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A theoretical study of magnetic, electronic structure, mechanical and thermodynamic properties of Cr2TaZ (Z = Al, Ga and Sb) Heusler alloys has been extensively investigated by the full-potential linearized augmented plane wave (FP-LAPW) method with the Generalized Gradient Approximation (GGA). Structural parameters such as lattice constant (a) , bulk modulus (B) and first pressure derivative of bulk modulus (B ,) were obtained by using the Murnaghan equation. The calculated lattice constants for Cr2TaAl, Cr2TaGa and Cr2TaSb alloys are for 61,029, 61,170 and 60,795 Å, respectively. It is found that the L21-type (AlCu2Mnl-type) structure is energetically more stable than the X-type (CuHg2Ti-type) structure due to the lower total energy. The results of elastic constants robustness show that the mechanical stability of Cr2TaZ (Z = Al, Ga and Sb) can be well-maintained. The calculated electronic band structure reveals the metallic nature of Cr2TaZ (Z = Al, Ga and Sb) and its total magnetic moment of 2.00 μ B is mainly contributed by Cr atom from strong spin splitting effect, as indicated with the distinctive distributions of the density of states in two spin directions. Furthermore temperature and pressure dependence of thermodynamic properties of these materials have been examined in the ranges (0–1400 K) and (0–25 GPa), respectively. [ABSTRACT FROM AUTHOR]

We present the theoretical and experimental results for the full Heusler alloys Mn2MAl for late 3d transition metals – M = Fe, Co, Ni. For the first time, the synthesized Mn2CoAl and Mn2NiAl alloys crystallize in the β-Mn- and B2-types crystal structure. The electronic structure and magnetic properties of the alloys were investigated within the framework of first-principles theoretical calculations. It was revealed that the alloys have metallic properties and antiparallel alignment of the large Mn magnetic moments and almost compensated total magnetic moments. In addition, we investigated the effect of electronic correlations on the electronic structure and magnetic properties of the alloys within DFT + U method that resulted in a negligible effect for the total magnetic moments of Mn2MAl (M = Fe, Co, Ni). The frequency dependence of the real and imaginary parts of the dielectric constant is measured in the spectrum region of 0.1–5 eV. In order to characterize thermoelectric properties of the studied Heusler alloys, we performed measurements of electrical resistivity and calculated Seebeck coefficient. The results are interpreted based on our theoretical calculations and different structural compositions. [ABSTRACT FROM AUTHOR]

In this work, we report on CoMnSi half‐Heusler alloy as a cathode material for secondary lithium‐ion batteries using ab initio methodology based on the density functional theory. The first‐principle calculations have been performed via the Wien2k package, which utilizes the full potential linearized augmented plane wave (FP‐LAPW) method to estimate the stability of the proposed structures and electronic characteristics while considering the exchange and correlation effects within the generalized gradient approximation. This alloy is found structurally stable with better electronic properties and with the alloying of lithium (Li) into the host lattice of CoMnSi, the metallic character is attained for LixCo1−xMnSi (0.125 ≤ x ≤ 1). We propose possible reactions at electrodes during the electrochemical lithiation. The addition of Li in place of the Co atom is found to be an endothermic process. With the increase in lithium concentration, a substantial change in the total and atom projected density of states around the Fermi level is observed. The theoretical maximum specific capacity (CM) and theoretical open circuit voltage (OCV) increase with the increase of lithium concentration in CoMnSi. The CM and OCV values attain a maximum value of around 297 mAh/g and 2.4 Volts for x ≥ 0.75, which means towards the complete conversion of CoMnSi into LiMnSi. The LiMnSi exhibits a similar structure as CoMnSi, which is also advantageous for the overall performance of lithium‐ion batteries to avoid any volumetric change during the charging and discharging cycles. Hence, the proposed half‐Heusler alloys have great potential to be used as a cathode material for lithium‐ion batteries. [ABSTRACT FROM AUTHOR]

Using first-principles calculations based on density-functional theory, this paper investigates the electronic structure and magnetic properties of the Heusler alloy Mn2LiGe bulk and its (001) surfaces. The Mn2LiGe bulk is demonstrated to be inverse Heusler alloy with space group of F43m and lattice constant of 5. 87 Å. A direct band gap with a width of 1. 1 eV near the Fermi surface of the spin-down channel is detected. The Mn2LiGe bulk possesses stable half-metallic and magnetism in the lattice constant range of 5. 55 - 6. 33 Å. In addition, six different surface structures of Mn2LiGe are constructed in this paper. The first layer atoms on the surface undergo different displacements, increasing the surface roughness. Due to surface effects, the magnetic properties of atoms on the surface are different compared to those in the bulk. Both the MnA MnA and MnB MnB surface structures have the highest magnetic moments, while the LiLi and the GeGe surface structures have the lowest magnetic moments. Electronic structure calculations show that the half-metallic band gap present in the bulk is destroyed in all six surface structures and the spin polarization is weakened in varying degrees. Only the LiLi surface structure maintains up to 99. 9% of the surface spin polarization, making the surface an excellent prospect for applications in spintronic devices. [ABSTRACT FROM AUTHOR]

