Tantalum(IV) sulfide

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Tantalum(IV) sulfide
Molybdenite-3D-balls.png
Crystal structure showing two stacked S-Ta-S sheets
Names
Other names
tantalum disulfide
Identifiers
3D model (JSmol)
ECHA InfoCard 100.032.047
Properties
TaS2
Molar mass 245.078 g/mol[1]
Appearance black crystals[1]
Density 6.86 g/cm3[1]
Melting point >3000 °C [1]
Insoluble[1]
Hazards
not listed
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Tantalum(IV) sulfide is the inorganic compound with the formula TaS2. It is a layered compound with three-coordinate sulfide centres and trigonal prismatic metal centres. It is structurally similar to the more famous material molybdenum disulfide, MoS2. TaS2 is a semiconductor with d1 electron configuration. Although an obscure material otherwise, TaS2 has been the subject of numerous studies because it is a versatile host for intercalation of electron donors,[2] and because it exhibits unusual phase transitions at low temperatures.

Preparation[edit]

TaS2 is prepared by reaction of powdered tantalum and sulfur at ~900 °C.[3] It is purified and crystallized by chemical vapor transport using iodine as the transporting agent:[4]

TaS2 + 2 I2 ⇌ TaI4 + 2 S

Properties[edit]

(a): Schematic of the David star pattern in 1T-TaS2 where green atoms are S and purple are Ta. (b) and (c) are STM images taken at 6.5 K at different magnifications, before and after application of 2.8 V pulses through the STM tip. Insets show ~10 times magnified images.
The mosaic state in 1T-TaS2 observed by STM at 6.5 and 45 K (right).

Three major crystalline phases are known for TaS2: trigonal 1T with one S-Ta-S sheet per unit cell, hexagonal 2H with two S-Ta-S sheets, and rhombohedral 3R with three S-Ta-S sheets per cell; 4H and 6R phases are also observed, but less frequently. These polymorphs mostly differ by the relative arrangement of the S-Ta-S sheet rather than the sheet structure.[5]

2H-TaS2 is a superconductor with the bulk transition temperature TC = 0.5, which increases to 2.2 K in flakes with a thickness of a few atomic layers.[3] The bulk TC value increases up to ~8 K at 10 GPa and then saturates with increasing pressure.[6] In contrast, 1T-TaS2 starts superconducting only at ~2 GPa; as a function of pressure its TC quickly rises up to 5 K at ~4 GPa and then saturates.[7]

At ambient pressure and low temperatures 1T-TaS2 is a Mott insulator. Upon heating it abruptly changes to a nearly commensurate charge density wave (NCCDW) state at TNCCDW ~ 190 K, to an incommensurate CDW (ICCDW) state at TICCDW ~ 350 K, and to a metallic state at TM ~ 550 K, as revealed by electrical conductivity measurements.[7] The NCCDW transitions exhibits a strong thermal hysteresis, and occurs at ~ 150 K upon cooling and at ~ 220 K upon heating; both these temperatures depend on the heating/cooling rate. As a function of sample thickness t the NCCDW transition suddenly disappears at t < 35 nm. It can also be suppressed in thicker samples by application of a gate voltage (~3 V) in a planar transistor configuration. Meanwhile, the ICCDW and metallic transitions exhibit a much smaller thermal hysteresis and much weaker dependences on the heating/cooling rate, sample thickness and applied voltage.[8]

In the CDW state the TaS2 lattice deforms to create a periodic Star of David pattern. Application of voltage pulses (~2–3 V) in a scanning tunneling microscope (STM) to the CDW state creates a "mosaic state" consisting of nanometer-sized domains, where both the domains and their walls exhibit metallic conductivity. This mosaic structure is metastable and gradually disappears upon heating from ~5 to 50 K.[4][9]

Similar to other layered materials, TaS2 can be exfoliated into flakes containing one or more S-Ta-S sheets using the Scotch tape technique.[10]

References[edit]

