Phase separation and antisite defects in the thermoelectric TiNiSn half-Heusler alloys

Kirievsky, K.; Gelbstein, Yaniv; Fuks, David

doi:10.1016/j.jssc.2013.04.032

Cited by 122 publications

(77 citation statements)

References 40 publications

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“…The formation energy associated with adding Ni to the vacancy sublattice to HH ZrNiSn and HfNiSn is higher than that of adding Ni vacancies to FH ZrNi 2 Sn and HfNi 2 Sn, indicating that vacancy defects in the FH is less costly than Ni defects in HH structures. 33 The formation energies of the TiNi 1+x Sn system, in contrast, are far more symmetrical. Figure 2 also shows formation energies predicted with the cluster expansion for Ni-vacancy arrangements in larger supercells than those calculated with DFT.…”

Section: Results and Analysismentioning

confidence: 99%

Phase separation of full-Heusler nanostructures in half-Heusler thermoelectrics and vibrational properties from first-principles calculations

et al. 2015

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Abstract:Previous studies have indicated that the figure of merit (ZT) of half-Heusler (HH) alloys with composition MNiSn (M = Ti, Zr, or Hf) is greatly enhanced when the alloys contain a nano-scale full-Heusler (FH) MNi 2 Sn second phase. However, the formation mechanism of the FH nano-structures in the HH matrix and their vibrational properties are still not well understood. We report on first principles studies of thermodynamic phase equilibria in the MNiSn-MNi 2 Sn pseudo-binary system as well as HH and FH vibrational properties. Thermodynamic phase diagrams as functions of temperature and Ni concentration were developed using density functional theory (DFT) combined with a cluster expansion and Monte Carlo simulations. The phase diagrams show very low excess Ni solubility in HH even at high temperatures, which indicates that any Ni excess will decompose into a two-phase mixture of HH and FH. Vibrational properties of HH and FH alloys are compared. Imaginary vibrational modes in the calculated phonon dispersion diagram of TiNi 2 Sn indicate a dynamical instability with respect to cubic [001] transverse acoustic modulations. Displacing atoms along unstable vibrational modes in cubic TiNi 2 Sn reveal lower energy structures with monoclinic symmetry. The energy of the monoclinic structures are found to depend strongly on the lattice parameter. The origin of the instability in cubic TiNi 2 Sn and its absence in cubic ZrNi 2 Sn and HfNi 2 Sn is attributed to the small size of the Ti 3d shells compared to Zr and Hf atoms. Lattice constants and heat capacities calculated by DFT agree well with experiment.

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Section: Results and Analysismentioning

confidence: 99%

Phase separation of full-Heusler nanostructures in half-Heusler thermoelectrics and vibrational properties from first-principles calculations

et al. 2015

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“…Several classes of thermoelectric materials, such as skutterudite [5,6], tellurides [7][8][9][10], half-Heuslers [11,12], and silicides [13,14], have been modified to reach high ZT value. Recently, ternary diamond-like semiconductor of Cu 2 SnSe 3 has emerged as a new potential thermoelectric material due to its relatively high carrier mobility and quite low thermal conductivity.…”

Section: Introductionmentioning

confidence: 99%

Enhanced Thermoelectric Properties of Graphene/Cu2SnSe3 Composites

Zhao

Wang

2017

Crystals

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Cu 2 SnSe 3 material is regarded as a potential thermoelectric material due to its relatively high carrier mobility and low thermal conductivity. In this study, graphene was introduced into the Cu 2 SnSe 3 powder by ball milling, and the bulk graphene/Cu 2 SnSe 3 thermoelectric composites were prepared by spark plasma sintering. The graphene nanosheets distributed uniformly in the Cu 2 SnSe 3 matrix. Meanwhile, some graphene nanosheets tended to form thick aggregations, and the average length of these aggregations was about 3 µm. With the fraction of graphene increasing, the electrical conductivity of graphene/Cu 2 SnSe 3 samples increased greatly while the Seebeck coefficient was decreased. The introduction of graphene nanosheets can reduce the thermal conductivity effectively resulting from the phonon scattering by the graphene interface. When the content of graphene exceeds a certain value, the thermal conductivity of graphene/Cu 2 SnSe 3 composites starts to increase. The achieved highest figure of merit (ZT) for 0.25 vol % graphene/Cu 2 SnSe 3 composite was 0.44 at 700 K.

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“…10 Concerning bulk oxidation, threshold temperatures have been determined, above which MgO (723 K), SiO 2 (1000 K) and Mg 2 SiO 4 (1270 K) can form within bulk Mg 2 Si. 4,5 Production techniques for Mg 2 Si are numerous, among them spark plasma sintering (SPS) 11 or fieldactivated and press-assisted sintering (FAPAS). 12,13 In this study, bulk Mg 2 Si-based TE materials are produced through hot extrusion.…”

Section: Introductionmentioning

confidence: 99%

Hot Extruded Polycrystalline Mg2Si with Embedded XS2 Nano-particles (X: Mo, W)

Bercegol

Christophe

Keshavarz

et al. 2016

Journal of Elec Materi

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Due to their abundant, inexpensive and non-toxic constituent elements, magnesium silicide and related alloys are attractive for large-scale thermoelectric (TE) applications in the 500-800 K temperature range, in particular for energy conversion. In this work, we propose a hot extrusion method favorable for large-scale production, where the starting materials (Mg 2 Si and XS 2 , X: W, Mo) are milled together in a sealed vial. The MoS 2 nano-particles (0.5-2 at.%) act as solid lubricant during the extrusion process, thus facilitating material densification, as confirmed by density measurements based on Archimedes' method. Scanning electron microscopy images of bulk extruded specimens show a wide distribution of grain size, covering the range from 0.1 lm to 10 lm, and energy dispersive spectroscopy shows oxygen preferentially distributed at the grain boundaries. X-ray diffraction analysis shows that the major phase is the expected cubic structure of Mg 2 Si. The TE properties of these extruded alloys have been measured by the Harman method between 300 K and 700 K. Resistivity values at 700 K vary between 370 lX m and 530 lX m. The ZT value reaches a maximum of 0.26 for a sample with 2 at.% MoS 2 . Heat conductivity is reduced for extruded samples containing MoS 2 , which most likely behave as scattering centers for phonons. The reason why the WS 2 particles do not bring any enhancement, for either densification or heat transfer reduction, might be linked to their tendency to agglomerate. These results open the way for further investigation to optimize the processing parameters for this family of TE alloys.

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Phase separation and antisite defects in the thermoelectric TiNiSn half-Heusler alloys

Cited by 122 publications

References 40 publications

Phase separation of full-Heusler nanostructures in half-Heusler thermoelectrics and vibrational properties from first-principles calculations

Phase separation of full-Heusler nanostructures in half-Heusler thermoelectrics and vibrational properties from first-principles calculations

Enhanced Thermoelectric Properties of Graphene/Cu2SnSe3 Composites

Hot Extruded Polycrystalline Mg2Si with Embedded XS2 Nano-particles (X: Mo, W)

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