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Theoretical and experimental results exploring a half‐Heusler compound TmPdSb with unusual band order and metallic surface states are presented. Typically, the half‐Heusler systems exhibit topological features in a semimetallic state, and trivial ones in an insulating state. Topological properties of the most of half‐Heusler systems are related to the band inversion around the Fermi level, similar to this observed in CdTe/HgTe systems. In the case of TmPdSb, the gapped electronic band structure with “band inversion” in the conductance band is observed, while the slab‐like system realized metallic surface states. The bulk insulating nature of the compound is corroborated by means of electrical transport measurements. The experimental data reveal several features due to the presence of metallic surface states, such as linear magnetoresistance and weak‐antilocalization effect, characterized by enhanced coherence length and a very large number of surface conductive channels. The findings reveal new features of the rare‐earth bearing half‐Heusler. [ABSTRACT FROM AUTHOR]

In this study, we have predicted the ground-state properties of the half-Heusler RuCrSb compound using the plane-wave pseudopotential method. The structural optimization signifies that the material is energetically favoured in the ferrimagnetic state in α-phase with optimized lattice parameter 6.025 Å. The positive cohesive energy as well as elastic constants indicate that the compound is thermodynamically and mechanically stable. The absence of a negative phonon dispersion curve also confirms that the sample material is dynamically durable. In order to explore the nature of bonding forces and determine the mechanical strength of the system, the elastic properties have been computed. Moreover, using the quasi-harmonic Debye model, it has been possible to determine the thermodynamical properties with regard to temperature for various pressures. For the strongly correlated d-transition electrons of the studied compound, we incorporated on-site Coulomb repulsion term (U) on GGA scheme during electronic and magnetic calculations. The studied compound reveals half-metallic performance, i.e., it conveys 100% spin polarization at the Fermi energy level ( E F ) under both GGA and GGA + U approximations. The total magnetic moments ( M t ) of the sample material is 1 μ B , which is in good agreement with the 18 Slater-Pauling rule; i.e., M t = Z t – 18. The magnetism source is predominantly from the Cr atom in the studied compound. Moreover, the electronic properties are also supported by the fermi surface, charge density distribution and the Bader charge method. As the Curie temperature ( T C ) of the studied material is observed to be higher than room temperature; the material is suitable for spintronic applications. [ABSTRACT FROM AUTHOR]

Research shows that the thermoelectric properties of topologically nontrivial semimetallic half-Heulser compounds can be optimized by topological phase transitions. Using density functional theory, we have found that the topologically semimetallic HfIrBi compound can be converted into semiconductors under hydrostatic pressures. We further investigate the band structures, phonon dispersions, and thermoelectric properties of the p-type HfIrBi compound under different hydrostatic pressures. The maximum ZT value of the p-type HfIrBi compound under 25 GPa pressure at 1000 K can reach 1.43, which is approximately 2.46 times larger than that without hydrostatic pressure. Therefore, the topological phase transitions induced by hydrostatic pressures point to the synthesis of new thermoelectric materials. [ABSTRACT FROM AUTHOR]

We thoroughly investigated the electronic structure and various properties of the half-Heusler compound ScRhTe using density functional theory calculations. The electronic structure shows that ScRhTe is a narrow-band-gap semiconductor. Owing to its characteristic conduction-band structure, ScRhTe has a higher Seebeck coefficient and a higher power factor for n-type doping than for p-type doping, with the maximum value of −493 µV K−1 appearing at 900 K. The optimal carrier concentration is approximately 5 × 1019 cm−3–1 × 1020 cm−3. In addition, ZTe is estimated as 0.95 at a doping level of approximately 1019 cm−3. Under pressure, the band structure changes from a direct to an indirect band gap, and the band gap increases as the pressure changes from tensile to compressive. The thermoelectric properties of ScRhTe improve under compressive pressure, whereas the optical properties improve greatly under tensile pressure. By varying the pressure, the electronic structure and various properties of ScRhTe can be effectively adjusted, which signifies that ScRhTe has the potential to become an important optoelectronic or thermoelectric material. [ABSTRACT FROM AUTHOR]