We investigate the effects of off-stoichiometric compositional variations from the Co2Fe(Ga0.5Ge0.5) (CFGG) full-Heusler alloy on its half-metallic electronic structure. First-principles calculations predict that the Co antisite defects that occupy Fe-sites (CoFe) lead to a finite DOS in the half-metallic gap of CFGG. Fe antisites defects in Co-sites (FeCo) introduced by excessing Fe composition, which could suppress the formation of CoFe, preserves the half-metallic gap but reduces spin polarization because the Fermi level shifts to the lower energy. We found that, in Fe-excess CFGG, Ge-excess has an important role to enhance the spin polarization by lifting up the Fermi level position and suppressing the formation of CoFe. To confirm the effect of the Fe and Ge-excess off-stoichiometric composition on spin polarization and phase-purity experimentally, we fabricated CFGG epitaxial thin films with various composition ratios (Co2−αFe1+α) (Ga1−βGeβ)1+γ with small positive γ (=0.09–0.29). It turns out that Co1.75Ge or Fe1.7Ge secondary phase often forms in the films for β ≥ 0.69 in Fe-deficient (α ≤ 0.21) and excess (α ≥ 0.49) compositions. This secondary phase can be suppressed by tuning the Ge and Fe compositions, and the L21-phase pure film was found in Co39.4Fe29.3Ga13.4Ge17.9 (α = 0.28 , β = 0.57 , γ = 0.25). The measurements of conventional magnetoresistance effects qualitatively indicate higher spin polarization in the Co39.4Fe29.3Ga13.4Ge17.9 film compared to other Co-excess and Ge-deficient films, which evidences the benefit to make Fe- and Ge-excess off-stoichiometric CFGG for obtaining the half-metallic nature of CFGG. [ABSTRACT FROM AUTHOR]

The stabilities, mechanical, electronic, and magnetic properties of the new equiatomic quaternary Heusler alloy (EQHA) RuTiCrSi were investigated using the Kohn‐Sham DFT (KS‐DFT) calculations within the generalized gradient approach (GGA), the modified version of the exchange potential introduced by Becke and Johnson in addition to the GGA (mBJ‐GGA), and Heyd‐Scuseria‐Ernzerhof (HSE06) hybrid functional. The ground‐state equilibrium energy reveals that the ferromagnetic with type 2 structure is the more stable. The RuTiCrSi is energetically, mechanically, and dynamically stable. The calculated self‐consistent total magnetic moment is 2 μB and agrees well with the Slater‐Pauling rule of Mt=Zt−24$$ {M}_{\mathrm{t}}=\left|{Z}_{\mathrm{t}}-24\right| $$. The electronic structure results from mBJ‐GGA and HSE06 functionals show a half‐metallic behavior. A high Curie temperature is obtained using the mean‐field approximation. The thermoelectric response was calculated using the semi‐classical Boltzmann transport equation under constant relaxation time. The maximum value of Seebeck coefficient is observed at the ambient temperature of 741μVK−1$$ 741\ \upmu \mathrm{V}\ {\mathrm{K}}^{-1} $$. It was also observed that the power factor increases significantly as temperature rises. Therefore, the new EQHA RuTiCrSi seems to be a potential candidate for spintronic thermoelectric applications. [ABSTRACT FROM AUTHOR]

In this study, we investigate the structural, electronic, magnetic and mechanical properties of the Na-based half-Heusler alloys XYZ composed of X=Na ( p 0 atom); Y=K, Rb, Cs ( d 0 atoms) and a main body sp atom Z=C, Si, Ge, Sn, Pb by using the DFT based full-potential WIEN2k package. We compare the total energy vs volume of ferromagnetic, antiferromagnetic and non-magnetic half-Heusler structures to obtain the stable magnetic structure. Calculations show that compounds are stable in the half-Heusler β -phase and the ferromagnetic state. From 15 alloys under study, 13 of them showed half-metallic behavior in the minimum-energy half-Heusler phase at the optimized lattice constant. We show that all compounds have the same total magnetic moment equal to 2 μ B . The band structure and the density of states of half-Heusler alloys are obtained. The elastic constants C 11 , C 12 and C 44 of the single crystal and the related elastic moduli G, B, E, υ of the polycrystalline aggregates are also calculated and used to study the mechanical stability of these alloys. Furthermore, the average, transverse, longitudinal sound velocities and the Debye temperature for these compounds are calculated. Finally, the Curie temperatures T C of the half-Heusler alloys are estimated by using the mean field approximation. The estimated Curie temperatures shows that these compounds preserve the ferromagnetic state and magnetic polarization at temperatures much higher than the room temperature and may be suitable for spintronic applications. [ABSTRACT FROM AUTHOR]

Studies of the electronic structure and optical properties of the GdNiSb half-Heusler alloy have been performed. Calculations of the total and partial densities of electronic states were carried out on the basis of the GGA + U method, taking into account the correction for strong interactions in the f-electron system of gadolinium ions. By the method of spectral ellipsometry in the range of 0.078–5.64 eV, the dielectric functions of the alloy are investigated, their dispersion features are revealed. The anomalous behavior of optical conductivity in the infrared region of the spectrum for metals was found, confirming the presence of an energy gap at the Fermi level in the electronic spectrum, predicted in the calculation. A comparative analysis of the experimental and theoretical frequency dependences of optical conductivity is carried out, the features of interband light absorption are identified. The plasma frequency of conduction electrons is determined. [ABSTRACT FROM AUTHOR]

Magnetic, transport, and optical properties of thin film and bulk Fe 2 CrGa alloy samples with different types of atomic order were experimentally investigated. The obtained data were discussed in terms of first-principle calculation results made for the stoichiometric Fe 2 CrGa alloy with different types of atomic order and disorder. An ultimate atomic disorder in Fe 2 CrGa alloy films was obtained by employing vapor quenching deposition onto substrates cooled by liquid nitrogen. Annealing of as-quenched Fe 2 CrGa alloy films causes their crystallization at T a n n = 750 K with the formation of the disordered A2-type structure, which is accompanied by the rapid growth of alloy resistivity in a narrow temperature range, formation of multi-phase magnetic structure and changes in the optical properties. Crystalline bulk and film Fe 2 CrGa alloy samples show the dome-like temperature dependence of the resistivity with maximums near their Curie temperatures and explained in terms of competition between negative with temperature contribution from highly resistive media and positive from the electron–magnon scattering. The big resemblance between calculated for Hg 2 CuTi type of atomic order and experimental optical conductivity spectra for annealed Fe 2 CrGa alloy films proves that Hg 2 CuTi type of atomic order is more probable for this alloy. [ABSTRACT FROM AUTHOR]

