half-Heusler Alloys Research Articles

DFT studies on electronic, magnetic and thermoelectric properties of half Heusler alloys XCaB (X = Li, Na, K and Rb)

In this work, the results of first principles calculations of structural, electronics, magnetic and thermoelectric properties of half Heusler alloys XCaB (X = Li, Na, K and Rb) are presented. The pseudopotential method as implemented in the Quantum Espresso package has been used with the exchange correlation functional of Perdew, Burke and Ernzerhof (PBE). The total energy calculations show that the proposed alloys are in stable ferromagnetic phase and the calculated equilibrium lattice constant are in good agreement with the earlier reported results. All the alloys show strong spin polarisation of energy states near the Fermi level confirming ferromagnetic nature and also semiconducting for majority spin channel and metallic for down spin channel exhibiting half metallic property. The calculated magnetic moment of all the alloys XCaB (X = Li, Na, K and Rb) is around 2.00 µB mainly arises from the np electrons of B atom with partial involvement of nd electrons of Ca atom. The thermoelectric properties of the materials are calculated using the BoltzTrap code. The calculated transport properties like electrical conductivity, thermal conductivity and power factor increases with temperature which is a perfect fit for thermoelectric applications. The half metallic gap, strong spin polarization and high figure of merit (ZT) values shows that these studied materials can be used for both spintronics and thermoelectric device applications.

Theoretical Insight into the Stability, Magneto-electronic and Thermoelectric Properties of XCrSb (X: Fe, Ni) Half-Heusler Alloys and Their Superlattices

Theoretical Insight into the Stability, Magneto-electronic and Thermoelectric Properties of XCrSb (X: Fe, Ni) Half-Heusler Alloys and Their Superlattices

Structural, electronic and magnetic properties of the Half-Heusler alloy CrZSi (Z = Sc, Ti)

The structural, electronic and magnetic properties of the half-Heusler alloys CrZSi (Z = Sc, Ti) were studied using Density Functional Theory (DFT) based on pseudopotential method to explore the Cr-based ferromagnetic half-metallic alloys. The effect of substitution of scandium and titanium in Slater-Pauling behaviour, half-metallicity and mechanical properties were studied to understand the role of low valent transition element in half-Heusler compound. CrTiSi shows half-metallicity with an indirect bandgap of the value 0.765 eV. The robustness of half-metallic behaviour at different hydrostatic pressures were calculated. CrTiSi obeys Slater-Pauling rule and has integer magnetic moment of 4 μB. The mechanical properties were studied for both CrScSi and CrTiSi compounds to obtain elastic constants and moduli. The present work reveals the ductile nature of the compounds as their B/G ratio is >1.75 with positive Cauchy pressure. Further, phonon calculation with absence of negative frequencies determines the dynamical stability of the compound.

The Role of Magnetic Interaction on the Thermoelectric Performance of ZrNiSn Half‐Heusler Alloys

The half‐Heusler (HH)‐based materials are appealing for mid‐high temperature thermoelectric (TE) applications. Herein, the effect of Mn doping on the TE properties of ZrNiSn HH alloy is explored. The samples of ZrNi1−xMnxSn (x = 0.01–0.03) are prepared via the fast‐processing route comprising arc melting along with spark plasma sintering and then characterized for structural as well as TE properties. The Seebeck coefficient at room temperature with Mn doping is realized to be increased as a result of increased carrier effective mass, which might be due to the charge carrier–magnetic moment interaction. The improved power factor of ≈3.8 × 10−3 Wm−1 K−2 at ≈873 K is noticed for the composition ZrNi0.97Mn0.03Sn. The figure of merit is observed to be more or less unaltered with Mn concentration due to the simultaneously increased thermal conductivity.