The mechanical, dynamical and thermodynamical properties of the RuMnAs compound have been explored using the first-principle calculations under hydrostatic pressure. The sample material is stable in the FCC cubic phase verified by the elastic constants and positive cohesive energy up to a pressure of 15 GPa. The positive phonon frequency further strengthened the dynamical stability of the material in the cubic phase. The lattice constant of the system decreases linearly with the influence of pressure. The independent elastic constants ( C 11 and C 12 ), hardness of the material, ionic bonding and the ductility of the system increase almost linearly due to applied pressure. The thermodynamics study reflects that pressure has a negative effect on heat capacity, coefficient of thermal expansion and Gruneisen parameter in the examined compound, although Debye temperature increases with increased pressure. [ABSTRACT FROM AUTHOR]

Electron spin resonance (ESR) of diluted Nd(3+) ions in the topologically nontrivial semimetallic (TNSM) YBiPt compound is reported. The cubic YBiPt compound is a non-centrosymmetric half Heusler material which crystallizes in the F43m space group. The low temperature Nd(3+) ESR spectra showed a g-value of 2.66(4) corresponding to a Γ6 cubic crystal field Kramers' doublet ground state. Remarkably, the observed metallic and diffusive (Dysonian) Nd(3+) lineshape presented an unusual dependence with grain size, microwave power, Nd(3+) concentration and temperature. Moreover, the spin dynamic of the localized Nd(3+) ions in YBiPt was found to be characteristic of a phonon-bottleneck regime. It is claimed that, in this regime for YBiPt, phonons are responsible for mediating the diffusion of the microwave energy absorbed at resonance by the Nd(3+) ions to the thermal bath throughout the skin depth (δ ≃ μm). We argue that this is only possible because of the existence of highly mobile conduction electrons inside the skin depth of YBiPt that are strongly coupled to the phonons by spin-orbit coupling. Therefore, our unexpected ESR results point to a coexistence of metallic and insulating behaviors within the skin depth of YBiPt. This scenario is discussed in the light of the TNSM properties of this compound.

N-type half-Heusler NbCoSn is a promising thermoelectric material due to favourable electronic properties. It has attracted much attention for thermoelectric applications while the desired p-type NbCoSn counterpart shows poor thermoelectric performance. In this work, p-type NbCoSn has been obtained using Sc substitution at the Nb site, and their thermoelectric properties were investigated. Of all samples, Nb0.95Sc0.05CoSn compound shows a maximum power factor of 0.54 mW/mK2 which is the highest among the previously reported values of p-type NbCoSn. With the suppression of thermal conductivity, p-type Nb0.95Sc0.05CoSn compound shows the highest measured figure of merit ZT = 0.13 at 879 K.

We thoroughly investigated the electronic structure and various properties of the half-Heusler compound ScRhTe using density functional theory calculations. The electronic structure shows that ScRhTe is a narrow-band-gap semiconductor. Owing to its characteristic conduction-band structure, ScRhTe has a higher Seebeck coefficient and a higher power factor for n-type doping than for p-type doping, with the maximum value of −493 µV K−1 appearing at 900 K. The optimal carrier concentration is approximately 5 × 1019 cm−3–1 × 1020 cm−3. In addition, ZTe is estimated as 0.95 at a doping level of approximately 1019 cm−3. Under pressure, the band structure changes from a direct to an indirect band gap, and the band gap increases as the pressure changes from tensile to compressive. The thermoelectric properties of ScRhTe improve under compressive pressure, whereas the optical properties improve greatly under tensile pressure. By varying the pressure, the electronic structure and various properties of ScRhTe can be effectively adjusted, which signifies that ScRhTe has the potential to become an important optoelectronic or thermoelectric material.

