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Thermoelectric properties of n-type half-Heusler NbCoSn with heavy-element Pt substitution

: Serrano-Sánchez, Federico; Luo, Ting; Yu, Junjie; Xie, Wenjie; Le, Congcong; Auffermann, Gudrun; Weidenkaff, Anke; Zhu, Tiejun; Zhao, Xinbing; Alonso, José A.; Gault, Baptiste; Felser, Claudia; Fu, Chenguang

Fulltext ()

Journal of materials chemistry. A, Materials for energy and sustainability 8 (2020), No.29, pp.14822-14828
ISSN: 2050-7488
ISSN: 2050-7496
Journal Article, Electronic Publication
Fraunhofer IWKS ()
annealing; chemical element; cobalt alloys; computational studies; crystal lattices; electric power factor; electronic structure; grain boundary; grain boundary scattering; Half-Heusler compound; hall mobility; high electrical power; hole mobility; iron alloys; lattice thermal conductivity; niobium alloy; platinum compounds; structural characterization; ternary alloy; thermal conductivity; thermoelectric equipment; thermo-electric materials; thermoelectric properties; thermoelectricity; tin alloys; Zircaloy

Half-Heusler compounds with a valence electron count of 18, including ZrNiSn, ZrCoSb, and NbFeSb, are good thermoelectric materials owing to favorable electronic structures. Previous computational studies had predicted a high electrical power factor in another half-Heusler compound NbCoSn, but it has not been extensively investigated experimentally. Herein, the synthesis, structural characterization, and thermoelectric properties of the heavy-element Pt-substituted NbCoSn compounds are reported. Pt is found to be an effective substitute enabling the optimization of electrical power factor and simultaneously leading to a strong point defect scattering of phonons and the suppression of lattice thermal conductivity. Post-annealing significantly improves the carrier mobility, which is ascribed to the decreased grain boundary scattering of electrons. As a result, a maximum power factor of ∼3.4 mW m−1 K−2 is obtained at 600 K. In conjunction with the reduced lattice thermal conductivity, a maximum figure of merit zT of ∼0.6 is achieved at 773 K for the post-annealed NbCo0.95Pt0.05Sn, an increase of 100% compared to that of NbCoSn. This work highlights the important roles that the dopant element and microstructure play in the thermoelectric properties of half-Heusler compounds.