half-Heusler Alloys Research Articles

Tuning conduction properties and clarifying thermoelectric performance of P-type half-Heusler alloys TiNi1−xCoxSn (0 ≤ x ≤ 0.15)

TiNiSn is an N-type thermoelectric material with a high-power factor composed of low toxicity and abundant elements. TiNiSn also shows P-type electrical conduction by hole doping. In this study, we tune the conduction properties of TiNi1−xCoxSn (0 ≤ x ≤ 0.15) with Co substitution at the Ni site. The samples were prepared by the arc melting method, and thermoelectric properties were investigated up to 800 K. The results of the Hall effect and the Seebeck coefficient measurements indicate that the majority of charge carriers changes from electrons to holes at x ≥ 0.03, suggesting that Co acts as an acceptor. We report for the first time that Ti0.994Ni1.00Co0.051Sn1.01 exhibits ZT = 0.12 at 675 K. This work reveals that Ti0.994Ni1.00Co0.051Sn1.01 could be a potential P-type thermoelectric material operating at high temperatures.

Topological signatures of triply degenerate fermions in Heusler alloys: an ab initio study

Triply degenerate nodal point (TP) fermions, lacking elementary particle counterparts, have been theoretically anticipated as quasiparticle excitations near specific band crossing points constrained by distinct space-group symmetries instead of Lorentz invariance. Here, based onfirst-principlescalculations and symmetry analysis, we demonstrate the presence of TP fermions in Heusler alloys. Furthermore, we predict that these Heusler alloys are dynamically stable, exhibiting TP fermions along four distinctC3axes in the F-43m space group. We show thatα-LiCaPdSb harbours peculiar Fermi arcs and surface states on the (111) and (001) crystal facets, owing to the coexistence of threefold rotational and time reversal symmetry. More interestingly, a modest tensile strain can increase the distance of fermions along the Γ-Lhigh symmetric line by as much as 21.10%, which give rise to measurable Fermi arcs. Furthermore, we investigate non-trivial topological insulator phase inβ-LiCaPdSb, by changing the chemical environment through placing transition metal atoms at various Wyckoff positions. Theβ-LiCaPdSb harbour a semi-metallic nature, and by breaking cubic symmetry, it undergoes a transition from semi-metal to a non-trivial topological insulator. In addition, for the first time, rare-earth LaPtBi half-Heusler alloy is examined under strain to uncover multiple band inversions associated with the TP fermionic phase. The observed multiple band inversion is entirely unaffected by spin-orbit coupling. We show that the LaPtBi compound hosts TP fermions, which are linked to aZ2topological invariant. Remarkably, with clear band crossings and multiple band inversion, we point out the possibilities of the LaPtBi for displaying a rich topological phase diagram. Our work provides a prototype material platform for experimental detection through angle-resolved photoemission spectroscopy or scanning tunnelling spectroscopy and practical spintronic applications.

Unveiling half-metallic, thermoelectric and optoelectronic behavior of the new Heusler alloy RbCrZ (Z = Si, Ge): a DFT perspective

Abstract Utilizing the density functional theory (DFT) method, this study aims to predict with precision the structural, elastic, electronic, magnetic, thermoelectric, thermal, and optical properties of two recently discovered half-Heusler alloys, namely RbCrSi and RbCrGe. The exchange and correlation potential are accounted for using the generalized gradient approximation of Perdew–Burke–Ernzerhof (GGA-PBE) and the Tran–Blaha-modified Becke–Johnson exchange potential (TB-mBJ). Through structural analysis, it is observed that both RbCrSi and RbCrGe alloys exhibit energetic stability in a type-3 structure with a ferromagnetic (FM) state. Both alloys exhibit half-metallic properties and integer magnetic moments of 3 μB, following the Slater-Pauli rule. Additionally, elastic calculations confirm their mechanical stability and anisotropic ductile behavior. The quasi-harmonic Debye model (QHDM) is employed for calculating thermodynamic properties, while the BoltzTraP code, based on semi-classical Boltzmann theory (SCBT), is utilized for evaluating thermoelectric properties. Findings reveal that RbCrZ alloys (with Z = Si, Ge) exhibit high figure of merit (ZT) values nearing unity at highest temperature. Consequently, the newfound half-Heusler alloys RbCrSi and RbCrGe hold significant promise for applications in thermoelectricity and spintronic devices. This comprehensive analysis underscores the potential of these alloys in the realm of renewable energy applications.