N-type half-Heusler NbCoSn is a promising thermoelectric material due to favourable electronic properties. It has attracted much attention for thermoelectric applications while the desired p-type NbCoSn counterpart shows poor thermoelectric performance. In this work, p-type NbCoSn has been obtained using Sc substitution at the Nb site, and their thermoelectric properties were investigated. Of all samples, Nb0.95Sc0.05CoSn compound shows a maximum power factor of 0.54 mW/mK2 which is the highest among the previously reported values of p-type NbCoSn. With the suppression of thermal conductivity, p-type Nb0.95Sc0.05CoSn compound shows the highest measured figure of merit ZT = 0.13 at 879 K. [ABSTRACT FROM AUTHOR]

Structural, electronic, elastic, and transport properties of FeVX (X = As, P) half-Heusler (HH) compounds have been calculated using density functional theory (DFT). The generalized gradient approximation developed by Perdew–Burke–Ernzerhof (GGA-PBE) is utilized for the calculation of the structural properties and the mechanical parameters of FeVX (X = As, P), indicating that the studied compounds are mechanically stable. The Tran and Blaha-modified Becke–Johnson potential (TB-mBJ) is utilized to improve the investigation of the electronic structure and also indicates that the FeVX (X = As, P) compounds are narrow-gap semiconductors. Calculations of transport efficiency are performed using the semiclassical Boltzmann theory. The figure of merit ZT is near unity at room temperature, indicating that both compounds are good candidates for use in transport devices. [ABSTRACT FROM AUTHOR]

Based on first-principles simulation and semi-classical Boltzmann transport theory, we investigated the electronic structures and optical and thermoelectric properties of ternary half-Heusler compound TaCoSn. Results indicated that TaCoSn is a narrow-gap semiconductor. The accidental degeneracy of the valence-band maximum resulted in higher p-type Seebeck coefficients than n-type doping, in which the highest value reached 660  μ V/K at 900 K. The optimum carrier concentration is approximately 10 19  cm −3 . In comparison to the experimental results of TaCoSn, we obtained the electrical conductivity and power factor of TaCoSn as a function of temperature and carrier concentrations, respectively. TaCoSn exhibits a large power factor of 10.93  μ W c m − 1 K − 2  at 820 K. The calculated electrical conductivity and optical absorption coefficient agree well with the reported experimental data. Z T e shows a relatively high value for carrier concentrations at approximately 10 19  cm −3 , and the p-type is superior to the n-type. These results indicate that TaCoSn can be used as an important photoelectric and thermoelectric material in the future. [ABSTRACT FROM AUTHOR]

The structural, electronic, elastic, and thermoelectric properties of TiIrX (X = As and Sb) half-Heusler compounds with 18 valence electrons were studied using density functional theory. The generalized gradient approximation of Perdew-Burke and Ernzerhof used for calculation of the structural parameters and elastic properties of TiIrAs and TiIrSb denotes that the computed lattice constants were in excellent agreement with the available experimental data and previous theoretical works. Furthermore, the calculated elastic constants for both compounds satisfy the Born criteria indicating their mechanical stabilities. The modified Becke-Johnson potential (TB-mBJ) was used to provide a better description of the electronic structures, which indicate that both compounds are narrow-gap semiconductors. Additionally, the investigations of thermoelectric performance were carried out using the results of ab initio band-structure calculations and the semi-classical Boltzmann theory within the constant relaxation time approximations. The predicted values of the figure of merit ZT are close to unity at room temperature. This reveals that TiIrAs and TiIrSb compounds are excellent candidates for practical applications in the thermoelectric devices. [ABSTRACT FROM AUTHOR]

We first investigate the structural, electronic and magnetic properties of half-Heusler compounds LiXGe (X = Ca, Sr and Ba), by using the first-principles calculations within full-potential local-orbital minimum-basis method. The calculations show that all compounds are half-metallic ferromagnets with the same magnetic moment of 1.00 μ B per formula unit and all compounds follow the Slater-Pauling rule: M t o t = ( 8 − Z t o t ) μ B . In the aspects of phonon dispersion, cohesive energy and formation energy, we found all the compounds are found to be stable. Our calculations also show that the half-metallicities can be preserved with lattice constants from −3.6% to 21.4%, −3.8% to 16.1% and −1.2% to 14.7% for LiCaGe, LiSrGe and LiBaGe. At the end the elastic properties for the all three compounds are also reported. [ABSTRACT FROM AUTHOR]

