On the Structural Properties of the Ta(1+x)Se2 Phase.

Bjerkelund, Einar; Kjekshus, Arne; Nilsson, Åke; Sandström, Jan; Theorell, Hugo; Blinc, R.; Paušak, S.; Ehrenberg, L.; Dumanović, J.

doi:10.3891/acta.chem.scand.21-0513

Cited by 76 publications

(48 citation statements)

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“…Then this material was heated in the presence of I 2 within a sealed ampule with a 100 °C temperature gradient; these "chemical vapor transport" conditions [24] resulted in clusters of metallic gray crystals. As shown in Figure 1 Figure 1c, the experimental diffraction pattern matches literature data for 2H-TaSe 2 very well [25,26]. In addition, we observe traces of 3R-TaSe 2 , in line with common observations of polytype mixtures within TaSe systems [20,23].…”

Section: Materials Synthesis and Sample Preparationsupporting

confidence: 73%

Phonon and thermal properties of exfoliated TaSe2 thin films

Yan

Jiang

Pope

et al. 2013

Journal of Applied Physics

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We report on the phonon and thermal properties of thin films of tantalum diselenide (2H-TaSe 2 ) obtained via the "graphene-like" mechanical exfoliation of crystals grown by chemical vapor transport. The ratio of the intensities of the Raman peak from the Si substrate and the E 2g peak of TaSe 2 presents a convenient metric for quantifying film thickness. The temperature coefficients for two main Raman peaks, A 1g and E 2g , are -0.013 and -0.0097 cm -1 / o C, respectively. The Raman optothermal measurements indicate that the room temperature thermal conductivity in these films decreases from its bulk value of ~16 W/mK to ~9 W/mK in 45-nm thick films. The measurement of electrical resistivity of the field-effect devices with TaSe 2 channels indicates that heat conduction is dominated by acoustic phonons in these van der Waals films. The scaling of thermal conductivity with the film thickness suggests that the phonon scattering from the film boundaries is substantial despite the sharp interfaces of the mechanically cleaved samples. These results are important for understanding the thermal properties of thin films exfoliated from TaSe 2 and other metal dichalcogenides, as well as for evaluating self-heating effects in devices made from such materials.KEYWORDS: van der Waals materials, tantalum diselenide, Raman spectroscopy, thermal conductivity, metal dichalcogenide, thin film *Corresponding authors: salguero@uga.edu (TTS) and balandin@ee.ucr.edu (AAB) 2 | P a g e

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Section: Materials Synthesis and Sample Preparationsupporting

confidence: 73%

Phonon and thermal properties of exfoliated TaSe2 thin films

Yan

Jiang

Pope

et al. 2013

Journal of Applied Physics

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“…1A), Ta is found in trigonal prismatic coordination in Se-Ta-Se layers that are stacked along the c axis of the hexagonal (or rhombohedral) cell. The 2H and 3R polytypes differ only in their stacking periodicity-the structure repeats after two layers in the 2H form and three layers in the 3R form (20)(21)(22). The 3R form can be synthesized, but it is not the stable variant (the 2H form is) and so has been the subject of little study.…”