Theoretical Insights into Off-Stoichiometric Zr(x)Ti(1-x)IrSb Half-Heusler Alloys: A First Principle Calculations.

This study presents a theoretical investigation into the phase stability, electronic, and optical properties of off-stoichiometric Zr_{x}Ti_{1-x}IrSb (x = 0, 0.0625, 0.1875, 0.25, 0.50, 0.75, 1) compounds. Using first-principles calculations, we explore how varying Zr and Ti concentrations can tune the electronic and optical properties of these half-Heusler alloys. The Structural, optical, and electronic properties were meticulously analyzed with both the GGA-PBE and Meta-GGA-SCAN approximations, as implemented in the Vienna Ab initio Simulation Package (VASP). The dynamical stability of these compounds was assessed using the Phonopy package. Our findings reveal that these alloys exhibit semiconductor behavior with tunable band gaps, and their optical properties show significant variation across different compositions, particularly in the visible light range. The compounds also demonstrate robust dynamical stability, indicating their potential for practical applications in electronic and optoelectronic devices. These results underscore the versatility of Zr_{x}Ti_{1-x}IrSb alloys and highlight their promise for next-generation technology.

First-principles investigation of electronic, magnetic, and optical properties of FeMnSb/GaZ (Z = As or P) interfaces

We systematically investigated the electronic, magnetic, and optical properties of the FeMnSb half-Heusler alloy, its (001) surface, and its interfaces with GaAs and GaP semiconductors by using first-principles calculations based on density functional theory. The bulk FeMnSb reveals its half-metallic ferrimagnetism with 100% spin-polarization. Extending this study to the (001) surface, we uncover distinct electronic and magnetic behaviors for Fe- and MnSb-terminated surfaces, the MnSb-terminated surface preserving the half-metallicity observed in the bulk material. Our evaluation of the interfaces exhibits positive work of separation, indicating that these interfaces are energetically favorable. The density of states analysis reveals that all interfaces exhibit a metallic nature. High spin-polarization values, particularly 97.316% for the Fe-Ga interface, suggest a substantial degree of spin-polarized current. Notably, the absorption coefficient peaks shift from the ultraviolet (UV) region in the bulk alloy to the visible region at the (001) surfaces. However, at the FeMnSb/GaAs and FeMnSb/GaP interfaces, the highest absorption peaks revert to the UV region, highlighting strong interfacial coupling effects. These results suggest the tunability of FeMnSb optical properties via surface termination and interface engineering, making it a promising candidate for spintronic and optoelectronic applications.

Ferrimagnetic half metals TaMnZ (Z = As, Sb, Bi) for thermoelectric and spintronic applications – Material computations

Half metals possess coupling behavior of metals and semiconductors with wide heat transport and spin transport properties. This research article covers the structural, mechanical, electronic, magnetic and thermoelectric properties of the half Heusler alloys TaMnZ (Z = As, Sb, Bi). The equilibrium lattice constants and corresponding ground state energies show that the studied alloys are stable in the ferrimagnetic cubic phase. The band dispersion plots suggest that the compounds TaMnAs, TaMnSb and TaMnBi are half metals with indirect band gap having the band gap energies of 1.13 eV, 1.24 eV and 1.12 eV respectively in the spin down channel. As the materials have 100 % spin polarization with an integer magnetic moment of −1 μB, they are suitable for making spintronic devices such as spin transistors and spin-flip flops. The temperature-dependent thermoelectric properties of the alloys have been studied by classical Boltzmann theory. The materials have low lattice thermal conductivity which was confirmed by Slack’s equation. The obtained thermoelectric figure of merit for p-type TaMnAs, TaMnSb and TaMnBi is 0.7, 0.6 and 0.8 respectively at 1200 K. Similarly, the figure of merit obtained for n-type TaMnAs, TaMnSb and TaMnBi is 0.6, 0.64 and 0.8 respectively at the same temperature. The favourable heat and spin transport properties of these alloys show that they are the potential characters to figure out better thermoelectric and spintronic performance.

