Boltzmann Transport Theory Research Articles

Effect of Ti Doping on the Structural, Electronic, Optical and Thermoelectric Properties of ZrO2: A Systematic DFT Approach

AbstractIn this work, the density functional theory (DFT) calculations in wien2k code to investigate the effect of (Titanium) Ti doping (25% and 50%) in ZrO2 is utilized. The negative values of the Ef, i.e., −2.14, −3.42 and −2.31 as well as energy versus volume curves show the stability of pure, 25% and 50% doped ZrO2. From band structure and density of states results it is confirmed that upon doping Ti, the band gap of ZrO2 become direct from indirect and reduces from 3.10 eV to 1.26(25% doped)/1.16(50% doped). The optical investigations reveal that incorporation of Ti improved the optical properties significantly, which show the significance of these materials for optoelectronic device applications. The thermoelectric properties are investigated using the Boltzmann transport theory. The Seebeck coefficient, electronic conductivity, thermal conductivity, power factor and figure of merit is calculated. The obtained results show that the under study compounds are best candidates for different thermoelectric applications.

Strain-induced thermal switches with a high switching ratio in monolayer boron sulfide

Manipulating the thermal conductivity of materials and achieving a high thermal switching ratio is very important in fields such as thermal management and energy conversion. In this study, by utilizing first-principles calculations and semi-classical Boltzmann transport theory, we find the lattice thermal conductivity (κl) of monolayer boron sulfide (BS) can reach values as low as 0.11 Wm−1 K−1 at room temperature, significantly lower than that of well-known two-dimensional materials with low thermal conductivity such as SnSe. This phenomenon is mainly caused by the strong lattice anharmonicity, which is primarily induced by the lone electron pairs. The effect of biaxial strain on κl is further investigated. It is found that a small strain of 2% can lead to a two orders of magnitude increase in κl. Moreover, this property remains stable within the strain range of 2%–7%, making it easier to achieve experimentally. The variation of κl with strain is mainly determined by the change in phonon lifetime, which is governed by the competition between the reduction of anti-bonding valence band states and the enhanced coupling between soft optical and acoustic phonons. Our results indicate that monolayer BS is a promising candidate material for thermal switches and energy conversion devices.

Potential thermoelectric material Tl3XS4 (X = V, Nb, Ta) with ultralow lattice thermal conductivity.

The demand for sustainable energy solutions has driven intensive research into advanced thermoelectric (TE) materials, to harness waste heat for efficient power generation. Recently, several studies have revealed that Tl3VS4 possesses an ultralow lattice thermal conductivity, despite its simple body-centered cubic lattice structure. This paper focuses on the TE properties of Tl3XS4 (X = V, Nb, Ta) compounds through a systematic exploration utilizing first-principles calculations and semiclassical Boltzmann transport theory. The results of the AIMD simulation and phonon calculation reveal the excellent dynamic stability and thermal stability of Tl3XS4 at 300, 500, and 700 K. Moreover, we find that the Tl3XS4 compounds present ultralow lattice thermal conductivity (<0.5 W m-1 K-1 at 300 K), and the nanostructure strategy is effective. Based on the outstanding Seebeck coefficient and ultralow lattice thermal conductivity, the optimal ZT values of Tl3VS4, Tl3NbS4, and Tl3TaS4 at 300 K are determined to be 1.17 (p-type), 0.84 (n-type), and 0.65 (p-type), respectively. Additionally, at each considered temperature, the maximum ZT values of p-type (n-type) Tl3XS4 follow the order: Tl3VS4 > Tl3NbS4 > Tl3TaS4 (Tl3NbS4 > Tl3VS4 > Tl3TaS4). Our results demonstrate that Tl3XS4 (X = V, Nb, Ta) compounds are promising thermoelectric materials. This exhaustive research enhanced our nuanced comprehension of the electronic, dynamic, and thermoelectric attributes of Tl3XS4 (X = V, Nb, Ta), thereby offering valuable insights into the TE field.

