Electronic specific heat of Ti1+xS2 (0 &lt; x &lt; 0.1)

Kobayashi, Hisao; Sakashita, Keiji; Sato, Masaki; Nozue, Tatsuhiro; Suzuki, Takashi; Kamimura, Takashi

doi:10.1016/s0921-4526(97)00086-0

Cited by 15 publications

(11 citation statements)

References 3 publications

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“…Similarly, the lattice parameter a decreases firstly from 3.4077 Å to 3.3998 Å as the cobalt content x increases from 0 to 0.20, and then a increases to 3.4067 Å for x = 0.30. Many investigations [25][26][27][28] have shown that the lattice parameter a of the intercalated compounds M y TiS 2 (where M stands for intercalated elements) is always found to increase with increasing content of intercalated elements. (For example, the lattice parameter a changed from 3.4083 Å to 3.4156 Å in Bi y TiS 2 25 with y increasing from 0 to 0.25; the parameter a of Li y TiS 2 27 changed from 3.407 Å to 3.452 Å with increasing y from 0 to 1.0; the parameter a of self-intercalated compound Ti 1+y S 2 28 increased from 3.405 Å to 3.412 Å with y increasing from 0 to 0.1; see Table I.)…”

Section: Resultsmentioning

confidence: 99%

“…11 However, in practice, self-intercalation of Ti into TiS 2 is unavoidable in the synthesis process. 28 As a result, TiS 2 almost always appears as an extrinsic semiconductor. Moreover, if the ionization energy of self-intercalated Ti atoms is small enough, complete ionization will occur at the low temperatures that can normally be reached.…”

Section: Effects Of Co Doping On DC Resistivitymentioning

confidence: 99%

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Thermoelectric Properties of Co-Doped TiS2

Zhang

Qin

Xin

et al. 2011

Journal of Elec Materi

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The thermoelectric properties of cobalt-doped compounds Co x Ti 1Àx S 2 (0 £ x £ 0.3) prepared by solid-state reaction were investigated from 5 K to 310 K. It was found that the electric resistivity q and absolute thermopower |S| for all the doped compounds decreased significantly with increasing Co content over the whole temperature range investigated. The increased lattice thermal conductivity of the doped compounds would imply enhancement of the acoustic velocity. Moreover, the ZT value of the doped compounds was improved over the whole temperature range investigated, and specifically reached 0.03 at 310 K for Co 0.3 Ti 0.7 S 2 , being about 66% larger than that of TiS 2 . INTRODUCTIONTiS 2 has an anisotropic structure with a trigonal space group, P " 3m1. It is known to exist in two polytypes (1T, 2H) with octahedral and trigonalprismatic coordinations, respectively. The main difference between the 1T-TiS 2 and 2H-TiS 2 layers is the type of local coordination of the metal: octahedral (1T) versus trigonal-prismatic (2H) 1 (Fig. 1). The most stable form of TiS 2 (1T-TiS 2 , crystallizing in a layered CdI 2 -like structure) consists of sheets of face-sharing TiS 6 octahedra forming S-Ti-S sandwich layers, where a Ti sheet is sandwiched between two sulfur sheets. Atoms within S-Ti-S sheets are bound by strong covalent interactions, whereas bonding between the layers is determined by weak, van der Waals forces.Although the structure of TiS 2 is quite simple, the nature of the electronic structure of layered TiS 2 has been in dispute over the past decades. To date, for instance, whether it is a semiconductor or semimetal has not been clarified. 2-16 Through measurements of the Hall coefficient, Seebeck coefficient, and resistivity as a function of pressure, Klipstein and Friend 2 found that the band overlap between S 3p states and Ti 3d states increased at a rate of 4.5 meV/kbar, and concluded that TiS 2 is a semiconductor with a gap of 0.18 ± 0.06 eV. The optical measurements of Greenway and Nische 3 indicated that TiS 2 is a semiconductor with a gap of 1 eV to 2 eV. Chen et al. 4 and Barry et al. 5 reported a band gap of about 0.3 eV from angle-resolved photoemission studies (ARPS). Photoemission experiments by Shepherd and Williams 6 indicate a band gap of less than 0.5 eV, and calculations using the pseudopotential (PP) method 7 indicated that TiS 2 is a semiconductor with an indirect band gap of about 2 eV. On the contrary, some theoretical calculations indicate that TiS 2 is a semimetal. Lately, Benesh et al. 8 obtained a semimetallic ground state for TiS 2 by using the linearized augmented plane wave (LAPW) method as a function of pressure. Similarly, band calculations based on the augmented spherical wave (ASW) method by Fang et al., 9 the linear muffin-tin orbital (LMTO) method by Wu et al., [10][11][12] and the full-potential (FP)-LAPW method 13,14 showed that TiS 2 possessed a semimetallic ground state. Meanwhile, many experiments 15,16 have indicated that the electrical resistivity of TiS 2 almost excl...

