagonal SiGe polymorph superior to a cubic SiGe

Journal

JOURNAL OF ALLOYS AND COMPOUNDS
Volume 874, Issue -, Pages -

Publisher

ELSEVIER SCIENCE SA
DOI: 10.1016/j.jallcom.2021.160007

Keywords

SiGe; First-principles study; Boltzmann transport equation; Polymorph; Thermoelectric

Funding

  1. Creative Materials Discovery Program through the National Research Foundation of Korea (NRF) - Ministry of Science and ICT [NRF2017M3D1A1039287]
  2. Global Frontier Program through the Global Frontier Hybrid Interface Materials (GFHIM) of the National Research Foundation of Korea (NRF) - Ministry of Science and ICT [2013M3A6B1078882]

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This study explores the superior thermoelectric properties of a hexagonal SiGe compound compared to its cubic counterpart, revealing that the differences in electronic band structure and phonon vibrational modes are the main factors contributing to the enhanced performance. Based on these findings, hexagonal SiGe is proposed as a promising material for highly active n-type thermoelectric applications.
The crystal structure of a material dictates many of its properties. This study focuses on a SiGe compound with a hexagonal crystal system that demonstrates superior thermoelectric properties than that of its conventional cubic polymorph. Using first-principles density functional theory (DFT) calculations combined with the semi-classical Boltzmann transport equation (BTE), we clearly elucidate the underlying mechan-isms that cause the enhanced thermoelectric performance. The hexagonal SiGe compound shows different folding behavior of the electronic band structure, leading to dissimilar density of states and enhanced Seebeck coefficient, compared to the cubic counterpart. Moreover, the phonon vibrational modes of the hexagonal SiGe shorten the phonon lifetime due to the different lattice symmetry. Based on the results, we propose hexagonal SiGe as a promising material for a highly active n-type thermoelectric material with a figure of merit that is twice of its cubic analogue. Our approach demonstrates an attractive method for substantially enhancing conventional material properties without a complicated or expensive process for developing a novel material. (c) 2021 Elsevier B.V. All rights reserved.

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