Unlocking the mechanical, thermodynamic and thermoelectric properties of NaSbS2: A DFT scheme.

The present study focuses on the ground state mechanical, acoustic, thermodynamic and electronic transport properties of NaSbS2 polymorphs using the density functional theory (DFT) and semi-classical Boltzmann transport theory. The mechanical stability of the polymorphs is affirmed by the calculated elastic tensor. The calculated elastic properties asserted that all the polymorphs exhibit soft, brittle, anisotropic nature containing dominant covalent bonding. The 2D polar graphs are used to describe the anisotropic characteristic of the elastic parameters. The estimated value of Young's modulus and lattice thermal conductivity suggested that the polymorphs could be suitable for thermal barrier coating. Heat capacity, melting temperature, thermal conductivities, Grüneisen parameter, and thermal expansion coefficient of the polymorphs have also been studied to demonstrate thermodynamic behavior. The predicted lower values of lattice thermal conductivity declared that NaSbS2 polymorphs exhibit excellent electrical conductivity and transport properties. The estimated Seebeck coefficient (S), power factor (PF) and figure of merit (ZT) suggested that n-type triclinic and monoclinic, as well as p-type trigonal NaSbS2, are better for thermoelectric applications. The optimal carrier concentration for monoclinic structure is 1021cm-3 for T<750K, while it becomes 1020cm-3 for T>750K. It is also found that the optimal carrier concentration of the trigonal is 1021cm-3, whereas it is 1020cm-3 for triclinic structures. Therefore, it can be stated that NaSbS2 polymorphs possess excellent thermoelectric features, making them a promising choice for thermoelectric (TE) applications.

Unveiling the impact of biaxial strain on phonon transport in Janus γ-Ge2SSe monolayer for thermoelectric applications

Thermoelectricity offers an efficient means of converting heat directly into electricity without greenhouse gas emissions. Recently, the hexagonal γ-GeSe phase and a new class of monolayers called Janus have been synthesized, exhibiting exceptional thermoelectric properties. In this study, we investigate the phonon thermal transport in γ-Ge2SSe Janus monolayers under biaxial strain using density functional theory and Boltzmann transport theory. Our analysis reveals that acoustic phonon modes, particularly the transverse acoustic and longitudinal acoustic modes, dominate the thermal transport. The lattice thermal conductivity (κl) shows a strong dependence on biaxial strain, with a decrease observed under tensile biaxial strain, and the Grüneisen parameter reveals considerable anharmonicity, which promotes phonon scattering and reduces thermal conductivity. At room temperature and at 0% strain, κl of Janus γ-Ge2SSe is measured at 4.41 W/mK, demonstrating moderate thermal transport, while under 2% tensile strain, κl decreases to 3.13 Wm−1 K−1, highlighting the material’s strain sensitivity. These results suggest that strain engineering can be effectively used to optimize the thermoelectric performance of Janus γ-Ge2SSe monolayers, providing valuable insights for energy conversion applications.

Spin relaxation in persistent spin textures

Abstract Spin relaxation due to the combined diffuse scattering and spin-orbit coupling (SOC) plays a crucial role for the efficient spin transport, which is a prerequisite for spintronic devices. Here, we investigate the spin relaxation in two-dimensional systems with different types of SOC, with a particular focus on the SOC with persistent spin texture (PSO). Based on the Boltzmann transport theory, we calculate spin diffusion matrices within the framework of Dyakonov-Perel mechanism. In the uniform case, it is found that the in-plane and out-of-plane spin relaxations for all considered SOCs are independent. Interestingly, the in-plane spin relaxation for certain PSOs reveals significant anisotropy characterized by the infinite spin relaxation time for the spin oriented along the direction of spin-orbit field. In the non-uniform case, we show that there always exists the static solution for the PSO with SU(2) symmetry, which corresponds the persistent spin helix in real space. Our work is expected to enrich the fundamental understanding of spin relaxation mechanism and provide new guidelines to design spin-orbitronic devices.

