Band structure and thermoelectric properties of half-Heusler semiconductors from many-body perturbation theory

Zahedifar, Maedeh; Kratzer, Peter

doi:10.1103/physrevb.97.035204

Cited by 46 publications

(22 citation statements)

References 50 publications

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“…While these findings are in good agreement with existing theoretical results [48,85,86], experimental measurements exhibit n-type conductivity in these alloys. It is worthwhile to mention here that previous computational studies have also examined the effect of advanced approaches beyond the semilocal GGA functional such as the hybrid functional and the GW method for most of these alloys [31,52,[104][105][106]. The GW approximation based on the many-body perturbation theory provides qualitatively similar results as that of the GGA functional with the former being more reliable, elaborate but computationally very expensive.…”

Section: B Electronic Band Structure and Density Of Statesmentioning

confidence: 87%

“…The valence electrons in these alloys occupy all bonding electronic states, while antibonding states remain unoccupied thereby leading to the semiconducting band gap. Examples of thermoelectric materials belonging to this class of alloys include X NiSn and X CoSb (where X = Hf, Zr, Ti) [31][32][33][34][35][36][37] and NbCoSn-based alloys [38][39][40][41]. All the above mentioned half-Heusler alloys with a valence electron count of 18 are promising candidates for thermoelectric applications with large Seebeck coefficient of up to several hundred μV K −1 and moderate electrical conductivity.…”

Section: Introductionmentioning

confidence: 99%

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Decisive role of interstitial defects in half-Heusler semiconductors: An ab initio study

Dey

Dutta

2021

Phys. Rev. Materials

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Half-Heusler semiconductors satisfying 18-electron rule typically display promising characteristics for thermoelectric applications. A persistent inconsistency between the type of charge carriers in some of these alloys as obtained from experiment and theory however casts serious doubt on the computational prediction of new and efficient half-Heusler alloys. To gain insights into the origin of this disparity, we have investigated the effect of intrinsic point defects on the electronic structure of four frequently studied half-Heusler alloys of the form XY Z with Y being Ni or Co. Using state-of-the-art ab initio calculations, our study reveals that interstitial Ni and Co are energetically most stable point defects in these alloys. Remarkably, interstitial defect modifies the location of the Fermi level inside the band gap as well as the value of the band gap, thereby bringing in close agreement with the corresponding experimental result. This work thus highlights the decisive role played by interstitial defects in thermoelectric half-Heusler alloys, which may open a new avenue for deliberately utilizing these defects as a strategy for tailoring electronic structure and hence the corresponding thermoelectric properties.

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Section: B Electronic Band Structure and Density Of Statesmentioning

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Decisive role of interstitial defects in half-Heusler semiconductors: An ab initio study

Dey

Dutta

2021

Phys. Rev. Materials

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“…The relatively small changes are in-keeping with the established similarity between the bandstructures of the XNiSn parent materials. 64,65 By contrast, the calculations with interstitial Ni and Cu show the emergence of a new partially lled band at the conduction band minimum (X point; Fig. 7b and c).…”

Section: Dft Calculationsmentioning

confidence: 90%

Suppression of thermal conductivity without impeding electron mobility in n-type XNiSn half-Heusler thermoelectrics

et al. 2019

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“…We calculate an average of transport quantities in x, y and z crystalline directions, when using DFT derived bands in combination with BoltzTraP. Using the information of three crystallographic orientations, rather than the full anisotropy is known to give sufficient accuracy in thermoelectric calculations [50][51][52] . In the DFT calculations, spin orbit coupling (SOC) effects were not considered.…”

Section: B Ab Initio Electronic Structure Calculationsmentioning

confidence: 99%

Band alignment and scattering considerations for enhancing the thermoelectric power factor of complex materials: The case of Co-based half-Heusler alloys

Kumarasinghe

Neophytou

2019

Phys. Rev. B

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Producing high band and valley degeneracy through aligning of conducting electronic bands is an effective strategy to improve the thermoelectric performance of complex bandstructure materials. Half-Heuslers, an emerging thermoelectric material group, has complex bandstructures with multiple bands that can be aligned through band engineering approaches, giving us an opportunity to improve their power factor. Theoretical calculations to identify the outcome of band engineering usually employ detailed density functional theory for bandstructure calculations, but the transport calculations are kept simplistic using the constant relaxation time approximation due to the complications involved with detailed scattering physics. In this work, going beyond the constant relaxation time approximation, we perform an investigation of the benefits of band alignment in improving the thermoelectric power factor under different density of states dependent scattering scenarios. As a test case we consider the Co-based p-type half-Heuslers TiCoSb, NbCoSn and ZrCoSb. First, using simplified effective mass models combined with Boltzmann transport, we investigate the conditions of band alignment that are beneficial to the thermoelectric power factor under three different carrier scattering scenarios: i) the usual constant relaxation time approximation, ii) intra-band scattering restricted to the current valley with the scattering rates proportional to the density of states as dictated by Fermi's Golden Rule, and iii) both intra-and inter-band scattering across all available valleys, with the rates determined by the total density of states at the relevant energies. We demonstrate that the band-alignment outcome differs significantly depending on the scattering details. Next, using the density functional theory calculated bandstructures of the half-Heuslers we study their power factor behavior under strain induced band alignment. We show that strain can improve the power factor of half-Heuslers, but the outcome heavily depends on the curvatures of the bands involved, the specifics of the carrier scattering mechanisms and the initial band separation. Importantly, we also demonstrate that band alignment is not always beneficial to the power factor. In addition, we show that the bandstructure itself can undergo changes as the bands are aligned in practice, which further affect the band alignment optimization. Our work illustrates the importance of going beyond the constant relaxation time approximation, as well as understanding how the bandstructure of each material behaves when considering band alignment. arXiv:1905.07951v1 [cond-mat.mtrl-sci]

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Band structure and thermoelectric properties of half-Heusler semiconductors from many-body perturbation theory

Cited by 46 publications

References 50 publications

Decisive role of interstitial defects in half-Heusler semiconductors: An ab initio study

Decisive role of interstitial defects in half-Heusler semiconductors: An ab initio study

Suppression of thermal conductivity without impeding electron mobility in n-type XNiSn half-Heusler thermoelectrics

Band alignment and scattering considerations for enhancing the thermoelectric power factor of complex materials: The case of Co-based half-Heusler alloys

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