DFT study of structural, electronic, magnetic, elastic, and thermoelectric properties of Ta-based half-Heusler alloys CsTaX (X = C, Si, and Ge) for spintronics and thermoelectric technologies

The structural, electronic, elastic, magnetic, and thermoelectric characteristics of three novel Ta-based half-Heusler alloys, CsTaC, CsTaSi, and CsTaGe, have been investigated using the Full-Potential Linearized Augmented Plane Wave (FP-LAPW) method within the density functional theory (DFT). The volume-optimization graphs show that all compounds are stable in the ferromagnetic (FM) phase. Half-Metallicity of these compounds is confirmed by the density of states (DOS) and band structures. The total magnetic moment for CsTaC is 6 μB, and for CsTaX (X = Si, Ge) is 2 μB. The negative pd exchange energy and exchange constants confirm ferromagnetism. The values of Pugh’s ratio (B/G) and Poisson’s ratio (v) reveal that CsTaC is ductile and CsTaX (Si, Ge) is brittle. The thermoelectric response is estimated using the BoltzTraP code, demonstrating that at room temperature, maximum ZT values for CaTaC, CsTaSi, and CsTaGe are 0.99, 0.97, and 0.90, respectively. Consequently, CsTaX (X = C, Si, and Ge) are suitable candidates for spintronic and thermoelectric technologies.

Optoelectronic and Thermoelectric Properties of Zirconium Half-Heusler Alloys RhZrX (X = P, As, Sb, Bi): an ab-initio Investigation

Optoelectronic and Thermoelectric Properties of Zirconium Half-Heusler Alloys RhZrX (X = P, As, Sb, Bi): an ab-initio Investigation

Alkali-based half metals as sustainable materials for spin electronics and energy harvesting application — Materials computation

The structural, mechanical, electronic, magnetic, and thermoelectric properties of alkali-based half-Heusler alloys (LiCrGe, LiCrSn, and LiCrPb) are investigated using the Wien2k code. These alloys exhibit half-metallic behavior in both ferromagnetic and antiferromagnetic phases. A phase transition from a stable ferromagnetic phase to a more stable antiferromagnetic phase indicates ductility. In the antiferromagnetic phase, using GGA exchange–correlation functional with 10,000 K-points, a band gap is observed in the spin-up state, with band gap energies of 0.9367 eV, 0.7762 eV, and 0.7913 eV, respectively. The alloys have a spin magnetic moment of −3μB, consistent with the Slater–Pauling rule. They also exhibit high Curie temperatures and 100% spin polarization in the spin-down state. The alloys LiCrZ (Z = Ge, Sn, Pb) shows promising thermoelectric behavior. Using the BolzTrap package, we observed, high Seebeck coefficient, electrical conductivity, low thermal conductivity, and enhanced power factor. The p-type LiCrZ (Z = Ge, Sn, Pb) compounds show thermoelectric figure of merit of 0.52, 0.76, and 0.84 at 1200 K, while n-type compounds have figure of merit of 0.56, 0.65, and 0.80 at the same temperature. These properties make these materials promising for spintronic and thermoelectric applications.