Comparative analysis of electronic, mechanical, vibrational, thermodynamical and thermoelectric properties of Li based quaternary Heusler’s LiNbRhAl, LiNbRhGa and LiNbRhIn alloys: A DFT study

We have performed a comprehensive demonstration of electrical, structural, dynamical, mechanical, thermodynamical and transport properties of Li based LiNbRhZ (Z= Al, Ga, and In) quaternary Heusler (QH) alloys utilising Density Functional Theory (DFT). Calculation of electronic properties via generalized gradient approximation (GGA) and Heyd-Scuseria-Ernzerhof (HSE06) hybrid method, disclose the semiconductor nature with indirect band gap. We found the bandgap calculated by HSE06 is close to experimental value as compared to GGA. Density of states (DOS) analysis shows that 4d states of Nb and Rh atoms contributed significantly to the valance and conduction band near Fermi energy. Absence of negative frequency in phonon dispersion curve shows the dynamical stability and the negative value of formation energy suggested the thermodynamic stability of these alloys. To confirm practical reliability, elastic and mechanical properties are calculated. The value of Pugh's ratio and Cauchy pressure ensures the ductile nature of studied alloys. We have calculated all thermoelectric (TE) parameters via Boltzmann Transport theory. The computed melting point of LiNbRhZ (Z = Al, Ga, and In) alloys are found to be 1911.69 ± 300 K, 1790.97 ± 300 K and 1788.42 ± 300 K respectively, which anticipate potential in high temperature thermoelectric devices. The role of lattice vibrations in total thermal conductivity is prominent only up to 300 K in all discussed alloys. The amazing thermoelectric characteristics of LiNbRhZ alloys render these quaternary Heusler alloys as possible thermoelectric materials in high temperatures.

Understanding phonon transport properties on Janus XSSe (X = Hf, Pb, Pt) monolayers via density functional theory

Janus monolayers have emerged as promising candidates for thermoelectric applications due to their unique structural and electronic properties. This study investigates the phonon thermal transport of Janus XSSe (X = Hf, Pb, Pt) monolayers using density functional theory (DFT) and Boltzmann Transport Theory (BTT). Our calculations reveal exceptionally low lattice thermal conductivities of 0.80, 1.43, and 11.0 W/mK for HfSSe, PbSSe, and PtSSe, respectively, at 300 K. The transverse acoustic (TA) phonon mode dominates the thermal transport, contributing 42.49%, 46.37%, and 46.82% to the total lattice thermal conductivity in these materials. Significant anharmonicity, characterized by low phonon lifetimes and reduced group velocities, further suppresses the lattice thermal conductivity. Additionally, we report indirect bandgaps of 1.49 eV, 0.64 eV, and 2.25 eV for HfSSe, PbSSe, and PtSSe, respectively. These findings highlight the potential of Janus XSSe monolayers for thermoelectric applications and provide insights into their phonon transport mechanisms.

First principles methodology for studying magnetotransport in narrow gap semiconductors with ZrTe5 example

The origin of resistivity peak and sign reversal of Hall resistivity in ZrTe5 has long been debated. Despite various theories proposed to explain these unique transport properties, there’s a lack of comprehensive first principles studies. In this work, we employ first principles calculations and Boltzmann transport theory to explore transport properties of narrow-gap semiconductors across varying temperatures and doping levels within the relaxation time approximation. We simulate the temperature-sensitive chemical potential and relaxation time in semiconductors through proper approximations, then extensively analyze ZrTe5’s transport behaviors with and without an applied magnetic field. Our results reproduce crucial experimental observations such as the zero-field resistivity anomaly, nonlinear Hall resistivity with sign reversal, and non-saturating magnetoresistance at high temperatures, without introducing topological phases and/or correlation interactions. Our approach provides a systematic understanding based on multi-carrier contributions and Fermi surface geometry, and could be extended to other narrow-gap semiconductors to explore novel transport properties.