A model of LiMgZn X half-Heusler compounds with the chalcopyrite structure is considered. The electronic structure is studied from first principles, showing that LiMgZn X are direct-gap crystals, except for pseudo-direct-gap LiMgZnP, with a band gap of 2.7 eV, 2.2 eV, 3.3 eV, and 2.5 eV for X = N, P, As, and Sb, respectively. The band structure and chemical bonding in the model crystals are found to be similar to those in LiMg X and LiZn X half-Heusler crystals. Total electron density and deformation electron density distributions are obtained. It is found that Mg- X and Zn- X ionic-covalent bonds are stronger than Li- X ionic bonds in LiMgZn X crystals, which allows Li atoms to move in the space between Mg X and Zn X cation tetrahedra. [ABSTRACT FROM AUTHOR]

The electronic structure and thermoelectric properties of half-Heusler A B Pb ( A = Hf, Zr; B = Ni, Pd) compounds were investigated by the first-principles calculation. Our results indicate all the four compounds are narrow-gap semiconductors. The value of power factor over relaxation time ( S 2 σ / τ ) first increases and then decreases with carrier concentration increasing, because of the narrower band gap. The optimal p- or n-type doping concentrations with different temperature have been estimated. Comparing with the experimental data of ZrNiPb, we get the thermopower S , power factor S 2 σ and the maximum power factor as a function of carrier concentration and temperature. Our calculated power factors are in good agreement with the experimental data, and give some suggestions to improve the thermoelectric properties. [ABSTRACT FROM AUTHOR]

The Ni-doped ZrCo1−xNixSb half-Heusler compounds were prepared by arc-melting and spark plasma sintering technology. X-ray diffraction analysis results showed that all samples were crystallized in a half-Heusler phase. Thermoelectric properties of ZrCo1−xNixSb compounds were measured from room temperature to 850 K. The electrical conductivity and the absolute value of Seebeck coefficient increased with the Ni-doping content increasing due to the Ni substitution at Co. sites. The lattice thermal conductivity of ZrCo1−xNixSb samples was depressed dramatically because of the acoustic phonon scattering and point defect scattering. The figure of merit of ZrCo1−xNixSb compounds was improved due to the decreased thermal conductivity and improved power factor. The maximum ZT value of 0.24 was achieved for ZrCo0.92Ni0.08Sb sample at 850 K.

We performed first-principles-based calculations of density of states, electrical conductivity, Seebeck coefficient, and thermal conductivity of a p-type half-Heusler compounds (ZrCoSb) to identify the alloy composition that gives rise to a high thermoelectric figure-of-merit. The strategy here is to substitute constituent atoms of ZrCoSb with lighter or heavier homologous element to reduce thermal conductivity without appreciably altering electrical properties. The density-of-states calculations reveal that substitution of Sb does not singnificantly alter the electronic states near Fermi level. The small influence on electrical properties was also confirmed by performing calculations for ZrCoBi, where the power factor is slightly larger than that of ZrCoSb. The effect of alloying on thermal conductivity reduction was quantified by equilibrium molecular dynamics simulations of ZrCoSb1-xBix with force fields obtained from first principles. With increasing alloy fraction x, thermal conductivity rapidly reduces to less than 15% of that of ZrCoSb and nearly saturates above x～20%, suggesting ZrCoSb0.8Bi0.2 to be a reasonable alloy composition for high thermoelectric performance.

We investigate the band structure, magnetism and density of states of half-Heusler compounds based on the first-principle calculations. Combined with molecular orbital hybridization theory, we discuss the influence of the main-group element on half-metallic properties of . It is found that the replacement of Ge for Si in CoCrSi can adjust the position of the Fermi level, and while it has no impact on the energy gap width and magnetic structure. However, the substitution of P for Si can effectively adjust the magnetism without disrupting its half-metallicity. Our results demonstrate that the electronic structure of is mainly dependent on the number of valence electrons of the main-group element. [ABSTRACT FROM AUTHOR]

