Lattice anharmonicity in charge compensated higher manganese silicide single crystals

Chauhan, Nagendra S.; Ono, Ichiro; Miyazaki, Yasumitsu

doi:10.1039/d3ta02985a

Cited by 3 publications

(1 citation statement)

References 43 publications

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“…Different compositions or stoichiometries of HMSs may coexist incommensurately among which Nowotny Chimney Ladder (NCL) phases are distinctively identified, which constitute of two tetragonal subsystems of [Mn] and [Si] having an incommensurate c -axis, wherein Si atoms forming a ladder are enclosed by Mn atoms arranged as a chimney. , Having an odd stoichiometry, these silicon-rich NCL phases are denoted by MnSi γ , wherein γ as the component of modulation vector (00γ) is defined using c -axis length ratio γ = c Mn / c Si of [Mn] and [Si] subsystems. , Stoichiometrically, γ corresponds to odd Si/Mn stoichiometry and has been found to vary in the range of 1.72 to 1.75, which depends on several factors such as the nominal composition, dopant, thermal history, and synthesis methodology. ,− The accurate evaluation of structural parameters modulated by inherent incommensurability in HMS alloys is possible within the theoretical framework of the (3 + 1)-dimensional superspace approach, which characteristically reveals that γ can be varied favorably by choosing the appropriate dopants to alter γ favorably. − …”

Section: Introductionmentioning

confidence: 99%

Discordant Doping and Labile Silicon Atoms in Higher Manganese Silicide

Chauhan,

Miyazaki

2023

ACS Appl. Energy Mater.

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Discordant doping is broadly connoted to atomic substitutions wherein even a marginal amount of incoming atom is unable to adopt the local geometry of the site it occupies and gets inhomogeneously distributed within the crystal. Herein, we report the implication of partial B or Ge doping on the labile, i.e., easily altered, Si atoms of higher manganese silicide (MnSi γ ), prepared by spark plasma sintering of melt-spun ribbons. The synthesized Mn(Si 1−x D x ) γ alloys (where D = B or Ge are dopants) having a Nowotny chimney ladder (NCL) phase, showed a close relation of their structural stability and electrical transport properties to the 14-electron rule. Following the (3 + 1) dimensional superspace approach, the modulation vector component (γ) was accurately determined and correlated with the electrical transport and valence electron count (VEC) of the synthesized samples. Beyond the solubility limit of B/Ge onto the labile [Si] subsystem, a homogeneous formation of Si-rich domains and (Si, Ge) solid solution within the MnSi γ matrix was distinctively observed for B and Ge doping, respectively, which modifies the thermal and electrical transport properties. Comparatively, Ge doping was more favorable than B doping on the Si sites of MnSi γ , wherein the peak thermoelectric figure of merit (zT) ∼ 0.67 (±0.1) at 823 K was obtained for Mn(Si 0.99 Ge 0.01 ) γ , corresponding to ∼50% enhancement, when compared to the Ge-doped HMS single-crystal counterparts.

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Section: Introductionmentioning

confidence: 99%

Discordant Doping and Labile Silicon Atoms in Higher Manganese Silicide

Chauhan,

Miyazaki

2023

ACS Appl. Energy Mater.

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Odd‐Stoichiometry and Secondary Phase Relations in Higher Manganese Silicides

Chauhan,

Sara,

Bhattacharya

et al. 2024

Adv Funct Materials

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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.

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Higher manganese silicides: A Nowotny chimney ladder phase for thermoelectric applications

Chauhan,

Miyazaki

2023

Chemical Physics Reviews

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Nowotny chimney ladder (NCL) phases are intermetallic binary compounds that typically crystallize in a tetragonal crystal structure and constitute of two separate subsystems. The rich solid-state chemistry of NCL phases inherits fascinating lattice dynamics with unique abilities for structural modifications. As an extensively studied energy material for the thermoelectric application, we overview the emerging aspects for structural interpretation in higher manganese silicides (MnSiγ), a prominently explored example of NCL phase. The progress in understanding the incommensurate composite crystals of MnSiγ is discussed to highlight its functional crystallography for proposing the effective strategies to attain favorable modification of transport properties of charge carriers (concentration, mobility, effective mass), and phonons (lattice thermal conductivity). The application potential and prospective strategies for enabling the rational optimization of the dimensionless thermoelectric figure of merit (zT) are examined, and the possibilities of chemical modification in MnSiγ and related NCL phases are presented.

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Lattice anharmonicity in charge compensated higher manganese silicide single crystals

Abstract: 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)...

Cited by 3 publications

References 43 publications

Discordant Doping and Labile Silicon Atoms in Higher Manganese Silicide

Discordant Doping and Labile Silicon Atoms in Higher Manganese Silicide

Odd‐Stoichiometry and Secondary Phase Relations in Higher Manganese Silicides

Higher manganese silicides: A Nowotny chimney ladder phase for thermoelectric applications

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