Electronic, Structural, Mechanical, and Thermodynamic Properties of CoYSb (Y = Cr, Mo, W) Half-Heusler Compounds as Potential Spintronic Materials

We used density functional theory (DFT) calculations to investigate the structural, electronic, magnetic, mechanical, and thermodynamic properties of CoYSb (Y = Cr, Mo and W) compounds. These are XYZ type half-Heusler alloys, which also exist in the face centred cubic MgAgAs-type structure and conform to F4¯3m space group. We computed these properties in three different atomic arrangements known as Type-I, Type-II, and Type-III phases. In all these phases, the alloys were found to be in the ferromagnetic state. Furthermore, the calculated electronic band structure and the total electronic density of states indicated a metallic behavior in CoWSb, nearly half-metallic behavior in CoMoSb, and half-metallic behavior in CoCrSb, with a minority-spin band gap of 0.81 eV. Furthermore, the calculated mechanical properties predicted an anisotropic behavior of these alloys in their stable phase. Finally, due to its high Debye temperature value, CoCrSb shows stronger covalent bonding than CoMoSb and CoWSb, respectively.

Mechanical and heat transport properties of Ti[formula omitted]Zr[formula omitted]NiSn half-Heuslers: A molecular dynamic simulation study using ab initio-based interaction potentials

We have developed an interatomic potential tailored to represent in the range of temperatures between 100 K and 1300 K interactions among the different species composing Ti1−xZrxNiSn half-Heusler alloys over the whole range of x. To obtain the potential we considered an embedded atomic model (EAM). The EAM potential was parametrized throughout the fitting to structural formation energies, forces, and stresses produced by ab−initio calculations in selected Ti1−xZrxNiSn structures. With the help of the potential, we study two fundamental aspects of Ti1−xZrxNiSn half-Heuslers by molecular dynamics. The first is related to the heat carried by the lattice vibrations. The second aspect considers the mechanical strength as measured by the Young’s modulus. The simulations agree well with the experimental results for regular ternary half-Heuslers and alloy compositions. For instance, we found that lattice heat conductivity is always larger in ZrNiSn than in TiNiSn, and that ZrNiSn shows the highest Young’s modulus. From the results we can derive strategies for developing new nanostructured materials with improved properties for thermoelectric applications. Quite remarkably, the lattice thermal conductivity is reduced by almost a half in Ti1−xZrxNiSn layered structures. The methodology that we describe here is of great importance since it offers the possibility to improve the design of materials for thermal management devices.

Nanoscale-Thick Ni-Based Half-Heusler Alloys with Structural Ordering-Dependent Ultralow Magnetic Damping: Implications for Spintronic Applications

Atomic ordering and its consequence on the crystal structure are fundamental issues in the application of half-metallic Heusler alloys considered as a high spin-polarized electron source. NiMnSb is a promising half-metallic half-Heusler alloy for spintronic devices due to its low magnetic damping, non-centrosymmetric crystal structure, and rich anisotropies. Here, we report a high-quality half-metallic epitaxial nano-scale thick NiMnSb alloy film grown on a Cr/Ag-buffered MgO (001) single crystalline substrate. High temperature deposition is a crucial parameter for crystal growth and magneto-dynamic properties such as damping, anisotropy, magnetization, etc. After investigating the ferromagnetic resonance (FMR) spectroscopy using a time-resolved magneto-optical Kerr (TRMOKE) microscope and calculating the crystal structure using VESTA and the density of states from first-principles calculations, we discuss how the deposition temperature influences the crystal ordering, damping, and magnetization. Ultralow Gilbert damping with high anisotropic field and saturation magnetization were found for the highly ordered C1b structured nano-scale thick NiMnSb film deposited at 573 K. We also found quite nice agreement between theoretical and experimental data of crystal ordering and damping that explains how the ordering affects the magnetic parameter as well as sample quality. Furthermore, the negative anisotropic magnetoresistance ratio implies the robust bulk half-metallicity. Such unique combination of highly ordered half-metallic NiMnSb alloy in the nano-scale regime with ultralow damping can be regarded as an advantage for applications in spintronic devices.

Influence of carbon nanotubes on thermoelectric properties of p- and n-type Heusler alloys

This paper presents the results of studying the effect of carbon nanotubes on thermoelectric properties of p-type (Nb0.6Ta0.4)0.8Ti0.2FeSb and n-type Ti0.5Zr0.25Hf0.25NiSn half Heusler alloys. The experimental data obtained indicate a strong effect of the carbon nanotubes on electrical conductivity and Seebeck coefficient of the n-type compound, while the changes in these properties in the p-type compound were significantly less. It is suggested that a possible reason for this difference is the formation of a conducting cluster of carbon nanotubes in the sample of the n-type Heusler alloy. Keywords: carbon nanotubes, thermoelectric properties, Heusler alloys, electrical conductivity, Seebeck coefficient.