The standard enthalpies of formation of selected ternary half-Heusler type compositions XYZ (X = Au, Co, Fe, Ir, Ni, Pd, Pt, Rh, Ru; Y = Hf, Mn, Ti, Zr; Z = Ga, Sn) were measured using high temperature direct reaction calorimetry. The measured standard enthalpies of formation (in kJ/mole of atoms) of the half-Heusler compounds (prototype MgAgAs, Pearson symbol cF12, space group F-43m) are, IrMnSn (−29.4 ± 1.8); NiTiSn (−52.6 ± 2.4); PtHfSn (−98.8 ± 3.4); PtMnSn (−55.8 ± 2.6); PtTiSn (−93.6 ± 3.3); PtZrSn (−104.9 ± 3.8); for the B2 compound (prototype CsCl, Pearson symbol cP2, space group Pm-3m), RuMnGa (−26.9 ± 1.7); for the C1 structured (prototype CaF 2 , Pearson symbol cF12, space group Pm-3m) or the C1 b structured compound IrMnGa (−40.9 ± 1.7). Indicative standard enthalpies of formation of the following compounds were obtained, half-Heusler compounds AuMnSn, CoTiSn, IrZrSn, NiHfSn, NiZrSn, PdHfSn, PdZrSn, RhTiSn; Heusler compound (prototype Cu 2 MnAl, Pearson symbol cF16, space group Fm-3m) RhMnSn; hexagonal compound (prototype BeZrSi, Pearson symbol hP6, space group P6 3 /mmc) PtMnGa and another type of hexagonal compound (prototype RhHfSn, Pearson symbol hP18, space group P-62c) RhHfSn, IrZrsn, RhZrSn. Values were compared with ab initio calculations from AFLOW and OQMD. Lattice parameters of these compounds were determined using X-ray diffraction (XRD) analysis. Microstructures were characterized using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Selected alloys were further annealed to investigate phase transformations and phase relationships. [ABSTRACT FROM AUTHOR]

Total, difference, and deformation electron densities are calculated from the first principles using the density functional theory and the sublattice method for LiBX (B = Mg, Ca, Zn; X = N, P, As) crystals with the sphalerite structure. The nature and formation features of the chemical bonding caused by a change in the chemical composition are revealed. A weak bond between Li ions with X anions enables their displacements in the space between crystal-forming tetrahedral (BX) groups. It is found that Ca-X bonds are mainly ionic and in a series of crystals the ionic covalent Li-B bond is traced. [ABSTRACT FROM AUTHOR]

We report various phase transitions in half-Heusler TbPtBi compound using density functional theory. Specifically, the inclusion of spin-orbit coupling (SOC) leads to the band inversion resulting in the transition from the metallic to the topological semimetallic phase. However, in the presence of SOC, there is a phase transition from the topological semimetal to the trivial semimetal when the material is subjected to compressive strain-7%. Subsequently, under the further increase of compressive strain(⩾​​-7%), we find an opening of a direct band gap at the point, driving the system from the trivial semimetallic to a semiconducting state with changes in the sequence of the bands. In the absence of SOC, only the transition from the metallic to the semiconducting phase is noticed. Under tensile strain, the TbPtBi compound maintains its phase as in the unstrained condition but with an increase in the hole pocket at the Fermi level, both in the absence and presence of SOC. These tunable phase transitions (especially as a fraction of strain) make this compound very promising for application in various quantum devices, such as highly sensitive strain gauges., (© 2022 IOP Publishing Ltd.)

Ti 0.75 NiSb is a half-Heusler compound with low lattice thermal conductivity due to a large number of cation vacancies. However, the higher carrier concentration limits the improvement of its thermoelectric performance. In this paper, magnetic Fe nanoparticles with a size of 30 nm are composited into Ti 0.75 NiSb in the form of the second phase. The charge transfer between Fe nanoparticles and Ti 0.75 NiSb leads to a decrease in carrier concentration. The strong interaction between the magnetic moment and carriers enhances the electron scattering, so that the scattering factor increases and the mobility decreases. The combined effect results in an increase of about 10% in the Seebeck coefficient and a decrease by about 14% in the electronic thermal conductivity at 873 K for the composite Ti 0.75 NiSb+2 mol % Fe. Meanwhile, the magnetic Fe nanoparticles provide additional scattering centers, leading to a decrease in lattice thermal conductivity. As a result, a zT value of 0.4 at 873 K is achieved for the composite Ti 0.75 NiSb+2 mol % Fe, which is 21% higher than that of Ti 0.75 NiSb. This work demonstrates that the compositing magnetic nanoparticles Fe can enhance the thermoelectric performance of Ti 0.75 NiSb.