Information on the energy, charge, and spin characteristics of Pd1-xMexMnSn alloys (Me = Co, Ni, x = 0.0--1.0) is obtained using band calculations within the FLAPW (full-potential linearized augmented-plane-wave) model. As determined, an increase in the concentration of the cobalt or nickel atoms leads to an increase in the interatomic electron density inside the alloys. This results in both a concurrent reduction in the parameters of their crystal lattices and an increase in the binding energies of the atoms. The number of electrons Q within the atomic spheres of Pd, Mn, and Sn in cobalt-containing alloys exceeds the corresponding values for nickel-containing phases, and the dependences of Q exhibit a systematic tendency to increase with the growth of substitutional- atoms' concentrations. The observed polarization of valence electrons leads to the appearance of magnetic moments on the atoms of the alloys. The magnetic moments of metal atoms are ferromagnetically ordered, and their magnitude depends on the type and concentration of substitutional atoms. [ABSTRACT FROM AUTHOR]

In this paper, we investigated the structural and magneto-electronic properties, and exchange coupling in new vanadium (V)-doped PbTiO3 perovskite oxide such as PbTi1−xVxO3 compounds with compositions of x = 0, 0.25, 0.5, 0.75, and 1. The calculations of these properties are based on density functional theory using the generalized gradient approximation of Wu-Cohen (GGA-WC) and the Tran-Blaha-modified Becke–Johnson potential (TB-mBJ). Our calculations with GGA-WC revealed that the lattice constant for PbTiO3 is in good concordance with other theoretical and experimental results, while for PbTi1−xVxO3 at x = 0.25, 0.5, 0.75, and 1, the lattice constant decreases with increasing vanadium concentration owing to the difference in sizes of Ti and V ionic radii. The improved electronic structures obtained by employing the TB-mBJ potential, demonstrated that the half-metallic ferromagnetic and half-metallic gaps are present in PbTi1−xVxO3 materials at x = 0.25, 0.5, 0.75, and 1, which makes them promising candidate materials for spintronics applications. [ABSTRACT FROM AUTHOR]

By using density functional theory, we have explored the structural, electro-mechanical, thermophysical and thermoelectric properties of CoZrSi and CoZrGe Heusler alloys. The ground state stability was determined by optimising the energy in various configurations like type I, II, and III. It was found that these alloys stabilized in the ferromagnetic phase in type I. We employed the Generalised Gradient Approximation and modified Becke-Johnson potentials to explore the electronic structure. The band structures of each of these Heusler alloys exhibit a half-metallic nature. Additionally, the computed second-order elastic parameters reveal their ductile nature of them. To understand the stability of the alloys at different pressures and temperatures, we investigated various thermodynamic parameters using the Quasi-Harmonic Debye model. We obtained the transport coefficients using the Boltzmann theory. Our findings indicate that these alloys can be used in spintronics and thermoelectric domains. [ABSTRACT FROM AUTHOR]

In the present work, we study the geometric, electronic, magnetic and mechanical properties of Co-based full Heusler alloys Co2TaZ (where Z = Si and Sn). Structural optimization and physical properties have been investigated using density functional theory (DFT) calculations. While calculating electronic and magnetic properties, the GGA+U scheme, where U is the Hubbard term, predicts more efficient results than the generalized gradient approximation (GGA). The calculated electronic band structure and density of states (DOS) with spin magnetic moment reveal the half-metallic character of both alloys. The total computed magnetic moment amounts to a nearly integral value of 3 μB for Co2TaSi and Co2TaSn. It has been found that these alloys obey the Slater–Pauling rule. The calculated values of elastic constants indicate that these alloys are mechanically stable, difficult to compress and ductile. The high spin polarization at the Fermi level in these alloys makes them useful for spintronic applications. [ABSTRACT FROM AUTHOR]

Abstract—Magnetic properties and electronic structure inherent in FeRhSn1 − xZx alloys (x = 0, 0.25, 0.5, 0.75, 1) have been studied with the use of first-principles methods in an environment of a VASP software package. It is shown that the γ-phase is energetically favorable in the case of all the alloys, except for the FeRhSi alloy, for which the β-phase is the equilibrium one. It has been shown that the addition of a fourth element to a three-component alloy leads to a change in the position of the valence band and conduction band with respect to the Fermi level, which makes it possible to obtain novel four-component alloys exhibiting an entirely overwhelming spin polarization. It is shown that the FeRhSn1 − xGex alloy (x = 0, 0.25, 0.5, 0.75, 1), FeRhSn1 − xSix alloy (x = 0, 0.25, 0.5, 0.75), and FeRhSn1 − xSbx alloy (x = 0, 0.25) represent halfmetallic ferromagnets. [ABSTRACT FROM AUTHOR]