Impact of strain and electron–phonon coupling on thermoelectric performance of Germanene

This manuscript describes the thermoelectric properties of monolayer germanene under the influence of biaxial strain using the combined approach of ab initio and semi-classical Boltzmann transport theory. To achieve excellent precision in the estimation of the thermoelectric behavior of strained germanene, the research delves into the temperature-dependent scattering time, particularly emphasizing the electron–phonon coupling effect. Incorporating both optical and acoustic phonons is always crucial and key for precisely estimating the scattering time, surpassing the limitations of the deformation potential approximation method. By examining the impact of strain on monolayer germanene and accounting for its scattering time, this approach provides a more practical means of gauging the thermoelectric performance of germanene under the presence of bi-axial strain. Moreover, the study extends its analysis to doped germanene with bi-axial strain, employing the rigid band approximation to investigate its thermoelectric performance. The research extensively estimates the transport properties for both intrinsic and extrinsic germanene, utilizing the hybrid functional HSE06. Additionally, the lattice thermal conductivity of germanene is estimated and compared for the strained and unstrained conditions. The analysis of thermal conductivity involves considering the effects of group velocity and phonon scattering time, providing insights into the nature of heat transport in strained germanene systems. Overall, this comprehensive study contributes to a deeper understanding of the thermoelectric properties of germanene under strain and lays the foundations for potential applications in electronic and thermal devices.

Investigation of optical and thermoelectric characteristics of novel zintl-phase alloys CaZn2X2 (X = P, As, Sb) for green energy applications

Abstract This study examines the photovoltaic and thermoelectric response of calcium-based novel Zintl-phase alloys CaZn2X2 (X = P, As, Sb). The structural, optoelectronics, and transport features of Zintl CaZn2X2 (X = P, As, Sb) compounds have been analyzed using the full potential linearized augmented plane wave (FPLAPW) technique. Investigations on formation energy and phonon dispersion have confirmed the formation and dynamical stabilities. These compounds exhibit a semiconductor behavior, as their predicted bandgap values: 1.76 eV for CaZn2P2, 1.14 eV for CaZn2As2, and 0.32 eV for CaZn2Sb2. By investigating the optical properties, we have discovered their potential applicability in optoelectronic and photovoltaic devices, as evidenced by the optical response of these phases. The traditional Boltzmann transport theory has assessed transport characteristics against temperature and chemical potential. Significantly higher values of the Seebeck coefficient are achieved at room and elevated temperatures. Moreover, the power factor demonstrates a linear relationship with rising temperature. The remarkable optoelectronic properties and exceptional power factor values suggest that these materials are suitable for deployment in photovoltaic and transport devices.

Low lattice thermal conductivity induced by antibonding sp-hybridization in Sb2Sn2Te6 monolayer with high thermoelectric performance: A First-principles calculation

Utilizing first-principles calculations and Boltzmann transport theory, the crystal structure, thermal and electronic transport, and thermoelectric (TE) properties of the Sb2Sn2Te6 monolayer are evaluated in the current work. The Sb2Sn2Te6 monolayer is an indirect band gap semiconductor with a band gap of 0.81 eV using the Heyd-Scuseria-Ernzerhof (HSE06) functional in combination with the spin-orbital coupling (SOC) effect. The antibonding states formed by the hybridization of Sb s orbital with Te p orbital near the Fermi level weaken the bonding strength of the Sb-Te bond, leading to significant anharmonicity and low group velocity. Thus, a low lattice thermal conductivity of 2.77 W/m K is achieved for the Sb2Sn2Te6 monolayer at 300 K. The band convergence and multivalley characteristics in the electronic band structure give birth to the enhancements of Seebeck coefficients and carrier mobilities, resulting in a substantial power factor of 76.69 μW/mK2 at 300 K under the carrier concentration of 3.20×1020 cm−3. An optimal figure of merit (ZT) of 2.37 at 900 K for the Sb2Sn2Te6 monolayer is obtained under the carrier concentration of 2.42×1020 cm−3. The present work not only provides fundamental insights into the correlation between the antibonding state, chemical bond and lattice thermal conductivity in Sb2Sn2Te6 monolayer, but also elaborates on the promising prospect of the Sb2Sn2Te6 monolayer in the TE application with high conversion efficiency.