Abstract: The band topology of a new half-Heusler family with 8 valence electrons composed of light elements is investigated by the first-principle calculations. Many of these compounds are predicted to be topological insulators. The new topological insulators exhibit great band inversion strength (up to ). Both the occurrence of the band inversion and the opening topological insulating gap can be performed only by the strain engineering. Based on these results, we also argue that the spin–orbit coupling effect is not an essential factor in the band inversion and the formation of topological insulating gap. [Copyright &y& Elsevier]

Abstract: A density functional theory was used to study the origin of ferromagnetism in the half-Heusler XRbCs compounds (where X=N, P, and As). The results predict a stable atomic arrangement with a ferromagnetic order. The spin-polarized calculations give a total magnetic moment of about . The most important property in these hypothetical compounds is that the half-metallicity is originated from the polarization of the p-orbitals originated from N, P, and As atoms. We also find that the half-metallicity is maintained on a wide range of lattice constants and therefore offers the possibility to grow such materials on various semiconductor substrates. [Copyright &y& Elsevier]

• The thermoelectric properties are investigated by the first principle calculation. • Zr doped compounds possess strong phonon-phonon scattering. • Zr substitution hardly reduces the power factors. • Hf 0.75 Zr 0.25 CoBi and Hf 0.25 Zr 0.75 CoBi possess ZT of 2.74 and 2.59 at 1200 K. Based on the first-principle calculation and semi-classical Boltzmann transport theory, the electronic structures and thermoelectric properties of Hf 1− x Zr x CoBi (x = 0 , 0.25 , 0.5 , 0.75 , 1) compounds have been systematically investigated. These compounds possess narrow bandgaps and they are thermodynamically stable. The low frequency optical branches couple with the acoustic modes in the Zr doped compounds, which highly enhance the phonon scattering. The Zr substitutions hardly reduce the power factors when x = 0.25 and 0.75, but substantially reduce the thermal conductivity and thus, improve the figure of merit. The predicted ZT of p-type Hf 0.75 Zr 0.25 CoBi and Hf 0.25 Zr 0.75 CoBi can reach up to 2.74 and 2.59 at 1200 K, which is much larger than that of the pure HfCoBi compound. This work implies that Hf 0.75 Zr 0.25 CoBi and Hf 0.25 Zr 0.75 CoBi are promising high-efficiency thermoelectric materials. [ABSTRACT FROM AUTHOR]

Abstract: The electronic structure and optical properties of TiCoSb are studied by the first-principles calculation. It is found that the band gaps increase with the pressure increasing. It is noted that the increase of the band gap is due to the electrons of Ti 3d and Co 3d of the valence band (VB) shifting away from the Fermi level. Our calculation indicates that TiCoSb has the large density of state near the Fermi level; moreover, the changes of the density of states near the Fermi level mainly are caused by Ti 3d and Co 3d under the different pressures. It is noted that the absorption edge increases with an increase of pressure. As pressure increases, the static dielectric constants ε 1(0) decrease. All peaks of the imaginary part of the dielectric function ε 2(ω) move towards higher energies within increasing pressure. [Copyright &y& Elsevier]

We report an ab initio study of vibrational and thermodynamic properties of TiNiSn, a half-Heusler alloy that has been investigated in the context of thermoelectrics, based on density functional theory and density functional perturbation theory. The quasiharmonic approximation, where the Helmholtz free energy obtained from phonons of multiple strained structures is fitted to a model equation of state, is employed to estimate thermodynamic properties. Good quantitative correspondence is achieved between experimental observations and our theoretical calculation for various thermodynamic quantities: lattice parameter, thermal expansion coefficient, and heat capacity. Estimates of lattice thermal conductivity are also provided by using a semianalytic model previously proposed in the literature. Though this yields good qualitative agreement, a more accurate ab initio approach that explicitly includes anharmonic interactions between atoms should be employed for quantitative predictions of thermal conductivity. [ABSTRACT FROM AUTHOR]