Computer simulations within the framework of density functional theory are performed to study the electronic, dynamic, elastic, magnetic, and thermoelectric properties of a newly synthesized FeRhCrGe alloy and a theoretically predicted FeRhCrSi alloy. From the electronic structure simulations, both FeRhCrZ (Z = Si and Ge) alloys at their equilibrium lattice constants exhibit half-metallic ferromagnetism, which is established from the total magnetic moment of 3.00 μB, and that the spin moment of FeRhCrGe is close to the experimental value (2.90 μB). Their strength and stability with respect to external pressures are determined by simulated elastic constants. The Debye temperatures of FeRhCrSi and FeRhCrGe alloys are predicted to be 438 K and 640 K, respectively, based on elastic and thermal studies. The large power factors (PFs) of the two investigated alloys are in contour with those of the previously reported Heusler compounds. Besides, the conservative estimate of relaxation time speculated from the experimental conductivity value is 0.5 × 10−15 s. The room temperature PF values of FeRhCrSi and FeRhCrGe compounds are 2.3 μW/cm K2 and 0.83 μW/m K2, respectively. Present investigations certainly allow the narrow bandgap, spin polarization, and high PF values to be looked upon for suitable applications in thermoelectrics and spintronics. [ABSTRACT FROM AUTHOR]

Oxygen reduction reactions (ORRs) involve a multistep proton-coupled electron process accompanied by the conversion of the apodictic spin configuration. Understanding the role of spin configurations of metals in the adsorption and desorption of oxygen intermediates during ORRs is critical for the design of efficient ORR catalysts. Herein, a platinum–rare-earth-metal-based alloy catalyst, Pt2Gd, is introduced to reveal the role of spin configurations in the catalytic activity of materials. The catalyst exhibits a unique intrinsic spin reconfiguration because of interactions between the Gd-4f and Pt-5d orbitals. The adsorption and desorption of the oxygen species are optimized by modifying the spin symmetry and electronic structures of the material for increased ORR efficiency. The Pt2Gd alloy exhibits a half-wave potential of 0.95 V and a superior mass activity of 1.5 A·mgPt−1 in a 0.1 M HClO4 electrolyte, as well as higher durability than conventional Pt/C catalysts. Theoretical calculations have proven that the spin shielding effect of Gd pairs increases the spin symmetry of Pt-5d orbitals and adsorption preferences toward spin-polarized intermediates to facilitate ORR. This work clarifies the impact of modulating the intrinsic spin state of Pt through the interaction with the local high spin 4f orbital electrons in rare-earth metals, with the aim of boosting the spin-related oxygen reduction reaction, thus fundamentally contributing to the understanding of new descriptors that control ORR activity. [ABSTRACT FROM AUTHOR]

Co 2 FeSi Heusler alloys have attracted a lot of attention due to their interesting properties for various technological applications. In this study, we present the results of ab-initio calculations of the electronic, structural and magnetic properties using generalized gradient approximations (GGA and GGA + U). The energies obtained from GGA are used to calculate the magnetic coupling and establish an effective Hamiltonian. Additionally, we utilized mean-field theory and Monte Carlo simulation to evaluate physical properties such as magnetization, susceptibility and critical exponent of the material from the effective Hamiltonian. The results indicate that Co2FeSi, which exhibits a half-metallic behaviour, may be suitable for use in spintronic applications. [ABSTRACT FROM AUTHOR]

Electronic structures, and the magnetic and half-metallic (HM) properties of equiatomic quaternary ScRhTiZ (Z = Si, Ge, Sn) Heusler (EQH) alloys have been analyzed by first-principles calculations. The results show that equilibrium lattice constants of ScRhTiZ (Z = Si, Ge, Sn) are 6.29 Å, 6.36 Å, and 6.61 Å, respectively. For uniform strain, HM properties are observed with magnetic moments of 2 μB in the range of lattice constants of 5.51–6.28 Å, 5.48–6.29 Å, and 5.44–6.26 Å for ScRhTiZ (Z = Si, Ge, Sn), respectively. For tetragonal distortion, the transitions of FM (metal ferromagnetic)-HM-FM-HM-FM states can be obtained for ScRhTiSi by changing the c/a. ScRhTiGe exhibits an FM state and ScRhTiSn undergoes the transitions of FM-FIM (ferrimagnetic)-FM states in its metal nature. Magnetic moments mainly come from Sc and Ti atoms. All three compounds obey the Slater–Pauling rule, Mt = Zt − 18 in HM nature. The phonon spectra indicate that ScRhTiGe and ScRhTiSn are dynamically stable at equilibrium lattice constants due to no imaginary frequencies. This work can facilitate the exploration of new HM materials in the future application of spintronic devices. [ABSTRACT FROM AUTHOR]

By employing the full-potential linearized augmented plane wave (FP-L/APW + lo) technique based on density functional theory (DFT), the structural, electronic and magnetic properties of zincblende W (1 − x) AgxGe alloys (x = 0 and 0.25) are scrutinized thoroughly. Based on the generalized gradient approximation (GGA), the exchange-correlation energy functional is included in the current simulation. For computing the structural features, the GGA approximation is applied, whereas GGA, GGA + U and the modified Burke–Johnson of GGA + U (TB-mBJ- GGA + U) approximations are incorporated to perform the calculations of electronic and magnetic behaviors of these alloys. The structural analysis of the alloys indicated that the total energy of the W 0. 7 5 Ag 0. 2 5 Ge alloy was favorable in the ferromagnetic ground state. The spin-polarized electronic structure shows the half-metallic behavior of the W 0. 7 5 Ag 0. 2 5 Ge alloy, while the WGe compound is identified as a metal. The magnetic results obtained from the half-metallic W 0. 7 5 Ag 0. 2 5 Ge alloy increasingly support the full half-metallicity of this compound because an integer value is acquired for the total magnetic moment. The strong hybridization between 4p-Ge and 3d-W states brings forth weak local magnetic moments at the nonmagnetic Ge atomic sites and reduces the local magnetic moment of the W atomic sites from its free space charge. [ABSTRACT FROM AUTHOR]