Ab-initio investigation of the structural, mechanical, electronic, thermodynamic and optical properties of V2FeNiGe2 and Hf2FeNiSb2 double half-Heusler compounds

In the present work, using ab-initio density-functional theory methods based on the Quantum ESPRESSO package, we have investigated the structural, elastic, electronic and optical properties of 18–electron V2FeNiGe2 and Hf2FeNiSb2 double half-Heusler alloys. The calculated elastic properties suggest a ductile behavior with metallic bonding for V2FeNiGe2 and a brittle behavior with covalent bonding for Hf2FeNiSb2. The thermodynamic properties (Debye temperature, melting temperature) are also predicted and discussed for the studied alloys. The alloys are found to be semiconducting with indirect band gaps of 0.53eV for V2FeNiGe2 and 0.47eV for Hf2FeNiSb2. We also computed and analyzed their optical properties (dielectric function, optical conductivity, refractive index, absorption index and reflectance) and our calculations suggest that both materials have high absorption coefficient and optical conductivity in the UV as well as visible region. The results make them potential candidates for the manufacture of opto-electronic devices.

Study of the physical properties of the half-heusler XBrH with (X= sr, Ca and mg) compounds

Half-Heusler alloys are among the most promising thermoelectric materials for medium- and high-temperature waste heat recovery applications. This study investigates the physical properties of Half-Heusler compounds XBrH, with X = Sr, Ca, and Mg. We explored the structural, electronic, optical, and thermoelectric properties of these compounds using density functional theory (DFT) as implemented in the Wien2k package. The Generalized Gradient Approximation (GGA) as proposed by Perdew-Burke-Ernzerhof (PBE) and the modified Becke-Johnson (mBJ) functional were employed to calculate the exchange-correlation interactions. After doing structural optimization for a range of parameters, we discovered that the SrBrH compound is more stable than the CaBrH and MgBrH compounds. Our results show that the density of state calculations indicate semiconductor behavior for the XBrH with (X = Sr, Ca, and Mg) compounds. We also evaluated the real and imaginary parts of the dielectric tensor, the refractive index, the absorption coefficient, the electron energy loss, and the real and imaginary components of the optical conductivity, among other optical parameters. Additionally, we investigated the figure of merit (ZT), electronic and lattice thermal conductivity, Seebeck coefficient, and electrical conductivity. The MgBrH, CaBrH and SrBrH compounds showed p-type behavior, with positive values for the Seebeck coefficient and the greatest value of ≈180 μV/K, according to the thermoelectric data. At 1000 K, the ZT reach their highest values for CaBrH, SrBrH, and MgBrH, respectively, at 2.9, 2.8, and 0.9. The physical properties of the XBrH with (X = Sr, Ca, and Mg) compounds have been studied in detail.

High-entropy-driven half-Heusler alloys boost thermoelectric performance

High-entropy-driven half-Heusler alloys boost thermoelectric performance

First-principles calculations to investigate optoelectronic of transition-metal half-Heusler alloys MTiSn (M = Pd and Pt) for optoelectronics applications

The structural, mechanical, optical, and electronic properties of half-Heuslers MTiSn (M = Pd and Pt) are investigated using FP-LAPW incorporating the GGA-PBE. MTiSn crystallize in ferromagnetic (FM) and cubic structure (F-43m; C1b) with lattice constants of 6.216 Å and 6.241 Å, respectively, in good agreement with the available data. Elastic constants Cij reveal that MTiSn meet the mechanical stability criteria with notable thermodynamic properties. Also, we have conducted a detailed analysis of optical properties, encompassing the dielectric function, absorption coefficient, optical conductivity, optical refractivity, and extinction coefficient. It is found that PtTiSn shows higher optical responses than PdTiSn at low and high energy ranges. In terms of electronic properties, MTiSn demonstrate narrow bandgap semiconductor characteristics with an indirect bandgap of Eg = 0.507 eV (M = Pd) and Eg = 0.782 eV (M = Pt). The notable optoelectronic responses have also been examined, indicating the high potential of MTiSn materials for optoelectronic applications.