Abstract: We report an induction-melting spark-plasma-sintering synthesis process of the nanocomposite material composed of (TiZrHf)(CoNi)Sb coarse grains and in situ formed InSb nanoinclusions that occur primarily on the grain boundaries. We were able to qualitatively control the amount of InSb nanoinclusions by varying the In and Sb contents in the starting materials. The effects of the nanoinclusion formation and the matrix–nanoinclusion boundaries on the thermoelectric properties have been studied and correlated. In particular, the nanoinclusion-induced electron injection and electron filtering mechanisms helped to simultaneously decrease the resistivity, enhance the Seebeck coefficient and reduce the thermal conductivity of the nanocomposite. A figure of merit of ZT ∼0.5 was attained at 820K for the sample containing 1at.% InSb nanoinclusions, which is a 160% improvement over the sample containing no nanoinclusions. The experimental results are discussed in the context of the effective medium model formerly proposed by Bergman and Fel. [Copyright &y& Elsevier]

Abstract: Fe-doped NiZrSn polycrystalline ingots were prepared using arc melting method. Microstructure and electrical properties of the ingots were investigated. According to the EDX results, the solubility of Fe in the C1b phase of the NiZrSn is about 2% by arc melting method. The electrical resistivity of low Fe-doped NiZrSn shows semiconducting temperature dependence and the transport gap estimated from activation plot is about 80meV. [Copyright &y& Elsevier]

Abstract: Half-Heusler compounds: MNiSn (M=Ti, Zr, Hf) are considered as a candidate of environmentally friendly and low-cost thermoelectric (TE) materials. Although the thermomechanical properties are quite important when utilizing the half-Heusler compounds in TE devices, such properties have been scarcely reported. In the present study, we tried to collect the data of the thermal expansion coefficient and the melting temperature (T m) of MNiSn. The thermal expansion coefficient was evaluated by means of two methods: the dilatometer measurement and the high temperature X-ray diffraction analysis. The T m was evaluated from the differential thermal analysis. The relationship between the thermal expansion coefficient and the T m of the half-Heusler compounds was studied. [Copyright &y& Elsevier]

Abstract: Nearly single-phased TiNiSn half-Heusler compound thermoelectric materials were synthesized by combining mechanical alloying (MA) and spark plasma sintering (SPS) in order to reduce its thermal conductivity by refining the grain sizes. Although TiNiSn compound powders were not synthesized directly via MA, dense bulk samples of TiNiSn compound were obtained by the subsequent SPS treatment. It was found that an excessive Ti addition relative to the TiNiSn stoichiometry is effective in increasing the phase purity of TiNiSn half-Heusler phase in the bulk samples, by compensating for the Ti loss caused by the oxidation of Ti powders and MA processing. The maximum power factor value obtained in the Ti-compensated sample is 1720μWm−1 K−2 at 685K. A relatively high ZT value of 0.32 is achieved at 785K for the present undoped TiNiSn compound polycrystals. [Copyright &y& Elsevier]

Abstract: Ge-doped TiCoSb-based half-Heusler compounds, TiCoGe x Sb1−x (x =0–0.2), were prepared by arc melting and spark plasma sintering (SPS). The electrical conductivity, Seebeck coefficient and thermal conductivity were measured from room temperature to 850K. The Seebeck coefficient changed from negative to positive by Ge doping, and the electrical conductivity increased with increasing Ge content. The lattice thermal conductivity for TiCoGe x Sb1−x is considerably reduced, because the point defects induced by Ge substitution for Sb intensively scatter the thermal phonons. The mass fluctuation part Γ mass and strain field fluctuation part Γ stra were estimated, and it was found that the reduction of lattice thermal conductivity is mainly attributed to the strain field fluctuation. Ge doping improved the thermoelectric figure of merit ZT of TiCoSb and the maximum ZT value of 0.16 was obtained for TiCoGe0.15Sb0.85 sample at 850K. [Copyright &y& Elsevier]

Abstract: Half-Heusler compounds of Sn-doped TiCoSb “TiCoSn x Sb1−x (x =0.0, 0.01, and 0.05)” were prepared and their thermoelectric properties were measured above room temperature. From the EDX analysis, all the samples have three phases: the TiCoSn x Sb1−x , Co-rich, and Ti-rich phases. The values of the thermoelectric power increase with Sn doping, and a positive thermoelectric power is obtained in the sample of TiCoSn0.05Sb0.95. The thermal conductivity decreases both with increasing temperature and with Sn content. The maximum value of ZT for p-type material is 0.030 at 988K in the sample of TiCoSn0.05Sb0.95. [Copyright &y& Elsevier]