  1. ^ a b c d e Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.93. ISBN 1439855110. 
  2. ^ Revelli, J. F.; Disalvo, F. J. (1995). "Tantalum Disulfide (TaS2) and Its Intercalation Compounds". Inorganic Syntheses. Inorganic Syntheses. 30. p. 155. ISBN 9780470132616. doi:10.1002/9780470132616.ch32. 
  3. ^ a b Navarro-Moratalla, Efrén; Island, Joshua O.; Mañas-Valero, Samuel; Pinilla-Cienfuegos, Elena; Castellanos-Gomez, Andres; Quereda, Jorge; Rubio-Bollinger, Gabino; Chirolli, Luca; Silva-Guillén, Jose Angel; Agraït, Nicolás; Steele, Gary A.; Guinea, Francisco; Van Der Zant, Herre S. J.; Coronado, Eugenio (2016). "Enhanced superconductivity in atomically thin TaS2". Nature Communications. 7: 11043. PMID 26984768. doi:10.1038/ncomms11043. 
  4. ^ a b Cho, Doohee; Cheon, Sangmo; Kim, Ki-Seok; Lee, Sung-Hoon; Cho, Yong-Heum; Cheong, Sang-Wook; Yeom, Han Woong (2016). "Nanoscale manipulation of the Mott insulating state coupled to charge order in 1T-TaS2". Nature Communications. 7: 10453. PMC 4735893Freely accessible. PMID 26795073. doi:10.1038/ncomms10453. 
  5. ^ Dunnill, Charles W.; MacLaren, Ian; Gregory, Duncan H. (2010). "Superconducting tantalum disulfide nanotapes; growth, structure and stoichiometry". Nanoscale. 2 (1): 90–7. PMID 20648369. doi:10.1039/B9NR00224C. 
  6. ^ Freitas, D. C.; Rodière, P.; Osorio, M. R.; Navarro-Moratalla, E.; Nemes, N. M.; Tissen, V. G.; Cario, L.; Coronado, E.; García-Hernández, M.; Vieira, S.; Núñez-Regueiro, M.; Suderow, H. (2016). "Strong enhancement of superconductivity at high pressures within the charge-density-wave states of 2H−TaS2 and 2H−TaSe2". Physical Review B. 93 (18). doi:10.1103/PhysRevB.93.184512. 
  7. ^ a b Sipos, B.; Kusmartseva, A. F.; Akrap, A.; Berger, H.; Forró, L.; Tutiš, E. (2008). "From Mott state to superconductivity in 1T-TaS2". Nature Materials. 7 (12): 960. PMID 18997775. doi:10.1038/nmat2318. 
  8. ^ Yoshida, Masaro; Zhang, Yijin; Ye, Jianting; Suzuki, Ryuji; Imai, Yasuhiko; Kimura, Shigeru; Fujiwara, Akihiko; Iwasa, Yoshihiro (2014). "Controlling charge-density-wave states in nano-thick crystals of 1T-TaS2". Scientific Reports. 4: 7302. PMC 4252899Freely accessible. PMID 25466764. doi:10.1038/srep07302. 
  9. ^ Ma, Liguo; Ye, Cun; Yu, Yijun; Lu, Xiu Fang; Niu, Xiaohai; Kim, Sejoong; Feng, Donglai; Tománek, David; Son, Young-Woo; Chen, Xian Hui; Zhang, Yuanbo (2016). "A metallic mosaic phase and the origin of Mott-insulating state in 1T-TaS2". Nature Communications. 7: 10956. PMC 4792954Freely accessible. PMID 26961788. doi:10.1038/ncomms10956. 
  10. ^ Sakabe, Daiki; Liu, Zheng; Suenaga, Kazutomo; Nakatsugawa, Keiji; Tanda, Satoshi (2017). "Direct observation of mono-layer, bi-layer, and tri-layer charge density waves in 1T-TaS2 by transmission electron microscopy without a substrate". Npj Quantum Materials. 2. doi:10.1038/s41535-017-0025-8.