Ab initio analysis of structural, electronic, magnetic, thermodynamic, and elastic properties of Half Heusler alloys ZMnAs (Z = Be, Mg) for spintronics applications

In this study, the structural, electronic, magnetic, thermodynamic, and elastic attributes of ZMnAs (Z = Be, Mg) have been investigated. These Half-Heusler alloys exhibit stability in the ferromagnetic state (FM), as demonstrated by optimization-related energy release. The half-metallicity (HM) of these compounds is examined through the band structures and density of states (DOS). In addition, the crystal field and exchange energies are reported to confirm the control of electron spin. Additionally, the double exchange process and exchange constants were premeditated. In this case, ferromagnetism (FM) is caused by the quantum exchange of electrons, as evidenced by the negative pd exchange energy and the exchange constants, rather than being a result of clustering effects. The quasi-harmonic Debye model, included within the Gibbs code, was utilized to calculate the thermodynamic properties. These two compounds are mechanically stable and show ductile nature confirmed by the value of Poisson's ratio (v), Pugh's ratio (B/G), and Cauchy pressure (CP), which demonstrates the ability to withstand substantial plastic deformation before fracturing. Based on our calculations, the half-metallic (HM) nature, thermodynamic, ferromagnetic, ductile, and high inherent magnetic moment have been evaluated. These alloys are crucial in the advancement of spintronics and renewable energy systems.

First Principles Study of Structural, Electronic, Mechanical and Density of State Properties of the Half - heusler Alloy NaCrGe

In this study, the investigated structural parameters revealed that NaCrGe is stable at beta phase. We obtained that the material is a narrow bandgap semiconductor half-Heusler alloys with measured gap of 1.050 eV. The structure NaCrGe conduction band minimum (CBM) position at gamma(Γ) and the valence band maximum (VBM) located at X-point of the Brillouin zone. This indicates that the alloy NaCrGe has indirect bandgap semiconductors. The material NaCrGe is considered hybrids between metals and semiconductors. Hence, NaCrGe is Half-metallic heusler alloy. The calculated mechanical properties indicate that NaCrGe possesses good mechanical stability, making it suitable for structural applications. B/G ratio for NaCrGe is 2.40. This implies that NaCrGe is “ductile” in nature at ambient condition. Also NaCrGe is confirmed “ductile” in nature at positive value of C11 – C44 (+48.07). PDOS shows that Na-4p, Cr-4p and Ge- 2p has the highest orbital contribution for Na, Cr and Ge atoms respectively. At fermi energy both spin up and spin down is at zero point in the plot of projected density of state (PDOS) against energy. This revealed that NaCrGe is a half metallic heusler alloy.

Enhanced thermoelectric performance of Zr1−xNiSnTax half-Heusler alloys: a first-principle study

Enhanced thermoelectric performance of Zr1−xNiSnTax half-Heusler alloys: a first-principle study

Effect of single and dual doping on the thermoelectric properties of FeVSb0.95Sn0.05 and Fe0.95Co0.05VSb0.90Sn0.10 half-Heusler alloys

FeVSb in addition to a set of novel FeVSb0.95Sn0.05 and Fe0.95Co0.05VSb0.90Sn0.10 half-Heusler alloys were fabricated by arc melting followed by induction melting simple methods. Impacts of single Sn-doping and double Co- and Sn-doping on the structural and thermoelectric properties of FeVSb were investigated in this article. Structural and thermoelectric properties of FeVSb, FeVSb0.95Sn0.05 and Fe0.95Co0.05VSb0.90Sn0.10 compounds have been extensively studied in this work. N-type conduction was confirmed for the FeVSb system and for the doped FeVSb0.95Sn0.05 and Fe0.95Co0.05VSb0.90Sn0.10 alloys. The absolute value of Seebeck coefficient for the single Sn-doped sample increased from 127 μV/K to 155 μV/K, with the temperature increasing. Similarly, the Seebeck coefficient of the double Co- and Sn-doped alloy also increased from 40 μV/K to 60 μV/K. The thermoelectric power factor was notably enhanced for the dual doped Fe0.95Co0.05VSb0.90Sn0.10 alloy reaching 14 μW/cm.K2. Lattice thermal conductivity of the single Sn-doped FeVSb0.95Sn0.05 alloy decreased considerably over the whole temperature range. A maximum zT of 0.084 was achieved for FeVSb0.95Sn0.05 alloy at 575 K. The improved figure of merit due to doping is attributed to the phonon scattering at point defects. Sn-doping has significantly reduced thermal conductivity due to the enhanced point-defect and electron–phonon scatterings which contributed to improved thermoelectric figure of merit. Our findings showed also that the room-temperature thermal conductivity is seriously reduced via Sn and Co dual doping leading to higher ZT value for Fe0.95Co0.05VSb0.90Sn0.10 alloy. Promising candidates for further thermoelectric applications could be achieved by Sn-doping and double Co- and Sn-doping.