Abstract: The half-Heusler compound TiCoSb was prepared by arc melting. We annealed the ingot for 1, 3, and 7 days at 1173K, and measured the electrical resistivity, thermoelectric power, and thermal diffusivity in the temperature region from 350 to 973K. We found that the dimensionless figure of merit ZT decreased with increasing annealing period. We have considered that the changes of thermoelectric properties are derived from two competitive phenomena; the first one is the introduction of structural disorder due to evaporation of impurity antimony, and the second one is the improvement of the disorder effect by annealing. [Copyright &y& Elsevier]

Half-Heusler compounds have distinguished themselves as outstanding thermoelectric materials on account of high temperature stability and large thermopower. However, the dimensionless figure of merit of traditional half-Heusler alloys remains low. In this study, we investigate the thermoelectric performance of novel Zr X Pb ( X = Ni, Pd, and Pt) ternary compounds by semi-classical Boltzmann transport theory combining with deformation potential. The n-type ZrNiPb and ZrPtPb exhibits obviously large ZT values of 1.71 around 650 K and 1.75 around 1200 K, with 1.17 × 10 20  cm -3 and 3.43 × 10 20  cm -3 , respectively. The electron and phonon structure calculations demonstrate that for the n-type Zr X Pb ( X = Ni, Pd, and Pt) compounds, doping at Pb site can not only modify the carrier concentrations but also significantly decrease the lattice thermal conductivity. These investigations are expected to be beneficial to the exploration of novel high ZT thermoelectric materials., (© 2021 IOP Publishing Ltd.)

Tailoring nanostructures is nowadays a common approach for enhancing the performance of thermoelectric Heusler compounds by decreasing the thermal conductivity without significantly affecting the electrical conductivity. However, the most widely reported method for obtaining nanostructured thermoelectrics, an approach based on crushing as-cast alloy ingots followed by sintering of the debris, only gives limited control of the final nanostructure due to residual elemental segregation after casting. Here, a novel approach for fabricating nanostructured Heusler compounds is presented, which is based on crystallizing an amorphous precursor of NbCo 1.1 Sn composition. This method yields two distinct nanostructures, namely one comprising only half-Heusler grains and another one comprising half-Heusler grains and full-Heusler nano-precipitates. The latter sample exhibits enhanced negative Seebeck coefficients as compared to the former over a wide temperature range. Using advanced characterization techniques, such as high-resolution transmission electron microscopy and atom probe tomography, in conjunction with ab initio density functional theory, detailed insights into the nanostructure and electrical properties of the specimens are provided. Filtering of low energy and mobility electrons at the half-Heusler and full-Heusler interface along with the formation of Co interstitial defects in the half-Heusler matrix are proposed to be the possible causes for the enhanced Seebeck coefficient of the nano-precipitate containing specimen. ga1 • We propose a novel approach for fabricating nanostructured Heusler compounds, based on crystallizing an amorphous precursor. • We performed nano-scale characterization of the prevailing half- and full-Heusler phases in the crystallized specimens. • Formation of half-Heusler nano-precipitates was found to enhance the Seebeck coefficient. • Filtering of low energy electrons at interfaces and formation of Co interstitials in the half-Heusler matrix enhanced the Seebeck coeffcient. [ABSTRACT FROM AUTHOR]

Abstract: Electrical resistivity, structural and magnetic properties of polycrystalline samples of a half-Heusler alloy, CoTiSb, and the effect of the substitution of V for Ti on these properties in have been investigated. The temperature dependence of the electrical resistivity in CoTiSb above 10K is found to exhibit, on the whole, semiconducting behavior, which agrees with previous results. For samples in which V is substituted for Ti with the structure is found to be the half-Heusler type as with . As V increases from to 0.05, the magnitude of the resistivity increases, but the temperature dependence is similar to that of . For the sample with , however, the magnitude of the resistivity suddenly decreases to the value smaller than that of , and the slope of the temperature dependence of the resistivity becomes positive down to 25K. [Copyright &y& Elsevier]