Bismuth selenide

Bismuth selenide

Names
IUPAC name selenoxobismuth, selanylidenebismuth [1]
Identifiers
CAS Number	12068-69-8 Y
3D model (JSmol)	Interactive image
ChemSpider	145787
ECHA InfoCard	100.031.901
EC Number	235-104-7
PubChem CID	6379269
UNII	9I1Y040903
CompTox Dashboard (EPA)	DTXSID60893213
InChI InChI=1S/2Bi.3Se Key: OMEPJWROJCQMMU-UHFFFAOYSA-N
SMILES [Se-2].[Se-2].[Se-2].[Bi+3].[Bi+3]
Properties
Chemical formula	Bi2Se3
Molar mass	654.8 g/mol [2]
Appearance	Dull grey [3]
Density	6.82 g/cm3[2]
Melting point	710 °C (1,310 °F; 983 K)[2]
Solubility in water	insoluble
Solubility	insoluble in organic solvents soluble in strong acids [2]
Structure
Crystal structure	rhombohedral
Thermochemistry
Std enthalpy of formation (ΔfH⦵298)	-140 kJ/mol
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Toxic [3]
NFPA 704 (fire diamond)	2 0 0
Related compounds
Other anions	Bismuth(III) oxide Bismuth trisulfide Bismuth telluride
Other cations	Arsenic triselenide Antimony triselenide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Bismuth selenide (Bi₂Se₃) is a gray compound of bismuth and selenium also known as bismuth(III) selenide.

Properties

Bismuth selenide is a semiconductor and a thermoelectric material.^[4] While stoichiometric bismuth selenide should be a semiconductor with a gap of 0.3 eV, naturally occurring selenium vacancies act as electron donors, so Bi₂Se₃ is intrinsically n-type.^[5][6][7]

Bismuth selenide has a topologically insulating ground-state.^[8] Topologically protected Dirac cone surface states have been observed in Bismuth selenide and its insulating derivatives leading to intrinsic topological insulators,^{[6][9][10][11]} which later became the subject of world-wide scientific research.^{[12][13][14][15]}

Bismuth selenide is a van der Waals material consisting of covalently bound five-atom layers (quintuple layers) which are held together by van der Waals interactions^[16] and spin-orbit coupling effects.^[17] Although the (0001) surface is chemically inert (mostly due to the inert-pair effect of Bi^[17]), there are metallic surface states, protected by the non-trivial topology of the bulk. For this reason, the Bi₂Se₃ surface is an interesting candidate for van der Waals epitaxy and subject of scientific research. For instance, different phases of antimony layers can be grown on Bi₂Se₃,^[18][19] by means of which topological pn-junctions can be realised.^[20] More intriguingly, Sb layers undergo topological phase transitions when attached to the Bi₂Se₃ surface and thus inherit the non-trivial topological properties of the Bi₂Se₃ substrate.^[21][22]

Production

Although bismuth selenide occurs naturally (as the mineral guanajuatite) at the Santa Catarina Mine in Guanajuato, Mexico^[23] as well as some sites in the United States and Europe,^[24] such deposits are rare and contain a significant level of sulfur^[24] atoms as an impurity. For this reason, most bismuth selenide used in research into potential commercial applications is synthesized. Commercially-produced samples are available for use in research, but the concentration of selenium vacancies is heavily dependent upon growth conditions,^[25][26] and so bismuth selenide used for research is often synthesized in the laboratory.

A stoichiometric mixture of elemental bismuth and selenium, when heated above the melting points of these elements in the absence of air, will become a liquid that freezes to crystalline Bi₂Se₃.^[27] Large single crystals of bismuth selenide can be prepared by the Bridgman–Stockbarger method.^[28]

See also

• Thermoelectric materials
• Thermoelectric effect
• Topological insulators

References