Publication Date:
2015-08-08
Description:
We report the synthesis and high thermoelectric properties of Zr 3 Ni 3 Sb 4 -Hf 3 Ni 3 Sb 4 solid solutions and Zr 3 Ni 3 Sb 4 -Zr 3 Pt 3 Sb 4 solid solutions. Ternary Zintl phases Zr 3 Ni 3 Sb 4 , Hf 3 Ni 3 Sb 4 , and Zr 3 Pt 3 Sb 4 are narrow-gap semiconductors (a bandgap E g ≃ 200 meV in the case of Zr 3 Ni 3 Sb 4 ) with low thermal conductivity (4.3 W/mK in the case of Zr 3 Ni 3 Sb 4 at 300 K). An electronic state calculation of these ternary Zintl phases indicates that the valence bands have a 6-valley or 12-valley structure, providing a high density-of-state effective mass, whereas the conduction bands have low effective mass, resulting in high mobility. Because of these electronic properties that enhance the β factor and the low thermal conductivity due to complex crystal structure and more alloying scattering, high ZT values were obtained for the p-type Zr 3 Ni 2.3 Pt 0.6 Co 0.1 Sb 4 ( ZT = 0.65 at 760 K) and the n-type Zr 2 HfNi 2.7 Cu 0.3 Sb 4 ( ZT = 0.56 at 670 K). We found that Pt-substitution improves the high-temperature thermoelectric performance above 600 K owing to band-gap widening and thermal conductivity reduction in alloying of the p-type Zr 3 (Ni,Pt) 2.9 Co 0.1 Sb 4 solid solutions. In the case of n-type (Zr,Hf) 3 Ni 2.7 Cu 0.3 Sb 4 solid solutions, we observed that Hf-substitution reduces κ ph without negatively affecting carrier mobility.
Print ISSN:
0021-8979
Electronic ISSN:
1089-7550
Topics:
Physics
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