The structural, electronic, thermal and lattice thermal transport properties of the three hypothetical quaternary Heusler alloys FeRuTiX (X=Si, Ge, Sn) were investigated with the aid of first‐principles calculations. All compounds were found to be semiconducting with a small indirect band gap. Flat bands near the conduction band edge and degenerate multi‐bands near the valance band edge suggest that these systems should exhibit both large Seebeck coefficients and good electrical conductivity. The analysis of the calculated vibrational spectra showed that the three compounds are thermodynamically stable. The computed lattice thermal conductivity indicates that among the three compounds that of FeRuTiSn is rather low at high temperature. Indeed, a low lattice thermal conductivity (∼3.5 Wm−1 K−1 at 1000 K) together with a small electronic band gap (0.51 eV) with an appropriate electronic structure (disperse and flat bands) render FeRuTiSn a promising candidate as a high‐temperature thermoelectric material. [ABSTRACT FROM AUTHOR]

CsSe is reported as a half‐metallic ferromagnet compound which is optimized using the first principle calculation, but it is yet to prepared experimentally. CsCl‐type and NaCl‐type structures are preferred in literature to form from their electronic structures. Whether these two structures physically withstand or not is still unclear. Their mechanical properties can give a clear picture. The present study works in this direction and uncovers the mechanical perspective using DFT (Density Functional Theory) framework. The elastic stiffness tensor is obtained first, evaluated the mechanical parameters and then revealed how the mechanical formation is possible. Overall study elucidates to the evidence of why the CsSe compound occurs in CsCl‐type and how it has withstood at a room temperature using the elastic and mechanical properties through DFT. The stability of CsCl‐type has been confirmed from the phonon dispersion by DFPT (Density Functional Perturbation Theory) in this paper. The study also conducted the examination of the CsCl‐type's spintronic nature. [ABSTRACT FROM AUTHOR]

In this study, the all-d-metal Heusler compounds Ni2MnT (T = Sc, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, and W) were considered as representative examples, and the magnetism-dependent martensitic phase transition was systematically investigated by first-principles calculations. Comparative analysis of the calculated magnetic states-dependent elastic parameters, electronic structures, and thermodynamic parameters indicates that weakly magnetic Ni2MnT compounds with late transition metal atoms show higher possibilities of martensitic phase transition. Although magnetism is not the necessary condition for martensitic phase transition, the strong magnetic moment in Ni2MnT compounds with early transition metal atoms can suppress the occurrence of martensitic phase transition. When the magnetism is absent or becomes weak, the suppressed martensitic phase transition can be re-evoked. The current study indicates that magnetism plays an important role in determining the martensitic phase transition in all-d-metal Heusler compounds Ni2MnT. Careful control of the magnetism can serve as another parameter to tune martensitic phase transition in Ni−Mn-based all-d-metal Heusler compounds. This study can be helpful to explore and design outstanding candidate materials for solid-state refrigeration applications based on the martensitic phase transition. [ABSTRACT FROM AUTHOR]

In this work, the electronic structure and optical behavior and the thermoelectric performance of the known HfNiSn compound have been studied under the substitution of Mn transition metal instead of Ni atoms. Necessary calculations are performed in the framework of DFT first principles studies by applying generalized gradient approximation (PBE-GGA) as well as solving Boltzmann's semi-classical equations. The entering Mn leads to a change in the electronic structure of HfNiSn and the occurrence of half-metallic ferromagnetic behavior with 100% polarization at the Fermi level. The maximum ZT value obtained for HfMnSn shows that HfNiSn would be suitable for thermoelectric applications at room temperature, both in pure and Mn presence. The examination of optical parameters also indicates good absorption in the visible range for this compound in all cases. [ABSTRACT FROM AUTHOR]

The results of calculations of the electronic structure, thermoelectric characteristics, and experimental study of the thermoelectric, electrical, and optical properties of Mn2MeAl Heusler alloys (Me = Ti, V, Cr) are presented. The agreement between theory and experiment in the sign of the Seebeck coefficient is shown. The obtained pattern of the band spectrum allows us to qualitatively explain the peculiarities of the temperature dependences of the electrical resistance and the permittivity dispersion. [ABSTRACT FROM AUTHOR]

In this theoretical study, we investigate the effect of electron correlations on the electronic structure and magnetic properties of the full Heusler alloy Mn 2 NiAl in the framework of first-principles calculations. We investigate the electron correlation effect as employed within hybrid functional (HSE) and also within the DFT+U method with varied values of parameters between 0.9 and 6 eV. The XA-crystal structure was investigated with antiferromagnetic orderings of the magnetic moments of the manganese. It was found that with a growth of the Coulomb interaction parameter, the manganese ions magnetic moment increases, and it reaches the value of 4.15–4.46 μ B per Mn. In addition, the total magnetic moment decreases because of the AFM ordering of the Mn ions and a small magnetic moment of Ni. The calculated total magnetic value agrees well with recent experiments demonstrating a low value of magnetization. This experimental value is most closely reproduced for the moderate values of the Coulomb parameter, also calculated in constrained LDA, while previous DFT studies substantially overestimated this value. It is also worth noticing that for all values of the Coulomb interaction parameter, this compound remains metallic in its electronic structure in agreement with transport measurements. [ABSTRACT FROM AUTHOR]