Theoretical insights into Sb2Te3/Te van der Waals heterostructures for achieving very high figure of merit and conversion efficiency

Thermoelectric technology offers a promising solution for sustainable energy conversion, but maximizing efficiency and figure of merit (ZT) remains a significant challenge. This work explores the novel structural, electronic, and thermoelectric properties of Sb2Te3/Te van der Waals heterostructures (vdWHs) through first-principles computation and Boltzmann transport theory. Our study reveals that the Sb2Te3/Te vdWHs exhibit very low lattice thermal conductivity (0.28 Wm−1K−1) and high Seebeck coefficient (811 μVK−1), driven by energy-filtering effects across the interface and a band gap of 0.47 eV. Notably, the calculated ZT reaches a record-high value of 8.83 at 400 K, substantially surpassing previous benchmarks for similar materials. Unlike prior studies, we extend our investigation by tuning the dimensions to 2 × 2 × 1 and 3 × 3 × 1 supercells and exploring tri-layer Te/Sb2Te3/Te vdWHs. Our results show that the ZT of the 2 × 2 × 1 supercell reaches an even higher value of 9.14, further exceeding the performance of the unit cell. Additionally, the heterostructures demonstrate a remarkable thermoelectric conversion efficiency (η) of 32.25 % and thermionic refrigeration efficiency surpassing 51.9 % of Carnot efficiency at 400 K, highlighting their potential for high-performance cooling applications. These findings significantly advance the integration of high-efficiency heat-to-electricity conversion and cooling within a single material system, setting a new benchmark for thermoelectric performance and establishing Sb₂Te₃/Te vdWHs as a leading candidate for next-generation thermoelectric and electronic technologies.

Combined first-principles and Boltzmann transport theory methodology for studying magnetotransport in magnetic materials

Unusual magnetotransport behaviors, such as temperature-dependent negative magnetoresistance (MR) and bowtie-shaped MR, have puzzled us for a long time. Although several mechanisms have been proposed to explain these phenomena, the absence of comprehensive quantitative calculations has made these explanations less convincing. In our work, we introduce a methodology to study magnetotransport behaviors in magnetic materials. This approach integrates the anomalous Hall conductivity induced by the Berry curvature, with a multiband ordinary conductivity tensor, employing a combination of first-principles calculations and semiclassical Boltzmann transport theory. Our method also incorporates the temperature dependence of the relaxation time and the anomalous Hall conductivity, as well as the field dependence of the anomalous Hall conductivity. We initially test this approach on models, obtaining distinct behaviors of magnetoresistance and Hall resistivity across several types of magnetic materials, and then apply it to a Weyl semimetal Co3Sn2S2. The results, which align well with experimental observations in terms of magnetic field and temperature dependencies, demonstrate the efficacy of our approach. This methodology provides a comprehensive and efficient means to understand the underlying mechanisms of the unusual complex behaviors observed in magnetotransport measurements in magnetic materials. Published by the American Physical Society 2024

Comparative analysis of electronic and thermoelectric properties of strained and unstrained IrX3 (X = P, As) skutterudite materials

Abstract The electronic and thermoelectric properties of unfilled IrP3 and IrAs3 skutterudites materials under hydrostatic pressures are investigated using density functional theory (DFT) combined with semi-classical Boltzmann transport theory. Calculations of the elastic properties and phonon frequencies for both strained and unstrained materials demonstrate that they are mechanically and dynamically stable, with ductility varying based on the applied pressure. For pressures ranging from 0 to 30 GPa, the band structure calculations with the GGA+TB-mBJ approximation reveal that the band gap varies from 0.400 to 0.144 eV for IrP3 and from 0.341 to 0.515 eV for IrAs3. At 0 GPa, IrAs3 exhibits a direct band gap, whereas IrP3 has an indirect band gap. As pressure increases, IrAs3 undergoes a transition from a direct to an indirect band gap above 10 GPa, while IrP3 maintains its indirect band gap characteristic throughout the pressure range. &amp;#xD;The thermoelectric properties, at various pressures and temperatures between 300 and 1200 K, are also computed. These properties include the Seebeck coefficient, electrical conductivity, thermal conductivity (both electronic and lattice contributions), and relaxation time. The ideal conditions for efficient thermoelectric properties in IrAs3 are achieved at 30 GPa and 1200 K, with an optimal n-type doping concentration of 56×1019 cm-3, resulting in a ZT of 0.68. For IrP3, a ZT of approximately 0.46 is obtained at 600 K and 5 GPa, with a p-type doping concentration of 6.0×1018 cm-3.&amp;#xD;The present study provides valuable insights into the behavior of skutterudite materials under strain, offering pathways for enhancing their performance in practical applications.&amp;#xD;

