Iron(II) selenide

Iron(II) selenide refers to a number of inorganic compounds of ferrous iron and selenide (Se2−). The phase diagram of the system Fe–Se[1] reveals the existence of several non-stoichiometric phases between ~49 at. % Se and ~53 at. % Fe, and temperatures up to ~450 °C. The low temperature stable phases are the tetragonal PbO-structure (P4/nmm) β-Fe1−xSe and α-Fe7Se8. The high temperature phase is the hexagonal, NiAs structure (P63/mmc) δ-Fe1−xSe. Iron(II) selenide occurs naturally as the NiAs-structure mineral achavalite.

Iron(II) selenide
Names
IUPAC name
Iron(II) selenide
Identifiers
3D model (JSmol)
ECHA InfoCard 100.013.798
EC Number
  • 215-177-1
UNII
Properties
FeSe
Molar mass 134.807 g/mol
Appearance black crystals
Density 4.72 g/cm3
Melting point 965 °C (1,769 °F; 1,238 K)
0.975 mg/100mL
Structure
hexagonal / tetragonal
Hazards
Main hazards toxic
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

More selenium rich iron selenide phases are the γ phases (γ and γˈ), assigned the Fe3Se4 stoichiometry, and FeSe2, which occurs as the marcasite-structure natural mineral ferroselite, or the rare pyrite-structure mineral dzharkenite.

It is used in electrical semiconductors.

Superconductivity

β-FeSe is the simplest iron-based superconductor but with diverse properties.[2] It starts to superconduct at 8 K at normal pressure[3] but its critical temperature (Tc) is dramatically increased to 38 K under pressure[4] and by means of intercalation. The combination of both intercalation and pressure results in re-emerging superconductivity at 48 K.[2]

In 2013 it was reported that a single atomic layer of FeSe epitaxially grown on SrTiO3 is superconductive with a then-record transition temperature for iron-based superconductors of 70 K.[5] This discovery has attracted significant attention and in 2014 a superconducting transition temperature of over 100K was reported for this system.[6]

It has been suggested that alternating layers of FeSe and CoSe (cobalt selenide) might boost Tc even further due to proximity effects. Cobalt has been used in other pnictogen compounds as a substitute for iron and found to work as well.

References
  1. Okamoto H (1991). "The Fe–Se (Iron-Selenium) System". Journal of Phase Equilibria. 12 (3): 383–389. doi:10.1007/BF02649932. S2CID 99966041.
  2. Yu. V. Pustovit; A. A. Kordyuk (2016). "Metamorphoses of electronic structure of FeSe-based superconductors (Review article)". Low Temp. Phys. 42 (11): 995. arXiv:1608.07751. Bibcode:2016LTP....42..995P. doi:10.1063/1.4969896. S2CID 119184569.
  3. F.-C. Hsu; et al. (2008). "Superconductivity in the PbO-type structure α-FeSe". Proc. Natl. Acad. Sci. USA. 105 (38): 14262–14264. arXiv:0807.2369. Bibcode:2008PNAS..10514262H. doi:10.1073/pnas.0807325105. PMC 2531064. PMID 18776050.
  4. Medvedev, S.; McQueen, T. M.; Troyan, I. A.; Palasyuk, T.; Eremets, M. I.; Cava, R. J.; Naghavi, S.; Casper, F.; Ksenofontov, V.; Wortmann, G.; Felser, C. (2009). "Electronic and Magnetic Phase Diagram of β-Fe1.01Se with superconductivity at 36.7 K under pressure". Nature Materials. 8 (8): 630–633. arXiv:0903.2143. Bibcode:2009NatMa...8..630M. doi:10.1038/nmat2491. PMID 19525948.
  5. R. Peng; et al. (2014). "Enhanced superconductivity and evidence for novel pairing in single-layer FeSe on SrTiO3 thin film under large tensile strain". Physical Review Letters. 112 (10): 107001. arXiv:1310.3060. Bibcode:2014PhRvL.112j7001P. doi:10.1103/PhysRevLett.112.107001. PMID 24679321.
  6. J.-F. Ge; et al. (2014). "Superconductivity in single-layer films of FeSe with a transition temperature above 100 K". Nature Materials. 14 (3): 285–9. arXiv:1406.3435. Bibcode:2015NatMa..14..285G. doi:10.1038/nmat4153. PMID 25419814.


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