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.

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.[7] Upon heating it changes to a Triclinic charge density wave (TCDW) state at TTCDW ~ 220 K[8][9][10], to a nearly commensurate charge density wave (NCCDW) state at TNCCDW ~ 280 K[11], to an incommensurate CDW (ICCDW) state at TICCDW ~ 350 K[11], and to a metallic state at TM ~ 600 K.

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][12]

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. doi:10.1002/9780470132616.ch32. ISBN 9780470132616. 
  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. Bibcode:2016NatCo...711043N. doi:10.1038/ncomms11043. PMC 5512558Freely accessible. PMID 26984768. 
  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. Bibcode:2016NatCo...710453C. doi:10.1038/ncomms10453. PMC 4735893Freely accessible. PMID 26795073. 
  5. ^ Dunnill, Charles W.; MacLaren, Ian; Gregory, Duncan H. (2010). "Superconducting tantalum disulfide nanotapes; growth, structure and stoichiometry". Nanoscale. 2 (1): 90–7. Bibcode:2010Nanos...2...90D. doi:10.1039/B9NR00224C. PMID 20648369. 
  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): 184512. Bibcode:2016PhRvB..93r4512F. 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. Bibcode:2008NatMa...7..960S. doi:10.1038/nmat2318. PMID 18997775. 
  8. ^ Tanda, Satoshi; Sambongi, Takashi; Tani, Toshiro; Tanaka, Shoji (1984). "X-Ray Study of Charge Density Wave Structure in 1T-TaS2". J. Phys. Soc. Jpn. 53: 476. doi:10.1143/JPSJ.53.476. 
  9. ^ Tanda, Satoshi; Sambongi, Takashi (1985). "X-ray study of the new charge-density-wave phase in 1T-TaS2". Synthetic Metals. 11: 85. doi:10.1016/0379-6779(85)90177-8. 
  10. ^ Coleman, R. V.; Giambattista, B.; Hansma, P.K; Johnson, A.; McNairy, W.W.; Slough, C.G. (1988). "Scanning tunnelling microscopy of charge-density waves in transition metal chalcogenides". Advances in Physics. 37: 559. doi:10.1080/00018738800101439. 
  11. ^ a b Wilson, J.A.; Di Salvo, F.J.; Mahajan, S. (1975). "Charge-density waves and superlattices in the metallic layered transition metal dichalcogenides". Advances in Physics. 24: 117. doi:10.1080/00018737500101391. 
  12. ^ 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. Bibcode:2016NatCo...710956M. doi:10.1038/ncomms10956. PMC 4792954Freely accessible. PMID 26961788.