Large thermoelectric power factor in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">TiS</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>crystal with nearly stoichiometric composition

Imai, Hideto; Shimakawa, Yuichi; Kubo, Yoshimi

doi:10.1103/physrevb.64.241104

Cited by 177 publications

(127 citation statements)

References 25 publications

(37 reference statements)

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“…Therefore, we proposed the idea of a 'natural superlattice' produced by intercalating a layer of SnS into the van der Waals gap of layered TiS 2 [29,30]. The TiS 2 layer can provide thermopower as well as the electron pathway according to Imai's research on TiS 2 single crystals [31]. The intercalated SnS layer can suppress the transport of phonons as a consequence of the interaction between the SnS layer and TiS 2 layer and/or disruption of the periodicity [18], CsBi 4 Te 6 [14], Tl 9 BiTe 6 [9], silicon nanowires [21], LaFe 3 CoSb 12 [12] and ErAs embedded in the InGaAlAs matrix [34].…”

Section: The Concept Of 'Natural Superlattice'mentioning

confidence: 99%

Development of novel thermoelectric materials by reduction of lattice thermal conductivity

Wan

Wang

et al. 2010

Science and Technology of Advanced Materials

146

120

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Thermal conductivity is one of the key parameters in the figure of merit of thermoelectric materials. Over the past decade, most progress in thermoelectric materials has been made by reducing their thermal conductivity while preserving their electrical properties. The phonon scattering mechanisms involved in these strategies are reviewed here and divided into three groups, including (i) disorder or distortion of unit cells, (ii) resonant scattering by localized rattling atoms and (iii) interface scattering. In addition, we propose construction of a 'natural superlattice' in thermoelectric materials by intercalating an MX layer into the van der Waals gap of a layered T X 2 structure which has a general formula of (M X ) 1+x (T X 2 ) n (M = Pb, Bi, Sn, Sb or a rare earth element; T = Ti, V, Cr, Nb or Ta; X = S or Se and n = 1, 2, 3). We demonstrate that one of the intercalation compounds (SnS) 1.2 (TiS 2 ) 2 has better thermoelectric properties compared with pure TiS 2 in the direction parallel to the layers, as the electron mobility is maintained while the phonon transport is significantly suppressed owing to the reduction in the transverse phonon velocities.

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Section: The Concept Of 'Natural Superlattice'mentioning

confidence: 99%

Development of novel thermoelectric materials by reduction of lattice thermal conductivity

Wan

Wang

et al. 2010

Science and Technology of Advanced Materials

146

120

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“…Previous experimental studies [12] have reported that nearly stoichiometric TiS 2 shows a large power factor value of 37.1 µW/K 2 -cm at room temperature that is comparable with the best thermoelectric material Bi 2 Te 3 [13]. The large power factor originates from a sharp increase in the density of states just above the Fermi energy as well as the inter-valley scattering of charge carriers [12,14,15]. However, the semimetallic nature of TiS 2 gives rise to bipolar effects which are not desirable for thermoelectric applications [16].…”

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confidence: 99%

Strain-induced electronic phase transition and strong enhancement of thermopower ofTiS2