Strain induced ductile to brittle transitions of NiNbAl half-Heusler alloy

The present work is to explore the effect of strain on NiNbAl, half-Heusler alloy. We have investigated the properties of NiNbAl half-Heusler alloy using Density Functional Theory (DFT). The isotropic strains (tensile and compressive) are applied to examine the occurrence of phase transitions in the alloy. Induction of strain alters the electronic, mechanical and thermodynamic properties of the alloy. On application of strain, the alloy undergoes transition from semimetal to direct band gap semiconductor at 4 % tensile strain and semimetal to metallic transition at −6% compressive strains. This electronic phase transitions occur due to the change in the interatomic distance between the atoms in the alloy. It is found that the energy band gap value increases up to 12 % tensile strain and starts decreasing for the further increase in tensile strain. The mechanical properties of the alloy under strains are analysed and their variation under compressive and tensile strains are compared. The alloy undergoes ductile to brittle transitions on increasing the strain beyond 4 %. The phonon dispersion curves for different strains indicate that the alloy is thermodynamically stable under strain. The present results emphasis the effect of strain on electrons, phonons and the mechanical stability of the alloy which will pave way for designing flexible semiconducting devices with suitable device functionalities.

Electronic and thermoelectric behaviour of XCaB (X = Li, Na, K) half-Heusler alloys under strain

Impact of isotropic strain (≤±10 %) on electronic and thermoelectric properties of XCaB (X = Li, Na, K) half-Heusler alloys is studied using DFT method. LiCaB possesses the maximum structural, dynamical and mechanical stability among the considered alloys. The alloys remain ferromagnetic and most of them also retain half-metallicity even in strained conditions. Inclusion of lattice thermal conductivity (κl) lowers the total figure of merit (ZTtot) to almost half (∼0.6 at 800K) of that of electronic figure of merit (ZTel) (∼1 at 200K). Ductility detests κl but favours ZTtot. Application of strain could tune electronic band structure and/or mechanical behaviour of LiCaB, KCaB increasing ZTtot to about 0.75, 0.67, respectively, at relatively larger compressive strains, except for a negligible change in NaCaB. Thus, required modifications in electronic and mechanical properties of XCaB alloys are beneficial for thermoelectric performance and can be achieved under appropriate strain application.

Structural, electronic, magnetic, and thermoelectric properties of half Heusler alloys ZrCo1-XFeXSb (X = 0, 0.25, 0.5, 0.75, 1): A DFT study

The structural, electronic, magnetic, and thermoelectric properties of half-Heusler alloys ZrCo1-XFeXSb (X = 0, 0.25, 0.5, 0.75, 1) are investigated using the density functional theory. It is evident that ZrCoSbis a non-magnetic semiconductor. This study investigates the influence of substituting Fe for Co on the electronic structure and magnetic characteristics of ZrCoSb. The alloys transform into half-metallic ferromagnets as Fe substitutes Co. The indirect band gap of the ZrCo1-XFeXSb alloys decreases with increasing Fe content. The phonon dispersion curve is studied to determine the structural stability. The calculated values for the elastic constant for each composition satisfy the criteria for mechanical stability. To analyse its thermoelectric properties, the semi-classical Boltzmann transport theory is used to determine the Seebeck coefficients, electrical and thermal conductivities, and power factor as a function of temperature.