Argyrodite
General
CategorySulfide mineral
Formula
(repeating unit)
Ag8GeS6
IMA symbolAgy[1]
Strunz classification2.BA.35
Crystal systemOrthorhombic
Crystal classPyramidal (mm2)
H-M symbol: (mm2)
Space groupPna21
Unit cella = 15.149, b = 7.476
c = 10.589 [Å]; Z = 4
Identification
ColorBlack, purplish tinge
Crystal habitPseudo-octahedra or pseudo-cubic, dodecahedra, cubes; radiating crystal aggregates, botryoidal crusts, or massive
TwinningPseudospinel law {111} penetration twins
CleavageAbsent
FractureUneven to conchoidal
Mohs scale hardness2.5
LusterMetallic
DiaphaneityOpaque
Specific gravity6.2-6.5
Optical propertiesWeakly anisotropic
PleochroismWeak
References[2][3]

Argyrodite is an uncommon silver germanium sulfide mineral with formula Ag8GeS6. The color is iron-black with a purplish tinge, and the luster metallic.

Discovered and named by Albin Weisbach in 1886,[4] it is of interest as it was the material from which Clemens Winkler isolated the element germanium, 15 years after it had been postulated by Mendeleev. It was first described for an occurrence in the Himmelsfürst Mine, Ore Mountains, Freiberg, Saxony, Germany.[3]

The Freiberg mineral had previously been imperfectly described by August Breithaupt under the name "Plusinglanz", and Bolivian crystals were incorrectly described in 1849 as crystallized brongniardite.[5]

Isomorphous with argyrodite is the corresponding tin bearing mineral Ag8SnS6, also found in Bolivia as pseudocubic crystals, and known by the name canfieldite.[5] There is also a related mineral, putzite, with composition (Cu4.7Ag3.3)GeS6.

Argyrodite gets its name from the Greek words that loosely translate into "rich in silver".[2]

Argyrodite-type material

The term argyrodite is also used for other materials with a similar crystal structure, in particular lithium based argyrodite-type materials, which have received interest from researchers as a potential solid-state electrolyte for lithium-ion batteries.[6][7]

They are considered to be of the form:

Li
7-x
BCh
6-x
X
x

With x between 0 and 1, B denoting either phosphor or arsenic, Ch for sulfur or selenium and X for chlorine, bromine or iodine.[6] However, other forms exist and can be grouped into three main categories, halogen-based argyrodites, halogen-based argyrodites doped with additional semi-metal or metal components and halogen-free argyrodites based on Li, P, S along with a semi-metal.[8]

References

  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. 1 2 Handbook of Mineralogy
  3. 1 2 Mindat.org
  4. Weisbach, Albin (1886). "Argyrodit, ein neues Silbererz". Neues Jahrbuch für Geologie und Paläontologie. 2: 67.
  5. 1 2 Spencer 1911, p. 488.
  6. 1 2 Raghavan, Prasanth; Fatima, Jabeen (2021-04-05). Ceramic and Specialty Electrolytes for Energy Storage Devices. CRC Press. ISBN 978-1-000-35180-4.
  7. Brinek, Marina; Hiebl, Caroline; Wilkening, H. Martin R. (2020-06-09). "Understanding the Origin of Enhanced Li-Ion Transport in Nanocrystalline Argyrodite-Type Li6PS5I". Chemistry of Materials. 32 (11): 4754–4766. doi:10.1021/acs.chemmater.0c01367. ISSN 0897-4756. PMC 7304077. PMID 32565618.
  8. Lu, Xin; Tsai, Chih-Long; Yu, Shicheng; He, Hongying; Camara, Osmane; Tempel, Hermann; Liu, Zigeng; Windmüller, Anna; Alekseev, Evgeny V.; Köcher, Simone; Basak, Shibabrata; Lu, Li; Eichel, Rüdiger A.; Kungl, Hans (2022). "Lithium phosphosulfide electrolytes for solid-state batteries: Part II". Functional Materials Letters. 15 (7n08): 2240002. doi:10.1142/S1793604722400021. ISSN 1793-6047.

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