Heusler compounds have generated significant interest in spintronics due to their unique features. The structural stability, electronic structure, magnetic, and elastic properties of Heusler alloys VXRh2 (X = Sn, Ge, and Si) are investigated using first‐principles calculations of density functional theory in the Quantum Espresso code. The alloys exhibit three magnetic states (nonmagnetic, ferromagnetic, and ferrimagnetic) and several structural phases (face centered cubic (FCC) and tetragonal). It is found that pressures below 0 GPa produce the FCC phase, while greater pressures produce two tetragonal phases. VSnRh2 is a ferromagnetic metal, while VSiRh2 and VGeRh2 exhibit excellent half‐metallic ferromagnetism. The equilibrium lattice constants of VSiRh2 and VGeRh2 are stable against changes, making these Heusler alloys ideal for spintronic devices. Elastic constant computations show that compounds are mechanically stable. [ABSTRACT FROM AUTHOR]

We investigate the Li2CuSb full‐Heusler alloy using the first‐principles electronic structure calculations and propose the electrochemical lithiation in this alloy. Band structure calculations suggest the presence of metallic nature in this alloy contrary to half‐metallic nature as predicted for most of the members of the full‐Heusler alloy family. This alloy is found to be a promising anode material for high‐capacity rechargeable batteries based on lithium‐ion. We found a removal voltage of ≈ 2.48 V for lithium ions in the Li2CuSb/Cu cell, which is in good agreement with the experimentally obtained result for a similar kind of material Cu3Sb. During charge and discharge cycles of the Li2CuSb/Cu cell, the formation of a non‐stoichiometric compound (Li2−yCu1+xSb) having a similar structure as Li2CuSb suggests a better performance as well as stability of this cell. [ABSTRACT FROM AUTHOR]

In this paper, we present the calculation results of the electronic structure and optical spectrum and an experimental study of the optical properties of Heusler alloys Mn2 –xFe1 +xAl (x = –0.5, 0, 0.5, 1). An anomalous for metallic systems behavior of the optical conductivity of alloys in the IR region of the spectrum was found: the absence of Drude growth and a high level of interband absorption. This behavior is shown to be determined by the features of the electronic structure: the Fermi level is located in the region of high density of states that is formed by the d states of Mn and Fe. [ABSTRACT FROM AUTHOR]

In this paper, the band structure and spin polarization of Co2MnSi1-xZx（Z=B, P, As） Heusler alloys are studied by first principles calculations. It is also demonstrated that the substitution of Si by other elements Z with different valence electrons can control the movement of Fermi level in the band gap. At the same time, the lattice parameters have a near-linear variation with the concentration x of the Z element, and the band structures of these alloys have similar characteristics. The magnetic moments of different compounds show a linear trend with the number of valence electrons, which is consistent with the Slater-Pauling behavior. The calculated results show that the Co2MnSi1-xPx and Co2MnSi1-xAsx alloys have better electronic properties and higher spin polarization when x=0.125. [ABSTRACT FROM AUTHOR]

This paper presents electronic spectrum calculations and a study of the optical properties of the binary compounds Mn70Al30 and Mn80Al20 with the β-Mn structure. The energy dependences of the calculated density of states, with high values at the Fermi level, are determined by broad bands formed by manganese 3d states. The calculated electronic structures are used to analyze measured optical conductivity spectra of the alloys in the quantum light absorption range. From their optical properties in the infrared spectral region, we evaluate a number of characteristics of conduction electrons. [ABSTRACT FROM AUTHOR]

Using the full-potential linearized augmented plane wave plus local orbital method based on spinpolarized density functional theory, we investigate the parameters of the structure, the electronic, magnetic, and thermodynamic properties of cubic zinc-blende Cd0.75Cr0.25Se and Zn0.75Cr0.25S ordered ferromagnetic materials. We adopt the Perdew–Burke–Ernzerhof generalized gradient approximation and the modified Becke–Johnson exchange potential for the exchange-correlation energy and potential. Furthermore, the effect of high pressure on the normalized unit cell volume, bulk modulus, and Grüneisen parameter for both CdSe and ZnS binary compounds as well as for Cd0.75Cr0.25Se and Zn0.75Cr0.25S partially substituted materials was also predicted. The results indicate that both these materials are stabilized in the ferromagnetic phase. Using the modified Becke–Johnson approach and Perdew–Burke–Ernzerhof generalized gradient approximation, our calculations also demonstrate that both Cd0.75Cr0.25Se and Zn0.75Cr0.25S alloys are semiconductors with the magnetic moment of 4 µB per formula unit. Furthermore, the calculations of the s–d exchange constant and p–d exchange constant clearly indicate the magnetic nature of these compounds. Finally, in order to gain further information, basic thermodynamic properties such as heat capacity, thermal expansion coefficient, and entropy have been explored using the quasi-harmonic Debye model. [ABSTRACT FROM AUTHOR]

The structural, electronic, and magnetic properties of a new series CoRhZrZ quaternary Heusler were investigated theoretically by using the density of function theory calculation. All the compounds were found to be stable at the ferromagnetic phase. The magnetic moments of the compound show a positive value ranging from 1 to 2 μB. In addition, the electronic structure of CoRhZrSi shows a large value of the half‐metallic band gap of 0.34 eV. This reflects the high thermal stability of the compound at high temperatures and allowing for a wide range of applications of this material in varying domains, especially those requiring high thermal stability such as the oil and gas sectors, geological applications, and space applications. [ABSTRACT FROM AUTHOR]