Carbon monochalcogenides/graphene van der Waals heterostructures for sustainable energy harvesting

We constructed the van der Waals (vdW) heterostructures by stacking graphene (G) on top of carbon-based monochalcogenides (CX; X = S, Se, and Te) monolayer in two different patterns (I and II) and predicted various physical properties through first-principles calculations. Among the six heterostructures, three systems (CS/G in Pattern-I and II, and CSe/G in Pattern-II) were found to be most stable. Additionally, the calculated electronic properties confirmed that the CS/G and CSe/G heterostructures in Pattern II are indirect semiconductors with narrow band gap values of 0.49 and 0.30 eV, respectively. Notably, both heterostructures (CS/G and CSe/G) exhibit significantly larger electron carrier mobilities of 762.83 and 206.84 m2/Vs at room temperature, respectively. Furthermore, intrinsic and interface dipoles in both heterostructures were found to align along the +z axis, enhancing charge transfer at the interface and narrowing the band gap, particularly in CSe/G. This polarization effect contributes to the observed high electron mobility and thermoelectric performance. Electronic transport coefficients like the Seebeck coefficient, electrical conductivity, and thermoelectric power factor are predicted using the Boltzmann transport theory implemented in the BoltzTrap code. The highest power factor 249mW/mK2 was achieved for the CSe/G heterostructure at 300K, demonstrating its ability for good thermoelectric purposes. Besides, the computed optical properties revealed the potential of the CS/G heterostructure as a light absorber with an excellent solar light energy conversion efficiency (η) of 23.57 % for solar cell device applications. Our predictions show that the novel 2D CX/G vdW heterostructures could be promising candidates for designing new solar and heat energy harvesting devices.

First-principles study of the electron and phonon transport properties in monolayer boron monosulfide

Abstract Motivated by the excellent electronic properties of theoretical proposed monolayer boron monosulfides (BS) binary materials, which belong to a light-element member of the group IIIA chalcogenides family, we have investigated the electron and phonon transport properties of three monolayer phases of BS (α, β and γ) using first-principles and Boltzmann transport theory methods. The calculated electronic structures show that α- and β-BS are semiconductors with indirect bandgaps of 4.01 eV and 3.87 eV, respectively, whereas the γ-BS is a semiconductor with a direct bandgap of 2.97 eV. Additionally, due to their light carrier effective masses, superior high carrier mobilities are observed, thus bringing high Seebeck coefficients. We also find that due to the absence of imaginary phonon frequencies, the three monolayer phases of BS show dynamical stability. The phonon group velocity and relaxation time are also calculated to analyze the phonon thermal conductivity. We find that strong phonon scattering makes γ-BS monolayer possess extremely low phonon thermal conductivity (1.2 and 2.7 Wm−1K−1 along the x and y directions at 300 K, respectively), whereas α- and β-BS monolayers show a relatively high phonon thermal conductivity. Therefore, the highest predicted ZT value of 1.7 ( n -type) at 700 K is obtained for monolayer γ-BS along the x direction. However, α- and β-BS monolayers have extremely low ZT values. Our results reveal that the γ-BS monolayer has wider promising applications in high performance thermoelectric material than α- and β-BS monolayers.