2014

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Using first principles density functional theory calculations, we show a semimetal to semiconducting electronic phase transition for bulk TiS2 by applying uniform biaxial tensile strain. This electronic phase transition is triggered by charge transfer from Ti to S, which eventually reduces the overlap between Ti-(d) and S-(p) orbitals. The electronic transport calculations show a large anisotropy in electrical conductivity and thermopower, which is due to the difference in the effective masses along the in-plane and out of plane directions. Strain induced opening of band gap together with changes in dispersion of bands lead to three-fold enhancement in thermopower for both p-and n-type TiS2. We further demonstrate that the uniform tensile strain, which enhances the thermoelectric performance, can be achieved by doping TiS2 with larger iso-electronic elements such as Zr or Hf at Ti sites. [7]. Among the TMDs, TiS 2 has been in focus of extensive research due to its potential applications as cathode materials for lithium-ion batteries [8][9][10][11]. Previous experimental studies [12] have reported that nearly stoichiometric TiS 2 shows a large power factor value of 37.1 µW/K 2 -cm at room temperature that is comparable with the best thermoelectric material Bi 2 Te 3 [13]. The large power factor originates from a sharp increase in the density of states just above the Fermi energy as well as the inter-valley scattering of charge carriers [12,14,15]. However, the semimetallic nature of TiS 2 gives rise to bipolar effects which are not desirable for thermoelectric applications [16].The electronic structure of TiS 2 is very unique and even a slight change can significantly influence thermoelectric properties. It has been shown that 0.04% Mg doping at Ti-site in TiS 2 causes a 1.6 times increase in thermopower at 300 K [17]. Recently, it has been discovered that the electronic structures of semiconducting TMDs (MX 2 (M = Mo, W; X=S, Se, Te)) are very sensitive to the applied pressure/strain, which causes an electronic phase transition from semiconductor to metal [18][19][20][21]. Also few layers and mono-layer TMDs show wide range of tunability in electronic and magnetic properties by application of strain [22][23][24][25][26]. Contrary to that, TiS 2 remains semimetallic up to a compressive hydrostatic pressure of 20 GPa [27]. So far there has been no studies on effect of uniform tensile strain on the electronic properties of TiS 2 . Here, we carry out a study of the electronic structure of TiS 2 as a function of applied uniform biaxial tensile strain (BTS). The material undergoes electronic phase transition from semimetal to a small band gap (< 0.15 eV) semiconductor. Most interestingly, the semiconducting strained TiS 2 exhibits nearly a four-fold enhancement in thermopower compared to the unstrained phases. We also explore the possibility of generating such a strain by doping with larger atoms at Ti sites. Iso-electronic Hf and Zr turn out to be the best dopants to generate the 2% tensile strain producing the same...

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“…Layered TiS 2 (titanium disulfide), one type of thermoelectric materials, has been reported to show a high power factor at room temperature but shows a low thermoelectric figure of merit, ZT (=S 2 ·T/¬, where S is Seebeck coefficient, · electrical conductivity, T the absolute temperature, and ¬ thermal conductivity), because of its high thermal conductivity. 1) Various efforts have been reported to reduce its thermal conductivity and one successful approach is forming a (SnS) 1.2 (TiS 2 ) 2 natural superlattice by intercalating an SnS layer into the TiS 2 Van der Waals gaps. The thermal conductivity was found to be reduced due to the softening of the transverse phonon velocity because of weakening of interlayer bonding by the intercalated SnS layer and a ZT value of 0.37 at 700 K was attained.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of layered TiS2-based thermoelectric elements fabricated by a centrifugal heating technique

Aoki

Wan

Ishiguro

et al. 2011

J. Ceram. Soc. Japan

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We have developed a centrifugal heating apparatus to fabricate layered TiS 2 -based thermoelectric elements, and evaluated their thermoelectric properties. We found that layered (SnS) 1.2 (TiS 2 ) 2 bulk elements with preferred crystallographic orientation can be produced within a quartz tube under a centrifugal acceleration of 1,000 g or higher and at a maximum temperature of 1,073 K or higher. With the increasing centrifugal acceleration from 1,000 to 8,000 g, the electrical conductivity of the produced specimen was almost doubled possibly because of the increased degree of crystal-axis orientation. For the specimens produced at 8,000 g, we estimated a maximum thermoelectric figure of merit, ZT, of approximately 0.2 (673 K). We have thus demonstrated that it is possible to use the centrifugal heating technique to fabricate layered TiS 2 -based thermoelectric elements directly from the powdered raw materials.

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Large thermoelectric power factor inTiS2crystal with nearly stoichiometric composition

Cited by 177 publications

References 25 publications

Development of novel thermoelectric materials by reduction of lattice thermal conductivity

Development of novel thermoelectric materials by reduction of lattice thermal conductivity

Strain-induced electronic phase transition and strong enhancement of thermopower ofTiS2

Evaluation of layered TiS2-based thermoelectric elements fabricated by a centrifugal heating technique

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