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Preparation, thermoelectric properties, and crystal structure of boron-doped Mg2Si single crystals

Authors :
Kei Hayashi
Wataru Saito
Kazuya Sugimoto
Kenji Ohoyama
Kouichi Hayashi
Naohisa Happo
Masahide Harada
Kenichi Oikawa
Yasuhiro Inamura
Yuzuru Miyazaki
Source :
AIP Advances, Vol 10, Iss 3, Pp 035115-035115-7 (2020)
Publication Year :
2020
Publisher :
AIP Publishing LLC, 2020.

Abstract

Mg2Si is a potential thermoelectric (TE) material that can directly convert waste energy into electricity. In expectation of improving its TE performance by increasing electron carrier concentration, the element boron (B) is doped in Mg2Si single crystals (SCs). Their detailed crystal structures are definitely determined by using white neutron holography and single-crystal x-ray diffraction (SC-XRD) measurements. The white neutron holography measurement proves that the doped B atom successfully substitutes for the Mg site. The SC-XRD measurement confirms the B-doping site and also reveals the presence of the defect of Si vacancy (VSi) in the B-doped Mg2Si SCs. The fraction of VSi increases with increasing B-doping concentration. In the case of B-doped Mg2Si polycrystals (PCs), VSi is absent; this difference between the SCs and PCs can be attributed to different preparation temperatures. Regarding TE properties, the electrical conductivity, σ, and the Seebeck coefficient, S, decreases and increases, respectively, due to the decrease in the electron carrier concentration, contrary to the expectation. The power factor of the B-doped Mg2Si SCs evaluated from σ and S does not increase but rather decreases by the B-doping. The tendencies of these TE properties can be explained by considering that the donor effect of the B atom is canceled by the acceptor effect of VSi for the B-doped Mg2Si SCs. This study demonstrates that the preparation condition of Mg2Si should be optimized to prevent the emergence of an unexpected point defect.

Subjects

Subjects :
Physics
QC1-999

Details

Language :
English
ISSN :
21583226
Volume :
10
Issue :
3
Database :
Directory of Open Access Journals
Journal :
AIP Advances
Publication Type :
Academic Journal
Accession number :
edsdoj.2d4e5e1af193427a992df5e94b245ef0
Document Type :
article
Full Text :
https://doi.org/10.1063/1.5143839