Silver(I) selenide

Silver(I) selenide
Other names Naumannite
Identifiers
CAS number	1302-09-6
Properties
Molecular formula	Ag2Se
Molar mass	294.7 g/mol
Density	8.216 g/cm3, solid
Melting point	880 °C
Band gap	0.15 eV [1]
Structure
Crystal structure	orthorhombic, oP12
Space group	P212121, No. 19
Y selenide (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Silver selenide (Ag₂Se) is a clear, hexagonal compound. It is the reaction product formed when selenium toning analog silver gelatine photo papers in photographic print toning. The selenium toner contains sodium selenite (Na₂SeO₃) as one of its active ingredients, which is the source of the selenide (Se^2-) anion combining with the silver in the toning process.

It is found in nature as the mineral naumannite, a comparatively rare silver mineral which has nevertheless become recognized as important silver compound in some low-sulfer silver ores from mines in Nevada.^[2]

Structure

Silver selenide normally exists in the orthorhombic β phase but at temperatures above 130 °C transforms into the cubic α-Ag₂Se (Space group Im-3m, No. 229, Pearson symbol cI20). The phase transition increases ionic conductivity by 10,000 times to about 2 S/cm ^[3]

References

1. ^ O. Madelung (2004). Semiconductors: data handbook. Birkhäuser. p. 461. ISBN 3540404880. http://books.google.com/books?id=v_8sMfNAcA4C&pg=PA461. 
2. ^ http://nevada-outback-gems.com/Reference_pages/sulfide_ores.htm Notes on naumannite.
3. ^ Kirchhoff F., Holender J.M., Gillan M.J. (1996). "Structure, dynamics, and electronic structure of liquid Ag-Se alloys investigated by ab initio simulation". Physical Review B 54: 190–202. doi:10.1103/PhysRevB.54.190.