Influence of biaxial and isotropic strain on the thermoelectric performance of PbSnTeSe high-entropy alloy: A density-functional theory study

Strain engineering is an effective method to improve materials thermoelectric (TE) performance. In this study, both biaxial and isotropic strains ranging from −3% to +3 % and from −3% to −1%, respectively, were applied to improve the TE properties of PbSnTeSe high entropy alloy (HEA). The effects of strain on the TE transport properties of PbSnTeSe HEA were investigated using first-principles calculations combined with Boltzmann transport theory. Under biaxial strain, n-type doped PbSnTeSe HEA shows an increase in the optimal power factor (PF) with both compressive and tensile strains. For p-type doping, compressive strain enhances the PF, whereas tensile strain reduces it. Within a strain range of −3% to +3 %, the optimal PF are 7.8–9.5 mW/mK2 for n-type and 0.85–1.3 mW/mK2 for p-type doped PbSnTeSe HEA. The maximum figure of merit (ZT) value of 1.63 for n-type doped PbSnTeSe HEA at 300 K under 3 % tensile strain is 61 % higher than the ZT value of 1.1 without strain. Under isotropic strain ranging from 0 % to −3%, the PF increases from 7.8 to 14 mW/mK2 for n-type and from 1.1 to 3.4 mW/mK2 for p-type doped PbSnTeSe HEA. Additionally, isotropic strain boosts the maximum ZT value for p-type doped PbSnTeSe HEA at 300 K from 0.3 to 0.85 under −3% strain. This study confirms that strain engineering is an effective strategy to enhance the thermoelectric properties of PbSnTeSe HEA.

First-principles insights into thermoelectric behavior of XNiAs (X = Sc, Y) half-Heusler compounds

Abstract Half-Heusler (HH) compounds are regarded as potential candidates for thermoelectric devices to convert waste heat energy into electrical power, which could help mitigate the ongoing energy crisis. In this study, we investigate the structural, electronic, magnetic, and thermoelectric properties of HH compounds XNiAs (X = Sc, Y) using Density Functional Theory (DFT) and semi-classical Boltzmann transport theory (BTE). The compounds are non-magnetic semiconductors with an indirect band gap of 0.48 ( 0.50) eV for ScNiAs (YNiAs) respectively. Both materials show dynamic and mechanical stability, with ScNiAs displaying brittleness and YNiAs exhibiting ductility. At room temperature, the lattice thermal conductivity (κ l ) for ScNiAs is 28.67 W/mK, while for YNiAs, it is 15.21 W/mK and both decrease as the temperature rises. The highest value of power factors is 29.03 μW/cmK2 and 29.74 μW/cmK2 for ScNiAs and YNiAs respectively at 1100 K for n-type doping. The optimal values of the figure of merit (zT) for n-type doping are 0.33 for ScNiAs and 0.58 for YNiAs at 1100 K. Both compounds exhibit better thermoelectric performance for n-type doping compared to p-type doping. The presence of flat bands and higher κ l limits these materials from achieving higher zT values.

Validation of galvanomagnetic and thermomagnetic transport measurements using Standard Reference Material 3451.

In the "method of four coefficients," electrical resistivity (ρ), Seebeck coefficient (S), Hall coefficient (RH), and Nernst coefficient (Q) of a material are measured and typically fit or modeled with theoretical expressions based on Boltzmann transport theory to glean experimental insights into features of electronic structure and/or charge carrier scattering mechanisms in materials. Although well-defined and readily available reference materials exist for validating measurements of ρ and S, none currently exists for RH or Q. We show that measurements of all four transport coefficients-ρ, S, RH, and Q-can be validated using a single reference sample, namely, the low-temperature Seebeck coefficient Standard Reference Material® (SRM) 3451 (composition Bi2Te3+x) available from the National Institute for Standards and Technology (NIST) without the need for inter-laboratory sample exchange. RH and Q data for NIST SRM 3451 reported here for the temperature range 80-400K complement the data already available for ρ and S and will therefore be of interest to researchers desiring to validate new or existing galvanomagnetic and thermomagnetic transport properties measurement systems.