Влияние углеродных нанотрубок на термоэлектрические свойства сплавов Гейслера p- и n-типа

This paper presents the results of studying the effect of carbon nanotubes on thermoelectric properties of p-type (Nb0.6Ta0.4)0.8Ti0.2FeSb and n-type Ti0.5Zr0.25Hf0.25NiSn half Heusler alloys. The experimental data obtained indicate a strong effect of the carbon nanotubes on electrical conductivity and Seebeck coefficient of the n-type compound, while the changes in these properties in the p-type compound were significantly less. It is suggested that a possible reason for this difference is the formation of a conducting cluster of carbon nanotubes in the sample of the n-type Heusler alloy.

NiMnSn half Heusler alloy: Critical phenomena at the ferromagnetic to paramagnetic phase transition

The critical magnetic analysis and magnetocaloric effect of NiMnSn half Heusler alloy have been explored in this article. This alloy undergoes ferromagnetic to paramagnetic second order phase transition above room temperature at around 388 K. To understand the exchange interaction, magnetic ordering and magnetic phase transition, the critical magnetic analysis has been carried out around the transition temperature. Critical exponents are turned out to be β = 0.44, γ = 1.1 and δ = 3.1. These values imply that the exchange interaction is following towards mean field theory i.e., long-range magnetic ordering is present in the system. The absence of one Ni atom from full Heusler Ni2MnSn alloy does not affect much the magnetic ordering of half Heusler NiMnSn. For environment-friendly solid state cooling applications, the magnetocaloric effect of NiMnSn has been studied. The magnetic entropy change is calculated to be high as 0.81 J/kg-K near the transition temperature for a moderate field change of 30 kOe.

Cobalt based new quaternary Heusler alloys for Spintronic and thermoelectric applications: an Ab-initio study

ABSTRACT In this paper, we employed Density Functional Theory (DFT) to study structural and mechanical stability, electric, magnetic and electronic properties of cubic Co-based new quaternary half-Heusler alloys CoZrCrZ (Z = Al, Ga, In) using WIEN2k. Volume optimisation suggests that these alloys are stable in the Y1 structure and show ferromagnetic behavioTAur. Generalised Gradient approximation calculations confirm the half-metallic nature of the reported alloys, which show metallic nature, and semiconducting band gaps exist in spin-up and spin-down channels, respectively. From the calculated cubic elastic constants, the reported Heusler alloys shows ductile nature. The calculated spin-magnetic moments of CoZrCrZ (Z = Al, Ga, In) are consistent with the Slater-Pauling rule. The very fine narrow band gap in the spin-down channel enhances the thermoelectric properties. The reported ferromagnetic half-metals with good thermoelectric parameters suggests that these alloys have possible applications in spin-based electronics and green energy technology.

Rhodium-based half-Heusler alloys as thermoelectric materials.

Thermoelectric phenomena provide an alternative for power generation and refrigeration, which could be the best solution to the energy crisis by utilizing waste heat energy in the near future. In this study, we have investigated the structural, elastic, electronic, and thermoelectric properties of 18-valence electron count rhodium-based half-Heusler alloys focusing on RhTiP, RhTiAs, RhTiSb, and RhTiBi. The non-existence of imaginary frequencies in the phonon dispersion curve for these systems verifies that they are structurally stable. RhTiP is ductile, while others are brittle. The alloys are semiconducting with indirect band gaps ranging from 0.94 to 1.01 eV. While considering thermoelectricity, we discovered that p-type doping is more favorable in improving the thermoelectric properties. The calculated power factor values with p-type doping are comparable to some of the reported half-Heusler materials. The optimum figure of merit ZT is ∼1 for RhTiBi, and in between ∼(0.38-0.67) for RhTiP, RhTiAs, and RhTiSb. The low thermal conductivities and sufficiently large value of power factor of these alloys suggest that they are promising thermoelectric materials for use in thermoelectric applications.