mentioning

confidence: 99%

Polytypism, polymorphism, and superconductivity in TaSe ₂ _−x Te _x

Luo¹,

Xie²,

Tao

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

105

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Polymorphism in materials often leads to significantly different physical properties-the rutile and anatase polymorphs of TiO 2 are a prime example. Polytypism is a special type of polymorphism, occurring in layered materials when the geometry of a repeating structural layer is maintained but the layer-stacking sequence of the overall crystal structure can be varied; SiC is an example of a material with many polytypes. Although polymorphs can have radically different physical properties, it is much rarer for polytypism to impact physical properties in a dramatic fashion. Here we study the effects of polytypism and polymorphism on the superconductivity of TaSe 2 , one of the archetypal members of the large family of layered dichalcogenides. We show that it is possible to access two stable polytypes and two stable polymorphs in the TaSe 2−x Te x solid solution and find that the 3R polytype shows a superconducting transition temperature that is between 6 and 17 times higher than that of the much more commonly found 2H polytype. The reason for this dramatic change is not apparent, but we propose that it arises either from a remarkable dependence of T c on subtle differences in the characteristics of the single layers present or from a surprising effect of the layer-stacking sequence on electronic properties that are typically expected to be dominated by the properties of a single layer in materials of this kind.he MX 2 layered transition-metal dichalcogenides (TMDCs, M = Mo, W, V, Nb, Ta, Ti, Zr, Hf, or Re and X = Se, S, or Te), have long been of interest due to the rich electronic properties that emerge due to their low dimensionality (1-9). Structurally, these compounds can be regarded as having strongly bonded (2D) X-M-X layers, with M in either trigonal prismatic or octahedral coordination with X, and weak interlayer X-X bonding of the van der Waals type. Many of these materials manifest charge-density waves and competition between chargedensity waves (CDWs) and superconductivity, e.g., refs. 5-9. Among the TMDCs, the 2H (H: hexagonal) polytype of tantalum diselenide (2H-TaSe 2 ) is considered one of the foundational materials (8-18), showing a transition from a metallic phase to an incommensurate charge-density wave (ICDW) phase at 123 K, followed by a "lock-in" transition to a commensurate chargedensity wave (CCDW) phase at 90 K. It finally becomes a superconductor with a rather low transition temperature

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“…[39][40] All Bragg reflections of crystal B could be indexed on a lattice with a = 3.439 (2) Å and c = 12.870 (2) Å. Superlattice reflections were not observed. Structure solution using superflip [36] has given the positions of Ta and Se.…”

Section: Crystal Structure Of Crystal B Of Batch IImentioning

confidence: 99%

“…They are equal to the positions reported for 2H-TaSe 2 of NbS 2 structure type. [39,40] Intercalated copper and additional tantalum atoms are at partially occupied octahedral sites in the van der Waals gaps. The best fit to the diffraction data was obtained by lowering the symmetry to P3m1 [R F (obs) = 0.0578, wR F (obs) = 0.0651, GoF (all) = 3.81].…”

Section: Crystal Structure Of Crystal B Of Batch IImentioning

confidence: 99%

Synthesis, Superstructure, and Vacancy‐Ordering in 2H‐Cu_xTa_1+ySe₂ (x, y = 0.52, 0 and 0.16, 0.08)

Ali

Mondal

Smaalen

2014

Zeitschrift anorg allge chemie

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Abstract. Single crystals of Cu x Ta 1+y Se 2 were grown by chemical vapor transport. Single crystals of different compositions were obtained at slightly different reaction conditions from mixtures of the reactants of the same nominal composition. It is suggested that different diameters of the ampoules imply different contributions of convection and diffusion to the mass transport, and thus are responsible for different ratios of the amount of Cu, Ta, and Se transported. 2H-Cu 0.52 TaSe 2 (x = 0.52, y = 0) is formed in the narrower ampoule (diameter 15 mm). The crystal structure is based on the MoS 2 type of stacking of TaSe 2 layers. Partial ordering of Cu over the tetrahedral

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On the Structural Properties of the Ta(1+x)Se2 Phase.

Cited by 76 publications

References 0 publications

Phonon and thermal properties of exfoliated TaSe2 thin films

Phonon and thermal properties of exfoliated TaSe2 thin films

Polytypism, polymorphism, and superconductivity in TaSe ₂ _−x Te _x

Synthesis, Superstructure, and Vacancy‐Ordering in 2H‐Cu_xTa_1+ySe₂ (x, y = 0.52, 0 and 0.16, 0.08)

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On the Structural Properties of the Ta(1+x)Se2 Phase.

Cited by 76 publications

References 0 publications

Phonon and thermal properties of exfoliated TaSe2 thin films

Phonon and thermal properties of exfoliated TaSe2 thin films

Polytypism, polymorphism, and superconductivity in TaSe 2 −x Te x

Synthesis, Superstructure, and Vacancy‐Ordering in 2H‐CuxTa1+ySe2 (x, y = 0.52, 0 and 0.16, 0.08)

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Polytypism, polymorphism, and superconductivity in TaSe ₂ _−x Te _x

Synthesis, Superstructure, and Vacancy‐Ordering in 2H‐Cu_xTa_1+ySe₂ (x, y = 0.52, 0 and 0.16, 0.08)