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Title: Enhanced thermoelectric performance of Mg 2Si 1-xSn x codoped with Bi and Cr

Magnesium silicides are favorable thermoelectric materials considering resource abundance and cost. Chromium (Cr) doping in magnesium silicides has not yet been explored. Using first-principles calculations, we have studied the stability of Mg 2Si with chromium (1.85, 3.7, 5.55, and 6.25% Cr) and tin (12.5 and 50% Sn). Three Mg 2Si compounds doped with Sn, (Sn + Bi), and (Sn + Bi + Cr) are used to explain doping effects on thermoelectric performance. Notably, Cr behaves nonmagnetically for ≤2%Cr, after which ferromagnetic ordering is favored (≤12.96% Cr), despite its elemental antiferromagnetic state. With alloying of Sn (70.4%), Mg 2Si remains an indirect-band-gap semiconductor, but adding small amounts of Bi (3.7%) increases the carrier concentration such that electrons occupy conduction bands, making it a degenerate semiconductor. Mg 2Si 0.296Sn 0.666Bi 0.037 is found to give the highest thermoelectric figure of merit (ZT) and power factor (PF) at 700 K, i.e., 1.75 and 7.04 mWm –1K –2, respectively. Adding small %Cr decreases ZT and PF to 0.78 and 4.33 mWm –1K –2, respectively. Such a degradation in thermoelectric (TE) performance is attributed to two factors: (i) uniform doping acting as an electron acceptor, decreasing conduction, and (ii) the loss of low-lying conduction bandmore » degeneracy with doping, decreasing the Seebeck coefficients. In conclusion, a study of configurations of Cr doping suggests that Cr has a tendency to form clusters inside the lattice, which play a crucial role in tuning the magnetic and TE performance of doped Mg 2Si compounds.« less
Authors:
 [1] ;  [2] ;  [1]
  1. Indian Institute of Technology, Mumbai (India)
  2. Ames Lab. and Iowa State Univ., Ames, IA (United States)
Publication Date:
Report Number(s):
IS-J-9770
Journal ID: ISSN 2469-9950; PRBMDO
Grant/Contract Number:
AC02-07CH11358
Type:
Accepted Manuscript
Journal Name:
Physical Review B
Additional Journal Information:
Journal Volume: 98; Journal Issue: 11; Journal ID: ISSN 2469-9950
Publisher:
American Physical Society (APS)
Research Org:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE
OSTI Identifier:
1477198
Alternate Identifier(s):
OSTI ID: 1471800

Vikram, FNU, Johnson, Duane D., and Alam, Aftab. Enhanced thermoelectric performance of Mg2Si1-xSnx codoped with Bi and Cr. United States: N. p., Web. doi:10.1103/PhysRevB.98.115204.
Vikram, FNU, Johnson, Duane D., & Alam, Aftab. Enhanced thermoelectric performance of Mg2Si1-xSnx codoped with Bi and Cr. United States. doi:10.1103/PhysRevB.98.115204.
Vikram, FNU, Johnson, Duane D., and Alam, Aftab. 2018. "Enhanced thermoelectric performance of Mg2Si1-xSnx codoped with Bi and Cr". United States. doi:10.1103/PhysRevB.98.115204.
@article{osti_1477198,
title = {Enhanced thermoelectric performance of Mg2Si1-xSnx codoped with Bi and Cr},
author = {Vikram, FNU and Johnson, Duane D. and Alam, Aftab},
abstractNote = {Magnesium silicides are favorable thermoelectric materials considering resource abundance and cost. Chromium (Cr) doping in magnesium silicides has not yet been explored. Using first-principles calculations, we have studied the stability of Mg2Si with chromium (1.85, 3.7, 5.55, and 6.25% Cr) and tin (12.5 and 50% Sn). Three Mg2Si compounds doped with Sn, (Sn + Bi), and (Sn + Bi + Cr) are used to explain doping effects on thermoelectric performance. Notably, Cr behaves nonmagnetically for ≤2%Cr, after which ferromagnetic ordering is favored (≤12.96% Cr), despite its elemental antiferromagnetic state. With alloying of Sn (70.4%), Mg2Si remains an indirect-band-gap semiconductor, but adding small amounts of Bi (3.7%) increases the carrier concentration such that electrons occupy conduction bands, making it a degenerate semiconductor. Mg2Si0.296Sn0.666Bi0.037 is found to give the highest thermoelectric figure of merit (ZT) and power factor (PF) at 700 K, i.e., 1.75 and 7.04 mWm–1K–2, respectively. Adding small %Cr decreases ZT and PF to 0.78 and 4.33 mWm–1K–2, respectively. Such a degradation in thermoelectric (TE) performance is attributed to two factors: (i) uniform doping acting as an electron acceptor, decreasing conduction, and (ii) the loss of low-lying conduction band degeneracy with doping, decreasing the Seebeck coefficients. In conclusion, a study of configurations of Cr doping suggests that Cr has a tendency to form clusters inside the lattice, which play a crucial role in tuning the magnetic and TE performance of doped Mg2Si compounds.},
doi = {10.1103/PhysRevB.98.115204},
journal = {Physical Review B},
number = 11,
volume = 98,
place = {United States},
year = {2018},
month = {9}
}

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