A mechanistic view of defect engineered VFeSb half-Heusler alloys

Stoichiometric alteration induces characteristic granular defects in VFeSb half-Heusler microstructure.

Structural, electronic and elastic properties of FeCrAs Half-metallic ferromagnetic Half-Heusler Alloy: A First-Principles study

In this work, we employ full potential linearized augmented plane wave approach based on the density functional theory to calculate the structural, electronic, and elastic properties of FeCrAs Half-Heusler compound. For electron exchange, we have considered the most common Generalized Gradient Approximation (PBE-GGA and PBEsol-GGA), as exchange and correlation potential for investigating these properties. The half-metallic ferromagnetic behavior is confirmed by density of states and spin-polarized band structures analysis, which show that the FeCrAs has an indirect band-gap in the spin-down channel and a metallic behaviour in the spin-up channel. Furthermore, the elastic constants (Cij) and the related elastic moduli confirm their stability in the cubic phase and demonstrate their brittle nature. The Debye’s temperature along with compressional, Shear and average elastic wave velocities has also been calculated.[copyright information to be updated in production process]

Alloying Effect on the Lattice Thermal Conductivity of Mnisn Half-Heusler Alloys

Alloying Effect on the Lattice Thermal Conductivity of Mnisn Half-Heusler Alloys

A DFT based analysis of LiYX (X = C, Ge, Si) alloys for energy applications

LiYX (X = C, Ge, Si) half-Heuslar compounds are examined using density functional theory (DFT). WIEN2K kit is used to compute Structural, electronic & optical properties. The full Potential (FP) linearized augmented plane wave (LAPW) technique is used for the calculations. The compounds have optimized lattice parameters in the range 5.7–6.6 Å. The density of states and band structure were also determined and evaluated. The LiYGe and LiYSi alloys have a direct bandgap of 0.68 eV and 0.61 eV at point X, whereas the LiYC compound has an indirect bandgap of 0.48 eV with band transition X → Γ. The optical reflectivity of the alloys is in the ultraviolet region. The high absorption coefficient (>104 cm−1) is obtained. The respective optical conductivity of LiYC, LiYGe, and LiYSi compounds is found to be 7322, 9071, and 8212 in the units of Ohm−1 cm−1 near the UV region. Using real and imaginary parts of the dielectric function, the reflective index, absorption coefficient, electron energy loss, extinction coefficient were also analyzed. Half-Heusler alloys due to their potential applications in solar energy or thermoelectrics are of great interest nowadays. Our results revealed that these compounds are more appropriate candidates for solar and photovoltaic energy applications based on energy bandgap and optical studies. These alloys may act as an alternative to the CdS buffer layer to increase the performance of the device. For experimental fabrications, our computed data may be used as a reference.

A comprehensive computational investigations on the physical properties of TiXSb (X: Ru, Pt) half‐Heusler alloys and Ti2RuPtSb2 double half‐Heusler

AbstractIn this paper, we have investigated the structural, elastic, optoelectronic and thermoelectric properties of the new half‐Heusler alloys TiXSb (X: Ru, Pt) and Ti2RuPtSb2 double half‐Heusler compound, using the full‐potential linearized augmented plane wave method. Different approximations for the exchange‐correlation functional were performed as generalized gradient approximation + Hubbard potential (GGA + U) and its combination with the modified Becke–Johnson potential. The negative values of the calculated formation energy indicate that these compounds are energetically stable. Both half Heusler alloys are half‐metallic ferromagnetic materials and exhibit an integer magnetic moment of Mt = 1.00 μB. While, the Ti2RuPtSb2 is a direct semiconductor at center symmetry. The calculations of optical properties revealed that Ti2RuPtSb2 compound exhibits an excellent optical efficiency. The thermoelectric properties such as the Seebeck coefficient (S); electronic thermal conductivity (κe/τ), power factor (PF), and figure of merit (ZT) have been studied and discussed in detail. Consequently, the investigated compounds were identified as candidate materials for high technological applications.