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Section: Resultsmentioning

confidence: 99%

Section: Effects Of Co Doping On DC Resistivitymentioning

confidence: 99%

Thermoelectric Properties of Co-Doped TiS2

Zhang

Qin

Xin

et al. 2011

Journal of Elec Materi

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“…The accurate lattice parameters were determined from the d values of the XRD peaks using a standard least-squares refinement method with a Si standard for calibration. Many investigations [26][27][28] showed that lattice parameter a of the intercalated compounds M y TiS 2 ͑here M stands for intercalated elements͒ was always found to increase with increasing content of intercalated elements ͑for example, lattice parameter a changed from 3.4083 to 3.4156 Å in Bi y TiS 2 ͑Ref. One can see from Fig.…”

Section: Methodsmentioning

confidence: 99%

The effect of Mg substitution for Ti on transport and thermoelectric properties of TiS2

Qin

Zhang

et al. 2007

Journal of Applied Physics

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Magnesium substituted compounds Mg x Ti 1−x S 2 ͑0 ഛ x ഛ 0.15͒ were prepared by solid-state reaction, and their transport and thermoelectric properties were investigated from 5 to 310 K. The results indicate that at low temperatures ͑T Ͻ ϳ 175 K͒, a transition from metallike to semiconductorlike behavior occurred after the substitution of Mg for Ti, which implies that intrinsically TiS 2 is a semiconductor and this transition can be ascribed to de-degeneration through the reduction in electron concentration due to Mg 2+ substitution for Ti 4+ . Furthermore, it was found that dc conductivity for Mg x Ti 1−x S 2 ͑x Ͼ 0͒ obeyed Mott's two-dimensional ͑2D͒ variable range hopping law ln ϰ T −1/3 at T Ͻ ϳ 50 K, indicating that TiS 2 possess 2D transport characteristics. The appearance of Mott's 2D law could originate from a potential disorder introduced by Mg substitution for Ti in S-Ti-S slabs. Meanwhile, the significant enhancement of absolute thermopower of Mg x Ti 1−x S 2 ͑x Ͼ 0͒ in the whole temperature range investigated could also be attributed to the reduction of electronic concentration after doping. The thermoelectric figure of merit ZT of heavily substituted compounds ͑x = 0.10 and 0.15͒ was smaller than that of TiS 2 , owing to the large increase of both their electrical resistivity and ͑lattice͒ thermal conductivity presumably caused by the reduced electron concentration and increased acoustic velocity, respectively. Nevertheless, ZT of the lightly substituted compound Mg 0.04 Ti 0.96 S 2 enhanced substantially due to the remarkable increase in its thermopower, and specifically it is ϳ1.6 times as great as that of TiS 2 at 300 K, indicating that doping ͑substitution͒ is an effective approach to enhance thermoelectric performance of TiS 2 .

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“…Because the TiS 2 layer is weakly stacked through van der Waals forces, the excess Ti atoms occupy the space between TiS 2 layers. The lattice parameter a monotonically increases from 0.3405 nm for Ti 1.001 S 2 to 0.3412 nm for Ti 1.093 S 2 , and c increases from 0.5691 nm for Ti 1.001 S 2 to 0.5711 nm for Ti 1.093 S 2 [70]. …”

Section: Tis2-based Layered Sulfidesmentioning

confidence: 99%

Hierarchical Architecturing for Layered Thermoelectric Sulfides and Chalcogenides

Jood

Ohta

2015

Materials

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Sulfides are promising candidates for environment-friendly and cost-effective thermoelectric materials. In this article, we review the recent progress in all-length-scale hierarchical architecturing for sulfides and chalcogenides, highlighting the key strategies used to enhance their thermoelectric performance. We primarily focus on TiS2-based layered sulfides, misfit layered sulfides, homologous chalcogenides, accordion-like layered Sn chalcogenides, and thermoelectric minerals. CS2 sulfurization is an appropriate method for preparing sulfide thermoelectric materials. At the atomic scale, the intercalation of guest atoms/layers into host crystal layers, crystal-structural evolution enabled by the homologous series, and low-energy atomic vibration effectively scatter phonons, resulting in a reduced lattice thermal conductivity. At the nanoscale, stacking faults further reduce the lattice thermal conductivity. At the microscale, the highly oriented microtexture allows high carrier mobility in the in-plane direction, leading to a high thermoelectric power factor.

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Electronic specific heat of Ti1+xS2 (0 < x < 0.1)

Cited by 15 publications

References 3 publications

Thermoelectric Properties of Co-Doped TiS2

Thermoelectric Properties of Co-Doped TiS2

The effect of Mg substitution for Ti on transport and thermoelectric properties of TiS2

Hierarchical Architecturing for Layered Thermoelectric Sulfides and Chalcogenides

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