Iron(II) selenide

Iron(II) selenide

Names
IUPAC name Iron(II) selenide
Identifiers
CAS Number	1310-32-3
EC Number	215-177-1
Jmol 3D model	Interactive image
PubChem	14795
InChI InChI=1S/Fe.Se Key: WALCGGIJOOWJIN-UHFFFAOYSA-N
SMILES [Fe]=[Se]
Properties
Chemical formula	FeSe
Molar mass	134.81 g/mol
Appearance	black crystals
Density	4.72 g/cm3
Melting point	965 °C (1,769 °F; 1,238 K)
Solubility in water	0.975 g/100 mL
Structure
Crystal structure	hexagonal
Vapor pressure	{{{value}}}
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Iron(II) selenide refers to a number of inorganic compounds of ferrous iron and selenide (Se²⁻). The phase diagram of the system Fe–Se 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-Fe_1-xSe and α-Fe₇Se₈. The high temperature phase is the hexagonal, NiAs structure (P6₃/mmc) δ-Fe_1-xSe. Iron (II) selenide occurs naturally as the NiAs-structure mineral achavalite.

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 feroselite, or the rare pyrite-structure mineral dzharkenite.

It is used in electrical semiconductors.

Superconductivity

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 70K. This discovery has attracted significant attention and in 2014 a superconducting transition temperature of over 100K was reported for this system.

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.