Theoretical investigations of physical properties of Pt-based half-Heusler alloys PtMnZ (Z = Se, Sn, Te) for spintronic applications

ABSTRACT The structural, mechanical, thermal, electronic and magnetic properties of Pt-based half-Heusler alloys XYZ (X = Pt, Y = Mn, Z = Se, Sn, Te) are determined using FP-LAPW method based on density functional theory (DFT). The exchange–correlation potential is treated with the generalised gradient approximation described by Perdew–Burke–Ernzerhof (PBE-GGA), GGA plus band correlated Hubbard parameter (GGA + U) approximations. Structural results reveal that the PtMnZ half-Heusler alloys (Z = Se, Sn, Te) have metallic character. The negative values obtained for formation energies confirm that our compounds can be synthesised and stabilised experimentally ensuring the stability of these compounds, which is confirmed too by the results of mechanical properties. The thermodynamic ones are also studied through Debye quasi-harmonic model such as Debye temperature and the heat capacity. The calculated electronic properties unveil the metallic nature of the studied compounds. The computed magnetic properties reveal that the total magnetic moment is mainly emanated from the transition metal element. Results suggest that PtMnZ (Z = Se, Sn, Te) compounds are promising candidates for spintronic devices.

First principles study on electronic properties and mechanical stability of HfRhZ (Z = As and Sb) half Heusler alloys

The structural, electronic, elastic and mechanical properties of half-Heusler HfRhZ (Z = As and Sb) alloys are investigated using first principles calculations. The optimized lattice constants, bulk modulus and its pressure derivatives within LDA and GGA approaches are reported. The calculated results of band structure and density of states using GGA and TB-mBJ confirm that HfRhSb is an indirect band gap semiconductor while HfRhAs is a direct band gap semiconductor. The elastic and mechanical properties of HfRhZ (Z = As and Sb) alloys within LDA and GGA approaches are also investigated. The alloys are elastically stable as their elastic constants such as C11,C12 and C44 satisfy the mechanical stability condition. The mechanical properties such as Young’s modulus (E), bulk modulus (B), shear modulus (GH), Poisson’s ratio (σ), the Pugh’s ratio (B/GH), anisotropic factor (A) and Cauchy’s pressure (Cp) are calculated. The studied alloys are ductile in nature, elastically anisotropic and HfRhSb has more stiffness than HfRhAs.

The electronic, half-metallic, elastic, and magnetic properties of new PtWZ (Z = In, Tl, Sn, and Pb) half-Heusler alloys via GGA and GGA+mBJ methods

The first-principle calculations of PtWZ (Z = In, Tl, Sn, and Pb) half-Heusler alloys were calculated by WIEN2k for GGA and GGA+mBJ methods. First, the ferromagnetic (FM) phases were obtained more energetically stable than non-magnetic (NM) and antiferromagnetic (AFM) phases in each alloy. The Curie temperatures of PtWIn, PtWTl, PtWSn, and PtWPb alloys were obtained as 286.98 K, 467.14 K, 721.98 K, and 1114.31 K, respectively, by utilizing the energy differences of the AFM and FM phases. In each method and alloy used, spin-up electrons showed metallic character. In the GGA method, PtW(In, Tl) alloys have direct band gaps of 0.72044 eV and 0.91488 eV in spin-down electrons, while PtW(Sn, Pb) alloys have indirect band gaps of 1.2558 eV and 1.11892 eV, respectively. In the GGA+mBJ method, the bandgap directions in all compounds remained the same. Here, band gaps in PtW(In, Tl, Sn, and Pb) alloys were obtained as 0.99918 eV, 1.15385 eV, 1.42676 eV, and 1.17497 eV, respectively. While the total magnetic moment values of PtW(In, Tl) half-Heusler alloys were obtained as 1.00 μ B/f.u., the total magnetic moments of PtW(Sn, Pb) alloys were obtained as 2.00 μ B/f.u. These results are in full agreement with the Slater-Pauling rule. According to elastic calculations, PtWIn, PtWTl, PtWSn, and PtWPb half-Heusler alloys are elastically stable and ductile.