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Higher manganese silicides (denoted as MnSiγ ) are a prominent class of intermetallic compound for thermoelectric applications that crystallizes into a Nowotny Chimney Ladder (NCL) phase and constitutes a higher concentration of silicon with odd stoichiometry, typically represented by an irrational number. In this work, the genesis of Si odd stoichiometry and secondary phase relations in silicon-rich and silicon-deficient MnSix is presented to clarify the significance of labile (i.e., easily alterable) Si-subsystem in inheriting the modulated lattice structure with characteristic anharmonicity. The transport properties show an interrelation to the presence of a secondary phase, which is driven by the odd stoichiometry, where the thermoelectric figure of merit (zT) is found to be optimal for MnSi1.74. The structural characterization of rapidly solidified melt-spun ribbons and spark plasma sintered bulk specimens reveal a characteristic presence of MnSi and Si as secondary phases in Si-deficient (x ≈ 1.5) and Si-excess (x ≈ 2) compositions of nominal MnSix, respectively, that coexists with the major MnSiγ based NCL phase. This study provides the fundamental basis of phase evolution and the relevance of odd stoichiometry in silicon-rich manganese silicides which exhibit fascinating phonon dynamics in optimal MnSi1.74 stoichiometry. [ABSTRACT FROM AUTHOR]

Lattice anharmonicity driven by weakening interatomic interactions inherits an intrinsically low lattice thermal conductivity in a crystal. In this work, we demonstrate the efficacy of V (hole-doping) and Fe (electron-doping) co-substitutions on the Mn-sites for realizing charge compensation and lattice anharmonicity in p-type higher manganese silicide (HMS) single crystals melt grown employing the Bridgman method. A higher power factor sustained by optimal valence electron count (VEC) through charge compensation along with a significant reduction in lattice thermal conductivity promoted by local ordering or atomic clustering-induced lattice anharmonicity has enabled the attainment of an unprecedentedly higher thermoelectric figure-of-merit (zT) ∼0.75 (±0.1) at 873 K in partially substituted (Mn0.94V0.03Fe0.03)Si1.74 single crystals, corresponding to ∼300% enhancement over pristine MnSi1.74. The inherent structural modulation and incommensurate periodicities were assessed employing the Le Bail analysis within the framework of a (3 + 1)-dimensional superspace approach and interpreted by following the 14-electron rule for Nowotny chimney ladder phases to reveal the structure–property correlations. These findings provide a greater understanding of the interrelations between crystal structure, chemical bonding, and lattice dynamics in HMSs, a prominent example of the Nowotny chimney ladder phase for thermoelectric applications. [ABSTRACT FROM AUTHOR]

Grain boundary (GB) scattering has been widely reckoned as a primary restraint on room-temperature (RT) carrier mobility in Mg3Sb2-based materials. In this work, two-dimensional graphene (G) with varied contents was added to single phase Mg3.24Sb1.5Bi0.49Te0.01 materials in order to tailor the highly resistive space-charge region at GBs. The results indicate that introducing G effectively lowers the carrier transport energy barrier Eb from 42 meV (pristine sample) to 18 meV (Mg3.24Sb1.5Bi0.49Te0.01/1.0 vol% G sample), and correspondingly increases the drift mobility by 112.5% from 32 cm2 V−1 s−1 to 68 cm2 V−1 s−1 at RT, leading to an enhanced power factor and thus ZT value. Besides, first-principles calculations were also performed to qualitatively bridge the underlying negative correlation between the electronic density of states (DOS) and GB potential barrier Eb. Moreover, the equivalent nano-particle phonon scattering is also realized through introducing the two-dimensional G, contributing to a moderate reduction in lattice thermal conductivity as quantitatively illustrated based on the Debye–Callaway model. Consequently, the figure of merit ZT for G-added samples is greatly improved in the entire temperature range compared with that of the G-free sample. This study opens up a new avenue for rationally engineering the grain boundary, via regulating interfacial electronic DOS, to optimize electrical transport properties and ZT values. [ABSTRACT FROM AUTHOR]

We have conducted a computer simulation of thermoelectric (TE) properties in tilted Cu / Fe 2 V (Al 0.9 Si 0.1) multilayers. Such a tilted configuration yields a transverse (off-diagonal) TE effect whereby an electric current can flow perpendicularly to the temperature gradient. Appropriately controlling the relative Cu thickness and the tilting angle realizes a higher power factor than that of the parent TE materials. In our multilayers, the estimated power factor exceeds 8 mW / K 2 m , being approximately three times higher than that of the parent TE materials. On the basis of the simulation results, we have fabricated several modules and achieved a maximum power of 4.83 mW in the module with a relative Cu thickness of 0.7 and a tilting angle of 30 °. [ABSTRACT FROM AUTHOR]

