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Issue 17, 2020
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Na-doping enables both dislocations and holes in EuMg2Sb2 for thermoelectric enhancements

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Abstract

A high conduction band degeneracy (Nv = 6) leads to an extraordinary figure of merit (zT) in n-type Mg3Sb2 thermoelectrics, while the p-type ones show a much inferior zT due to its lower Nv of only 1 owing to the large energy offset (ΔE ∼ 0.4 eV) between the two valence bands. The derivatives of Mg3Sb2, ternary AB2C2 (A = Eu, Yb, Ca, Sr, Ba; B = Mg, Zn, Cd; C = Sb, Bi) Zintls, show a similar valence band structure but with a much smaller ΔE of <0.2 eV, leading to potential convergence of both valence bands for a high overall Nv of 3. This band feature promotes AB2C2 ternaries to be potential p-type thermoelectrics matching with n-type Mg3Sb2 for efficient thermoelectric applications, thus motivating the current work focusing on p-type EuMg2Sb2 thermoelectrics. Interestingly, Na-doping at the Eu site is found to be particularly effective for creating dense in-grain dislocations, which results in a remarkable reduction in lattice thermal conductivity to ∼0.5 W m−1 K−1. Moreover, Na-doping increases the hole concentration up to 6.0 × 1019 cm−3, leading to an effective involvement of multiple transporting valence bands. The synergistic effects of dense dislocations and multi-band transport, both enabled by Na-doping, led EuMg2Sb2 to show the highest zT among known doped p-type ternary AMg2C2 Zintl thermoelectrics.

Graphical abstract: Na-doping enables both dislocations and holes in EuMg2Sb2 for thermoelectric enhancements

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Article information


Submitted
21 Feb 2020
Accepted
03 Apr 2020
First published
03 Apr 2020

J. Mater. Chem. A, 2020,8, 8345-8351
Article type
Paper

Na-doping enables both dislocations and holes in EuMg2Sb2 for thermoelectric enhancements

C. Sun, W. Li, X. Shi, Z. Bu, P. Nan, Y. Li, B. Ge and Y. Pei, J. Mater. Chem. A, 2020, 8, 8345
DOI: 10.1039/D0TA02081H

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