Due to growing interest to predict and design new potential Heusler alloys by using theoretical calculations and highly functional software, research on Heusler alloys has taken great attention. From this point of view, this study considers investigation of X2MgAl (X = Sc, Ti and Y) alloys by adopting first principles calculations for the first time. A thorough investigation has been carried out to reveal these alloys' mechanical, electronic, vibrational and thermodynamic properties. It is seen that all alloys have negative formation energies as − 0.278 eV/atom for Sc2MgAl, − 0.058 eV/atom for Ti2MgAl and − 0.304 eV/atom for Y2MgAl which indicates synthesisability and thermodynamic stability. Mechanical stability investigations based on the elastic constants of alloys have revealed that all alloys are mechanically stable. The electronic band structures of alloys demonstrate that X2MgAl (X = Sc, Ti and Y) alloys are metallic since there is no energy gap near the Fermi level. Cauchy's pressures of alloys are found as − 17.791 GPa for Sc2MgAl, 31.404 GPa for Ti2MgAl and − 11.759 GPa for Y2MgAl which displays that Sc2MgAl and Y2MgAl are brittle and Ti2MgAl is ductile. The phonon dispersion curves are calculated along the lines of high symmetry within the first Brillouin region. Phonon frequencies are completely positive in the full Brillouin region, which proves the dynamic stability of the L21 phases of these alloys. Several thermodynamic properties such as Debye entropy, temperature and vibrational free energy are also computed and analysed. Debye entropies of alloys follow Ti2MgAl > Y2MgAl > Sc2MgAl relationship. [ABSTRACT FROM AUTHOR]

First-principles calculations of the stability, electronic, and magnetic properties of full-Heusler compound V2FeSi and Fe2VSi in regular ( L 2 1 ) and inverse ( X A ) structures have been performed using density functional theory within an SCAN meta-GGA functional. It is found that the X A crystal lattice is energetically more favorable for V2FeSi, while Fe2VSi forms the L 2 1 structure. In both cases, the electronic structure of the energetically stable modifications corresponds to half-metallic ferrimagnets. Magnetic properties of energetically favorable structures obey the Slater–Pauling rule. All considered properties of the studied structures are explained within the crystal orbital Hamilton population analysis. [ABSTRACT FROM AUTHOR]

We investigated Heusler-type Ru2VAl, a candidate material for next-generation thermoelectric conversion, by first-principle calculations of its thermoelectric conversion properties and direct experimental observations of its electronic structures, employing photoemission and infrared spectroscopy. Our results show that Ru2VAl has a wider pseudogap near the Fermi level compared to Fe2VAl. Accordingly, a higher thermoelectric conversion performance can be expected in Ru2VAl at higher temperatures. [ABSTRACT FROM AUTHOR]

In this theoretical study, we investigate the effect of electron correlations on the electronic structure and magnetic properties of the full Heusler alloy Mn2NiAl in the framework of first-principles calculations. We investigate the electron correlation effect as employed within hybrid functional (HSE) and also within the DFT+U method with varied values of parameters between 0.9 and 6 eV. The XA-crystal structure was investigated with antiferromagnetic orderings of the magnetic moments of the manganese. It was found that with a growth of the Coulomb interaction parameter, the manganese ions magnetic moment increases, and it reaches the value of 4.15–4.46 μB per Mn. In addition, the total magnetic moment decreases because of the AFM ordering of the Mn ions and a small magnetic moment of Ni. The calculated total magnetic value agrees well with recent experiments demonstrating a low value of magnetization. This experimental value is most closely reproduced for the moderate values of the Coulomb parameter, also calculated in constrained LDA, while previous DFT studies substantially overestimated this value. It is also worth noticing that for all values of the Coulomb interaction parameter, this compound remains metallic in its electronic structure in agreement with transport measurements.

This paper presents the strain effects on the structural, electronic and phonon properties of a newly proposed SrBaSn half Heusler compound. Since it is stable considering chemical thermodynamics, we tested its strength against uniform strain w.r.t phonon spectrum and it produces a direct bandgap of 0.7 eV. The direct bandgap reduces to 0.19 eV at −12% strain beyond which the structure is unstable. However, an indirect gap of 0.63 eV to 0.39 eV is observed in the range of +5% to +8% strain and afterwards the strain application destabilizes the structure. From elastic parameters, the ductile nature of this material is observed. [ABSTRACT FROM AUTHOR]

In 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. [ABSTRACT FROM AUTHOR]

We investigate the high temperature thermoelectric properties of Heusler alloys Fe2-xMnxCrAl (0=x=1). Substitution of 12.5% Mn at Fe-site (x = 0.25) causes a significant increase in high temperature resistivity (ρ) and an enhancement in the Seebeck coefficient (S), as compared to the parent alloy. However, as the concentration of Mn is increased above 0.25, a systematic decrement in the magnitude of both parameters is noted. These observations have been ascribed (from theoretical analysis) to a change in band gap and electronic structure of Fe2CrAl with Mn-substitution. Due to absence of mass fluctuations and lattice strain, no significant change in thermal conductivity (Kl) is seen across this series of Heusler alloys. Additionally, S drastically changes its magnitude along with a crossover from negative to positive above 900 K, which has been ascribed to the dominance of holes over electrons in high temperature regime. In this series of alloys, S and ρ shows a strong dependence on the carrier concentration and strength of d-d hybridization between Fe/Mn and Cr atoms. [ABSTRACT FROM AUTHOR]

