Compositional modulation is driven by aliovalent doping in n-type TiCoSb based half-Heuslers for tuning thermoelectric transport

Vishwakarma, Avinash; Chauhan, Nagendra S.; Bhardwaj, Ruchi; Johari, Kishor Kumar; Dhakate, Sanjay R.; Gahtori, Bhasker; Bathula, Sivaiah

doi:10.1016/j.intermet.2020.106914

Cited by 17 publications

(22 citation statements)

References 40 publications

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“…Interestingly, κ is significantly lower and varies marginally in the measured temperature range, which can be ascribed to the defect chemistry and alloy scattering supplemented by mass and strain fluctuation, all of which synergistically enhance phonon scattering. The measured values for pristine VCoSb − and TiCoSb − HH alloys are comparable to previous reports. Upon annealing, the occurrence of spinodal decompositions further lowers the κ significantly for a wide temperature range, which is comparable to the κ obtained in bulk nanostructured ternary HH alloys.…”

Section: Resultssupporting

confidence: 90%

“…As reported previously, , the synthesized VCoSb HH alloy also exhibits a relatively high μ H that has been related to the metallic characteristics arising from the presence of one electron in the conduction band. TiCoSb HH alloys show relatively lower n H and μ H , explaining their semiconducting properties and lower σ, consistent with previous reports on TiCoSb HH alloys. − Although a linear increase in n H with increasing VEC was observed for intermediate Ti 1– x V x CoSb HH alloys (0.25 < x < 0.75), a marginal change in μ H was observed, which is comparable to VCoSb HH, implying stronger carrier scattering at higher n H . Upon annealing, a higher μ H but reduced n H was measured for VCoSb, TiCoSb, and Ti 0.5 V 0.5 CoSb (Table ), which correlates with the lowering σ upon annealing.…”

Section: Resultssupporting

confidence: 90%

“…Figure c displays the temperature-dependent Seebeck coefficient ( S ) exhibiting negative values that indicate n-type conduction with electrons as majority charge carriers. As reported previously, − TiCoSb HH alloy demonstrates a remarkably high S ≈ 300 μV K –1 in the measured temperature range, while VCoSb HH alloy displays a relatively low S . For the as-sintered intermediate Ti 1– x V x CoSb HH alloys (0.25 < x < 0.75), S values are closely related to VCoSb and can be attributed to their high n H .…”

Section: Resultssupporting

confidence: 87%

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Low Lattice Thermal Conductivity in a Wider Temperature Range for Biphasic-Quaternary (Ti,V)CoSb Half-Heusler Alloys

Chauhan

Bhattacharjee

Maiti

et al. 2022

ACS Appl. Mater. Interfaces

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Intrinsically high lattice thermal conductivity has remained a major bottleneck for achieving a high thermoelectric figure of merit (zT) in state-of-the-art ternary half-Heusler (HH) alloys. In this work, we report a stable n-type biphasic-quaternary (Ti,V)CoSb HH alloy with a low lattice thermal conductivity κL ≈ 2 W m–1 K–1 within a wide temperature range (300–873 K), which is comparable to the reported nanostructured HH alloys. A solid-state transformation driven by spinodal decomposition upon annealing is observed in Ti0.5V0.5CoSb HH alloy, which remarkably enhances phonon scattering, while electrical properties correlate well with the altering electronic band structure and valence electron count (VEC). A maximum zT ≈ 0.4 (±0.05) at 873 K was attained by substantial lowering of κL and synergistic enhancement of the power factor. We perform first-principles density functional theory calculations to investigate the structure, stability, electronic structure, and transport properties of the synthesized alloy, which rationalize the reduction in the lattice thermal conductivity to the increase in anharmonicity due to the alloying. This study upholds the new possibilities of finding biphasic-quaternary HH compositions with intrinsically reduced κL for prospective thermoelectric applications.

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Section: Resultssupporting

confidence: 90%

Section: Resultssupporting

confidence: 90%

Section: Resultssupporting

confidence: 87%

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Low Lattice Thermal Conductivity in a Wider Temperature Range for Biphasic-Quaternary (Ti,V)CoSb Half-Heusler Alloys

Chauhan

Bhattacharjee

Maiti

et al. 2022

ACS Appl. Mater. Interfaces

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“…Figure 3 represents the change in 𝜖 and d with increasing Ni concentration. 𝜖 is negative, implies compressive-strain [18]. 𝜖 is minimum for x=0.02, whereas highest value of d is obtained.…”

Section: Resultsmentioning

confidence: 90%

Effects of partial substitution of Co by Ni on structural and transport properties of TiCoSb-based half-Heusler compound

Mahakal

Das

Singha

et al. 2022

J. Phys.: Conf. Ser.

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Correlation amid structural and transport properties of TiCo(1−x)Ni x Sb, (x=0.00, 0.02, 0.04, 0.06) alloy have been investigated. Samples have been synthesized by solid state reaction method, followed by arc-melting. Minute amount of CoTi embedded phase has been revealed by in-depth structural characterization using Rietveld refinement. Unit cell volume decreases with increasing Ni in TiCo(1−x)Ni x Sb, indicate sucessful substitution. Lattice strain, crystalline size and dislocation density have been estimated from x-ray diffraction data. Temperature dependent resistivity (ρ(T)) measurements have been carried out down to 10 K. Transition from metallic to semiconducting behavior is observed in ρ(T) data for x=0.00, 0.02. ρ(T) for x=0.04 and 0.06 show metallic nature. Plausible explanation have been provided on the basis of position of Fermi surface and embedded phases.

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“…This distinct behavior of κ for this last sample contrasts with the monotonic decrease in κ observed in earlier reports of TiCoSb. 10,54,55 This difference might be tied to the presence of Fe that leads to a shrinkage of the unit cell volume (a = 5.8897 Å for TiCoSb and a = 5.8854 Å for TiCo 0.85 Fe 0.15 Sb), thereby affecting the solubility limit of Sn in TiCoSb, or, alternatively, modifying the concentration of Fe in the HH matrix. In such a case, the actual chemical composition may differ from the nominal one, resulting in a departure from the observed monotonic trend in the transport properties with x up to x = 0.03.…”

Section: Structural Analysismentioning

confidence: 99%

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

Verma

Johari

Dubey

et al. 2022

ACS Appl. Mater. Interfaces

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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 TiCoSbhalf-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. A 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 nanosized grains evidenced by electron microscopy (field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM)), result 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 TiCo 0.85 Fe 0.15 Sb 0.97 Sn 0.03 . In addition, the microhardness and fracture toughness were found to be enhanced for all of 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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Compositional modulation is driven by aliovalent doping in n-type TiCoSb based half-Heuslers for tuning thermoelectric transport

Cited by 17 publications

References 40 publications

Low Lattice Thermal Conductivity in a Wider Temperature Range for Biphasic-Quaternary (Ti,V)CoSb Half-Heusler Alloys

Low Lattice Thermal Conductivity in a Wider Temperature Range for Biphasic-Quaternary (Ti,V)CoSb Half-Heusler Alloys

Effects of partial substitution of Co by Ni on structural and transport properties of TiCoSb-based half-Heusler compound

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

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