Silver(I) selenide

Silver selenide (Ag₂Se) 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 (Se²⁻) anion combining with the silver in the toning process.

Silver(I) selenide

Silver(I) selenide
Names
IUPAC name Silver(I) selenide
Other names Naumannite Argentous selenide
Identifiers
CAS Number	1302-09-6 Y
3D model (JSmol)	Interactive image
ECHA InfoCard	100.013.727
PubChem CID	6914520
UNII	QZ0B90W7EQ Y
CompTox Dashboard (EPA)	DTXSID2061644
InChI InChI=1S/2Ag.Se Key: GNWCVDGUVZRYLC-UHFFFAOYSA-N
SMILES [Se].[Ag].[Ag]
Properties
Chemical formula	Ag2Se
Molar mass	294.7 g/mol
Density	8.216 g/cm3, solid
Melting point	896.85 °C (1,646.33 °F; 1,170.00 K)
Solubility in water	insoluble
Band gap	0.15 eV [1]
Structure
Crystal structure	orthorhombic, oP12
Space group	P212121, No. 19
Thermochemistry
Enthalpy of fusion (ΔfH⦵fus)	56.9 J/g
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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-sulfur silver ores from mines in Nevada and Idaho.^[2][3]

Structure

Silver selenide has two crystal phases on the bulk phase diagram. At lower temperatures, it has an orthorhombic structure, β-Ag₂Se. This orthorhombic phase, stable at room temperature, is a narrow-gap semiconductor, with space group P2₁2₁2₁. The exact size of the band gap has been given variously from 0.02 eV to 0.22 eV.^[4]

There is also a high temperature cubic phase, α-Ag₂Se.,^[5] which it transforms into at temperatures above 130 °C. This high temperature phase has space group Im3m, No. 229, Pearson symbol cI20. The phase transition increases ionic conductivity by 10,000 times to about 2 S/cm.

A third metastable phase with a monoclinic structure and space group P2₁/n is known to form for colloidal Ag₂Se nanocrystals.^[6] The crystal structure of this polymorph is highly related to the acanthite phase of silver sulfide. For Ag₂Se, this polymorph is increasingly unstable for larger crystallites, which explains its absence on the bulk phase diagram.^[7] It is thought that the influence of the surface energy plays a role stabilizing this phase on the nanoscale, thus allowing its experimental isolation. Electronic structure calculations for this polymorph of Ag₂Se suggest that it is a narrow-gap semiconductor,^[6] which is supported by experimental evidence as well.^[8] Prior to 2021, the crystal structure of this polymorph was unknown, and this material was informally referred to as a "tetragonal" or "pseudo-tetragonal" polymorph of Ag₂Se.^[9] This terminology, while not technically correct, is prevalent in the literature pertaining to this metastable phase of Ag₂Se.

References

1. O. Madelung (2004). Semiconductors: data handbook. Birkhäuser. p. 461. ISBN 978-3-540-40488-0.
2. http://nevada-outback-gems.com/Reference_pages/sulfide_ores.htm Notes on naumannite.
3. Guilbert, John M.; Park Jr, Charles F. (2007-02-09). The Geology of Ore Deposits. Waveland Press. p. 557. ISBN 978-1-4786-0887-5.
4. 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 (1): 190–202. arXiv:mtrl-th/9602001. Bibcode:1996PhRvB..54..190K. doi:10.1103/PhysRevB.54.190. PMID 9984246. S2CID 9316728.
5. An, Boo Hyun; Ji, Hye Min; Wu, Jun-Hua; Cho, Moon Kyu; Yang, Ki-Yeon; Lee, Heon; Kim, Young Keun (2009). "Phase changeable silver selenide thin films fabricated by pulse electrodeposition". Current Applied Physics. 9 (6): 1338–1340. Bibcode:2009CAP.....9.1338A. doi:10.1016/j.cap.2008.12.017. ISSN 1567-1739.
6. Tappan, Bryce A.; Zhu, Bonan; Cottingham, Patrick; Mecklenburg, Matthew; Scanlon, David O.; Brutchey, Richard L. (2021). "Crystal Structure of Colloidally Prepared Metastable Ag2Se Nanocrystals". Nano Letters. 21 (13): 5881–5887. Bibcode:2021NanoL..21.5881T. doi:10.1021/acs.nanolett.1c02045. PMID 34196567. S2CID 235698416.
7. Sahu, Ayaskanta; Braga, Daniele; Waser, Oliver; Kang, Moon Sung; Deng, Donna; Norris, David J. (2014). "Solid-Phase Flexibility in Ag2Se Semiconductor Nanocrystals". Nano Letters. 14 (1): 115–121. Bibcode:2014NanoL..14..115S. doi:10.1021/nl4041498. PMID 24295334.
8. Sahu, Ayaskanta; Khare, Ankur; Deng, Donna D.; Norris, David J. (2012). "Quantum confinement in silver selenide semiconductor nanocrystals". Chemical Communications. 48 (44): 5458–5460. doi:10.1039/C2CC30539A. PMID 22540121.
9. Wang, Junli; Fan, Weiling; Yang, Juan; Da, Zulin; Yang, Xiaofei; Chen, Kangmin; Yu, Huan; Cheng, Xiaonong (2014). "Tetragonal–Orthorhombic–Cubic Phase Transitions in Ag2Se Nanocrystals". Chemistry of Materials. 26 (19): 5647–5653. doi:10.1021/cm502317g.