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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]

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]

A single‐phase sample of α′ (O′3)‐type layered sodium cobalt oxide NaxCoO2 (x ∼ 0.78) was prepared and its incommensurately modulated crystal structure was analyzed using the (3+1)‐dimensional superspace approach to the powder neutron diffraction data. The crystal structure of the cobaltate is accurately described based on the superspace group C2/m(α0γ)00, wherein the positions of Na atoms are most significantly modulated in the monoclinic a direction to form an ordered arrangement. Such a displacive modulation causes a quasi‐periodic shift of Na atoms from the centers of the NaO6 polyhedra between undulated CoO2 sheets, changing the form of the NaO6 polyhedron from an octahedral coordination (O) to a trigonal prismatic (P) one, via an intermediate capped trigonal prismatic NaO7 coordination (C). At the positions where the Na atoms are most significantly shifted, the neighboring Na atoms are located at almost touching distances. However, the occupation factor of Na atoms becomes zero at such positions, yielding Na‐deficient sites VNa, sandwiched either between C and P, or C and C‐type polyhedra. [ABSTRACT FROM AUTHOR]

Mg3Sb2‐based intermetallic compounds with exceptionally high thermoelectric performance exhibit unconventional n‐type dopability and anomalously low thermal conductivity, attracting much attention to the underlying mechanisms. To date, investigations have been limited to first‐principle calculations and thermodynamic analysis of defect formation, and detailed experimental analysis on crystal structure and phonon modes has not been achieved. Here, a synchrotron X‐ray diffraction study clarifies that, against a previous view of a simple crystal structure with a small unit cell, Mg3Sb2 is inherently a heavily disordered material with Frenkel defects, charge‐neutral defect complexes of cation vacancies and interstitials. Ionic charge neutrality preserved in Mg3Sb2 is responsible for exotic n‐type dopability, which is unachievable for other Zintl phase materials. The thermal conductivity of Mg3Sb2 exhibits deviation from the standard T−1 temperature dependency with strongly limited phonon transport due to a strain field. Inelastic X‐ray scattering measurement reveals enhanced phonon scattering induced by disorder. The results will draw renewed attention to crystal defects and disorder as means to explore new high‐performance thermoelectric materials. [ABSTRACT FROM AUTHOR]

The structural and pyroelectric properties of partially Ca‐substituted BaTiO3, Ba1−xCaxTiO3 (0 ≤ x ≤ 0.2), are investigated. Partial Ca‐substitution in BaTiO3 introduced tetragonal distortion in the TiO6 octahedrons and increased the displacement, Δd, of a Ti4+ cation from the center of an octahedron. This increase in Δd led to enhancement of remanent polarization and pyroelectric voltage, Vp. The pyroelectric energy storage behavior is demonstrated for the partially Ca‐substituted BaTiO3. For the Ba0.9Ca0.1TiO3 sample which exhibited the highest Vp, the stored energy in an output capacitor was proven to be sufficient to operate micropower Internet of Things devices. [ABSTRACT FROM AUTHOR]

Crystal structure and thermoelectric properties of an organic compound of tetrathiafulvalene (TTF) and iodine (I), TTF-I0.71, were investigated. From X-ray diffraction of TTF-I0.71 powder prepared by a solid state reaction, the superspace group of TTF-I0.71 was determined as C2/ m( p0 r)0 s. The TTF-I x thin films were also fabricated on a glass substrate. It was found that the actual composition x increased with film thickness, and reached to approximately 0.72 above 300 nm. The Seebeck coefficient and electrical conductivity of the films showed time-dependent change, due to the homogenization of iodine concentration in the film. [ABSTRACT FROM AUTHOR]

Metal oxides (Ca3Co4O9, CaMnO3, SrTiO3, In2O3), Ti sulfides, and Mn silicides are promising thermoelectric (TE) material candidates for cascade-type modules that are usable in a temperature range of 300-1200 K in air. In this paper, we review previous studies in the field of TE materials development and make recommendations for each material regarding future research. Furthermore, the R&D of TE modules composed of metal oxide materials and the prospect of their commercialization for energy harvesting is demonstrated. [ABSTRACT FROM AUTHOR]

The structural and pyroelectric properties of partially Ca‐substituted BaTiO3, Ba1−xCaxTiO3 (0 ≤ x ≤ 0.2), are investigated. Partial Ca‐substitution in BaTiO3 introduced tetragonal distortion in the TiO6 octahedrons and increased the displacement, Δd, of a Ti4+ cation from the center of an octahedron. This increase in Δd led to enhancement of remanent polarization and pyroelectric voltage, Vp. The pyroelectric energy storage behavior is demonstrated for the partially Ca‐substituted BaTiO3. For the Ba0.9Ca0.1TiO3 sample which exhibited the highest Vp, the stored energy in an output capacitor was proven to be sufficient to operate micropower Internet of Things devices. [ABSTRACT FROM AUTHOR]