The electronic structure and optical properties of the Heusler alloys Co2NiGa, Co2NiAl, Co2FeGa, and Co2FeAl are reported and compared in this work. In the Fe-based alloys, Co2FeGa and Co2FeAl, the electronic structure is found to have 100% spin polarization with the indirect energy gap in the Γ - X direction, whereas in Co2NiGa and Co2NiAl, the density of states is metallic in both spin projections with spin polarization of 55% (Co2NiGa) and 37% (Co2NiAl). Total and Co partial magnetic moments of all Heusler alloys for the optimized lattice parameters were found in a good agreement with previous calculations and experimental data. The frequency dependence of the real and imaginary parts of the complex dielectric constant for the Heusler alloys is studied in the spectrum region of 0.08–5 eV. The research results are discussed based on the performed calculations of the electronic structure. It was found that the character of variations of the spectral parameters of the alloys is typical for media with the metallic conductivity. In the IR region, the mechanism of the intraband acceleration of electrons by the light wave field dominates. The significant changes in the optical spectrum, magnetic moment, spin polarization and electronic structure were revealed in Co2MGa and Co2MAl for different M atoms which motivate further investigations of the Co-based Heusler alloys as promising materials for spintronics. [ABSTRACT FROM AUTHOR]

The results of the optical properties study and the electronic structure calculation of ${\text{Co}}_{2}Y\text {Si}$ ($Y = \text {Ti}$ , V, Cr, Mn, Fe) Heusler alloys are presented. Temperature dependences of the electrical resistivity were studied in the temperature range from 4.2 to 300 K. Field dependences of magnetization were measured in the magnetic fields of up to 5 T. The main attention is paid to the spectral dependence of the real and imaginary parts of the dielectric constant in the wavelength range from 0.3 to $8~\mu \text{m}$ by the ellipsometric Beattie method at room temperature. Anomalous behavior of optical conductivity at infrared (IR) frequencies in Co2TiSi and Co2VSi alloys was found, which significantly differs from that in Co2MnSi, Co2FeSi, and Co2CrSi. The results obtained are discussed based on calculations of the electronic structure. Simultaneously, the correlations between the changes in these characteristics can be an indicator of the states of a half-metallic ferromagnet (HMF) or a spin gapless semiconductor (SGS). A high degree of charge carriers’ spin polarization is possible in such materials, and therefore, they are promising materials for spintronics. [ABSTRACT FROM AUTHOR]

Electronic, magnetic and elastic calculations of a new Ti2RuTl full Heusler compound have been made using the Vienna Ab-initio Simulation Package (VASP). The computations were carried out for the ferromagnetic (FM) state in the F-43 m (No.216) space group. Ground-state values of the lattice parameter, bulk modulus, volume and energy were obtained. The lattice parameter of the cubic structure was 6.478 Å. According to the electronic calculations, the spin-up electrons were found to have metallic properties while the spin-down electrons were found to have a semiconductor nature. Therefore, these metallic and semiconductor spin states showed that the Ti2RuTl full Heusler compound is a half-metallic (HM) ferromagnet with 1.00 µB/f.u. magnetic moment. Finally, the elastic calculations showed that the compound is an elastically stable, ductile material and could be a new candidate material for using in spintronics. [ABSTRACT FROM AUTHOR]

In this work, we investigate the thermoelectric properties of half-Heusler (hH) alloy NbFeTe within the framework of the semi-classical Boltzmann transport theory in integration with the density functional theory. We have evaluated the elastic properties and phonons as well. Calculations have been performed to find relaxation time for both types of carriers. Thermal conductivity is evaluated by using the Callaway model. The lattice thermal conductivity in NbFeTe (~ 3.89 W/mK at 300 K) is significantly lowered in comparison to previously studied compound NbFeSb (22.0 W/mK at 300 K) by Fang et.al. A maximum ZT equal to 0.42 and 0.86 is obtained at 1300 K in n-type and p-type NbFeTe, respectively which highlight the potential of NbFeTe hH alloy for TE applications. [ABSTRACT FROM AUTHOR]

The electronic structures of Heusler-type Fe2V1-xTaxAl and Fe2VAl1-xTax alloys were investigated by electronic band structure calculations and synchrotron radiation photoelectron spectroscopy measurements to elucidate the change in the electronic structure due to the Ta substitution. While V and Ta atoms have the same electron configuration, the hybridization between Fe 3 d and V 3 d states gradually decreases in Ta-substituted Fe2VAl alloy and the valence band is only shifted to lower binding energy side. This change of the electronic structure is hypothesized to be the underlying reason behind the improved p-type thermoelectric performance in Fe2V1-xTaxAl alloy, but the degraded n-type thermoelectric performance in Fe2VAl1-xTax alloy. Ta substitution is a promising way to further improve the thermoelectric properties of p-type Heusler-type Fe2 VAl-based alloy because of not only an increasing power factor but also decreasing thermal conductivity. [ABSTRACT FROM AUTHOR]

Electronic band structure and structural properties of two representative half-Heusler (HH) compounds with 8 electron valence count (VC), KScC and KScGe, have been studied using first principles methods within density functional theory and generalized gradient approximation. These systems differ from the well studied class of HH compounds like ZrNiSn and ZrCoSb which have VC=18 because of the absence of d electrons of the transition metal atoms Ni and Co. Electronic transport properties such as Seebeck coefficient (S), electrical conductivity (σ), electronic thermal conductivity (κe) (the latter two scaled by electronic relaxation time), and the power factor (S²σ) have been calculated using semi-classical Boltzmann transport theory within constant relaxation time approximation. Both the compounds are direct band gap semiconductors with band extrema at the X point. Their electronic structures show a mixture of heavy and light bands near the valance band maximum and highly anisotropic conduction and valence bands near the band extrema, desirable features of good thermoelectric. Optimal p- or n-type doping concentrations have been estimated based on thermopower and maximum power factors. The optimum room temperature values of S are ∼1.5 times larger than that of the best room temperature thermoelectric Bi2Te3. We also discuss the impact of the band structure on deviations from Weidemann-Franz law as one tunes the chemical potential across the band gap. [ABSTRACT FROM AUTHOR]