Optimization of thermoelectric performance of SrSi2-based alloys via the modification in band structure and phonon-point-defect scattering

Kuo, Y. K.; Balakrishnan, R.; Lue, Chin Shan

doi:10.3389/fchem.2014.00106

Cited by 41 publications

(38 citation statements)

References 41 publications

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“…In general, the major difficulty in obtaining good thermoelectric performance of materials is to enhance the power factor (P F = S 2 /ρ) while simultaneously reducing κ [38][39][40][41]. For Ru 1.95 Ta 1.05 Al, we found that the room-temperature κ is suppressed to about 3.8 W/mK, as indicated in Fig.…”

Section: A Electrical Transport and Thermoelectric Propertiesmentioning

confidence: 63%

Semimetallic behavior in Heusler-type Ru2TaAl and thermoelectric performance improved by off-stoichiometry

et al. 2017

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We report a study of the temperature-dependent electrical resistivity, Seebeck coefficient, thermal conductivity, specific heat, and 27 Al nuclear magnetic resonance (NMR) in Heusler-type Ru 2 TaAl, to shed light on its semimetallic behavior. While the temperature dependence of the electrical resistivity exhibits semiconductorlike behavior, the analysis of low-temperature specific heat reveals a residual Fermi-level density of states (DOS). Both observations can be realized by means of a semimetallic scenario with the Fermi energy located in the pseudogap of the electronic DOS. The NMR Knight shift and spin-lattice relaxation rate show activated behavior at higher temperatures, attributing to the thermally excited carriers across a pseudogap in Ru 2 TaAl. From the first-principles band structure calculations, we further provide a clear picture that an indirect overlap between electron and hole pockets is responsible for the formation of a pseudogap in the vicinity of the Fermi level of Ru 2 TaAl. In addition, an effort for improving the thermoelectric performance of Ru 2 TaAl has been made by investigating the thermoelectric properties of Ru 1.95 Ta 1.05 Al. We found significant enhancements in the electrical conductivity and Seebeck coefficient and marked reduction in the thermal conductivity via the off-stoichiometric approach. This leads to an increase in the figure-of-merit ZT value from 6.1 × 10 −4 in Ru 2 TaAl to 3.4 × 10 −3 in Ru 1.95 Ta 1.05 Al at room temperature. In this respect, a further improvement of thermoelectric performance based on Ru 2 TaAl through other off-stoichiometric attempts is highly probable.

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Section: A Electrical Transport and Thermoelectric Propertiesmentioning

confidence: 63%

Semimetallic behavior in Heusler-type Ru2TaAl and thermoelectric performance improved by off-stoichiometry

et al. 2017

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“…The specific heat data for these SMAs were obtained using a high-resolution ac calorimeter with chopped light as a heat source. More details about these measurement techniques can be obtained elsewhere 25 – 28 , 38 . The presented electrical and thermal measurement systems are all equipped with a calibrated silicon diode thermometer (Lake Shore model DT-470-SD) and all data presented in the manuscript were recorded with a slow heating rate of about 20 K/h and reproducibility better than 2%.…”

Section: Methodsmentioning

confidence: 99%

Characteristics of martensitic and strain-glass transitions of the Fe-substituted TiNi shape memory alloys probed by transport and thermal measurements

Balakrishnan

Chang

Kuo

et al. 2017

Sci Rep

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The electrical resistivity, Seebeck coefficient, thermal conductivity, and specific heat of Ti50Ni50-xFex (x = 2.0–10.0 at.%) shape memory alloys (SMAs) were measured to investigate the influence of point defects (Fe) on the martensitic transformation characteristics. Our results show that the Ti50Ni48Fe2 and Ti50Ni47Fe3 SMAs have a two-step martensitic transformation (B2 → R and R → B19′), while the Ti50Ni46Fe4, Ti50Ni44.5Fe5.5, and Ti50Ni44Fe6 SMAs display a one-step martensitic transition (B2 → R). However, the compounds Ti50Ni42Fe8 and Ti50Ni40Fe10 show strain glass features (frozen strain-ordered state). Importantly, the induced point defects significantly alter the martensitic transformation characteristics, namely transition temperature and width of thermal hysteresis during the transition. This can be explained by the stabilization of austenite B2 phase upon Fe substitution, which ultimately leads to the decrease in enthalpy that associated to the martensitic transition. To determine the boundary composition that separates the R-phase and strain glass systems in this series of SMAs, a Ni-rich specimen Ti49Ni45Fe6 was fabricated. Remarkably, a slight change in Ti/Ni ratio converts Ti49Ni45Fe6 SMA into a strain glass system. Overall, the evolution of phase transformation in the Fe-substituted TiNi SMAs is presumably caused by the changes in local lattice structure via the induced local strain fields by Fe point defects.

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“…The double-WSM state has been predicted recently in the inversion-asymmetric chiral compound strontium disilicide, SrSi 2 , through band structure calculations [44]. This is an interesting material because it is composed of non-toxic and naturally abundant elements, and it has been known for decades as a promising candidate for thermoelectric applications through chemical substitution [48][49][50][51][52][53]. The double-Weyl nodes in SrSi 2 are generated via a band inversion mechanism, and lie along the C 4 rotation axis as seen in Figs.…”

Section: Introductionmentioning

confidence: 99%

“…The experimental situation with SrSi 2 , however, remain uncertain. Early transport measurements [53] reported SrSi 2 to be a narrow band gap (10 ∼ 30 meV) semiconductor, while more recent experiments find it to be a gapless semimetal [50,51]. Other experimental studies focusing on thermoelectric properties show that the semimetal state of SrSi 2 could be stabilized through chemical substitution of Sr by the lighter Ca atoms [50,51].…”

Section: Introductionmentioning

confidence: 99%

Tunable double-Weyl Fermion semimetal state in the SrSi2 materials class

Singh¹,

Chang²,

Chang³

et al. 2018

Sci Rep

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We discuss first-principles topological electronic structure of noncentrosymmetric SrSi2 materials class based on the hybrid exchange-correlation functional. Topological phase diagram of SrSi2 is mapped out as a function of the lattice constant with focus on the semimetal order. A tunable double-Weyl Fermion state in Sr1−xCaxSi2 and Sr1−xBaxSi2 alloys is identified. Ca doping in SrSi2 is shown to yield a double-Weyl semimetal with a large Fermi arc length, while Ba doping leads to a transition from the topological semimetal to a gapped insulator state. Our study indicates that SrSi2 materials family could provide an interesting platform for accessing the unique topological properties of Weyl semimetals.

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Optimization of thermoelectric performance of SrSi2-based alloys via the modification in band structure and phonon-point-defect scattering

Cited by 41 publications

References 41 publications

Semimetallic behavior in Heusler-type Ru2TaAl and thermoelectric performance improved by off-stoichiometry

Semimetallic behavior in Heusler-type Ru2TaAl and thermoelectric performance improved by off-stoichiometry

Characteristics of martensitic and strain-glass transitions of the Fe-substituted TiNi shape memory alloys probed by transport and thermal measurements

Tunable double-Weyl Fermion semimetal state in the SrSi2 materials class

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