Realization of Band Convergence in p-Type TiCoSb Half-Heusler Alloy Significantly Enhances the Thermoelectric Performance - Université de Lorraine Access content directly
Journal Articles ACS Applied Materials & Interfaces Year : 2023

Realization of Band Convergence in p-Type TiCoSb Half-Heusler Alloy Significantly Enhances the Thermoelectric Performance

Abstract

Band engineering is a promising approach that proved successful in enhancing the thermoelectric performance of several families of thermoelectric materials. Here, we show how this mechanism can be induced in the p-type TiCoSb half-Heusler (HH) compound to effectively improve the Seebeck coefficient. Both the Pisarenko plot and electronic band structure calculations demonstrate that this enhancement is due to increased density-of-states effective mass resulting from the convergence of two valence band maxima. Our calculations evidence that the valence band maximum of TiCoSb lying at the Γ point exhibits a small energy difference of 51 meV with respect to the valence band edge at the L point. Experimentally, this energy offset can be tuned by both Fe and Sn substitutions on the Co and Sb site, respectively. An Sn doping level as low as x = 0.03 is sufficient to drive more than ~ 100 % increase in the power factor at room temperature. Further, defects at various length-scales, that include point defects, edge dislocations and nano- sized grains evidenced by electron microscopy (FESEM and HRTEM), results in enhanced phonon scattering which substantially reduces the lattice thermal conductivity to ~ 4.2 W m-1 K-1 at 873 K. Combined with enhanced power factor, a peak ZT value of ~ 0.4 was achieved at 873 K in TiCo0.85Fe0.15Sb0.97Sn0.03. In addition, the micro-hardness and fracture toughness were found to be enhanced for all the synthesized samples, falling in the range of 8.3 – 8.6 GPa and 1.8 – 2 MPa m-1/2, respectively. Our results highlight how the combination of band convergence and microstructure engineering in the HH alloy TiCoSb is effective for tuning its thermoelectric performance.
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Dates and versions

hal-03969250 , version 1 (20-02-2023)

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Ajay Kumar Verma, Kishor Kumar Johari, Paritosh Dubey, Durgesh Kumar Sharma, Sudhir Kumar, et al.. Realization of Band Convergence in p-Type TiCoSb Half-Heusler Alloy Significantly Enhances the Thermoelectric Performance. ACS Applied Materials & Interfaces, 2023, 15 (1), pp.942-952. ⟨10.1021/acsami.2c16721⟩. ⟨hal-03969250⟩
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