Silver(I) selenide

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Silver(I) selenide
Silver(I) selenide
Names
IUPAC name
Silver(I) selenide
Other names
Naumannite

Argentous selenide
Identifiers
3D model (
JSmol
)
ECHA InfoCard
 100.013.727 Edit this at Wikidata
UNII
  • InChI=1S/2Ag.Se
    Key: GNWCVDGUVZRYLC-UHFFFAOYSA-N
  • [Se].[Ag].[Ag]
Properties
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)
insoluble
Band gap 0.15 eV [1]
Structure
orthorhombic, oP12
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).
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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.

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

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. ISBN 978-3-540-40488-0
    .
  2. ^ http://nevada-outback-gems.com/Reference_pages/sulfide_ores.htm Notes on naumannite.
  3. ISBN 978-1-4786-0887-5
    .
  4. S2CID 9316728
    .
  5. ISSN 1567-1739
    .
  6. ^
    S2CID 235698416
    .
  7. PMID 24295334
    .
  8. PMID 22540121
    .
  9. doi:10.1021/cm502317g
    .


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