Efficiently decreasing the lattice thermal conductivity, κ L , is one of the main concerns in the field of thermoelectrics (TE). Herein, we theoretically investigate κ L for single-crystal and polycrystalline CrSi 2 using first-principles and the phonon Boltzmann transport equation. Though CrSi 2 is known as a potential TE material because of its reasonable power factor, controlling its κ L remains as a challenge to be solved. In this study, we discuss how to decrease κ L efficiently on the basis of the calculation. The phonon band structure and density of states are computed via harmonic calculation. In addition, the achievable lowest lattice thermal conductivity, κ L 0 , and cumulative lattice thermal conductivity, κ cum , are estimated using the Cahill model and anharmonic calculation, respectively. We predict κ L 0 for CrSi 2 to be around 2.2 W m − 1 K − 1 at 650 K, which suggests that CrSi 2 is a potential TE material with high z T over 0.39 at 650 K. The phonon mean-free path dependence of κ cum indicates that the critical crystallite size for decreasing κ L for polycrystalline CrSi 2 is 70 nm at 600 K. In addition, it is revealed that the crystallite size should be as small as 7 nm to decrease κ L to half. These calculational findings offer useful insights into how to control κ L for CrSi 2. [ABSTRACT FROM AUTHOR]

Lattice defect engineering has attracted attention due to its ability to develop thermoelectric materials with low thermal conductivity. For Mg2Si single crystals (SCs), Si vacancy (VSi) defects can be introduced and consequently result in the formation of dislocation cores. These lattice defects confer Mg2Si SCs with a lower thermal conductivity compared to Mg2Si polycrystals. To reveal a mechanism for the stabilisation of VSi in the Mg2Si SCs, we investigated the effects of oxygen (O) on lattice defects by performing electronic structure calculations, secondary ion mass spectrometry, X-ray photoelectron spectroscopy, and photoelectron holography. On the basis of these calculations, we predicted that O stabilised the formation of VSi when it was located at the Si site or at an interstitial site. All experiments confirmed the presence of O inside the Mg2Si SCs. However, O was suggested to be located not at the specific site in the crystal lattice of Mg2Si but at dislocation cores. The interaction between O and the dislocation cores in the Mg2Si SC is expected to immobilise dislocation cores, leading to the stabilisation of VSi formation. [ABSTRACT FROM AUTHOR]

Mg2Sn is a promising mid-temperature thermoelectric (TE) material consisting of earth-abundant, low-cost, and non-toxic elements. Currently, the TE performance of p-type Mg2Sn is still poor due to a lower power factor (PF) and a higher lattice thermal conductivity (κlat) than those of n-type Mg2Sn. To overcome these disadvantages, we synthesized Li-doped Mg2Sn single crystals (SCs) by the melting method. Li-doping successfully changed the conduction of the Mg2Sn SC from an n-type to a p-type. The Li-doped Mg2Sn SCs contain Mg vacancies, dislocation cores, and Sn-rich precipitates. These multi-scale defects in the Li-doped Mg2Sn SCs did not deteriorate carrier mobility and they effectively scattered phonons with a wide range of frequencies. Since grain boundaries did not exist in the Li-doped Mg2Sn SCs, higher carrier mobility and PF were achieved compared with other p-type Mg2Sn polycrystals (PCs) and SCs. Moreover, the κlat of the Li-doped Mg2Sn SC was lower than that of p-type Mg2Sn PCs and SCs. Owing to the enhanced PF and reduced κlat, a maximum dimensionless figure-of-merit zT of ∼0.38 at 700 K was achieved for the p-type Li-doped Mg2Sn SC with a Li content of 2.5%, the highest value for a p-type Mg2Sn ever reported. [ABSTRACT FROM AUTHOR]

Filled-skutterudite materials are promising candidates for thermoelectric applications in the intermediate-temperature range to recover waste heat. In this work, mechanical alloying and spark plasma sintering (SPS) techniques were used to consolidate double-filling InxLa0.25Co4Sb12 (x = 0, 0.1, 0.3, 0.5) samples. X-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy were used to analyze the microstructure of the InxLa0.25Co4Sb12 SPS-ed samples. The microstructure results revealed the main phase of the CoSb3 skutterudite structure with a small amount of InSb and CoSb2 attributed to secondary phases. Electrical resistivity remarkably decreased to 9.7 μΩ m at room temperature for the In0.5La0.25Co4Sb12 sample, mainly due to the effective impurity of the InSb nanoinclusions. Moreover, the InSb nanoinclusions yielded a substantial depression in lattice thermal conductivity due to phonon scattering. The reduction in lattice thermal conductivity was approximately 62% for the In0.5La0.25Co4Sb12 sample compared with the La0.25Co4Sb12 sample, resulting in a remarkable enhancement in the dimensionless figure-of-merit (ZT) of 1.25. [ABSTRACT FROM AUTHOR]

Iron‐based half‐Heusler alloys constitute an emerging class of semiconducting intermetallics for scalable and efficient thermoelectric conversion, owing to their remarkably high‐power factor, abundance, and low cost. This review encompasses the recent advances in materials synthesis and evolving aspects of optimization pathways in pre‐existing Fe‐based half‐Heusler compositions for attaining a higher thermoelectric figure of merit (zT). The experimental outcomes and theoretical predictions were analyzed and compared using a parametric framework to understand the underlying electronic transport responsible for high power factors exhibited by most of these alloys distinctively. Alongside, effective microstructural approaches were reviewed for which favorable reduction in intrinsically high lattice thermal conductivity (κL) was attained. The electronic structures of MFeSb (M=V, Nb, and Ta) half‐Heuslers is also analyzed using density functional theory‐based calculations to understand the origin of favorable conduction and electrical transport properties. Finally, processing‐structural‐property correlations are discussed to highlight the relevance of structural ordering, phase transformation, and defects on transport properties, for developing effective strategies and material design in Fe‐based half‐Heuslers for their development in thermoelectrics. [ABSTRACT FROM AUTHOR]