Copper(I) sulfide explained

Copper(I) sulfide is a copper sulfide, a chemical compound of copper and sulfur. It has the chemical compound Cu2S. It is found in nature as the mineral chalcocite. It has a narrow range of stoichiometry ranging from Cu1.997S to Cu2.000S.[1] Samples are typically black.

Preparation and reactions

Cu2S can be prepared by treating copper with sulfur or H2S. The rate depends on the particle size and temperature.[2] Cu2S reacts with oxygen to form SO2:[3]

The production of copper from chalcocite is a typical process in extracting the metal from ores. Usually, the conversion involves roasting, to give Cu2O and sulfur dioxide:[3]

Cuprous oxide readily converts to copper metal upon heating.

Structure

Stoichiometric

Two forms (a dimorphism) of Cu2S are known. The so-called low temperature monoclinic form ("low-chalcocite") has a complex structure with 96 copper atoms in the unit cell.[4] The hexagonal form, stable above 104 °C,[5] has 24 crystallographically distinct Cu atoms. Its structure has been described as approximating to a hexagonal close packed array of sulfur atoms with Cu atoms in planar 3 coordination. This structure was initially assigned an orthorhombic cell due to the twinning of the sample crystal.

Non-stoichiometric

As illustrated by the mineral djurleite, a cuprous sulfide is also known. With the approximate formula Cu1.96S, this material is non-stoichiometric (range Cu1.934S-Cu1.965S) and has a monoclinic structure with 248 copper and 128 sulfur atoms in the unit cell.[4] Cu2S and Cu1.96S are similar in appearance and hard to distinguish one from another.[6]

Phase transition

The electrical resistivity increases abruptly at the phase transition point around 104 °C, with the precise temperature depending on the stoichiometry.[7] [8]

See also

Notes and References

  1. An electrochemical investigation of the system copper-sulfur. Potter, R. W. . Economic Geology. 1977. 72 . 8. 1524–1542. 10.2113/gsecongeo.72.8.1524. 1977EcGeo..72.1524P .
  2. The formation of Cu2S from the elements I. Copper used in form of powders. Blachnik R., Müller A.. 10.1016/S0040-6031(00)00545-1. 2000. Thermochimica Acta. 361. 31.
  3. Wiberg, Egon and Holleman, Arnold Frederick (2001) Inorganic Chemistry, Elsevier
  4. 10.1126/science.203.4378.356. Djurleite (Cu1.94S) and Low Chalcocite (Cu2S): New Crystal Structure Studies. 1979. Evans. H. T.. Science. 203. 4378. 356–8. 17772445. 1979Sci...203..356E . 6132717 .
  5. Wells A.F. (1984) Structural Inorganic Chemistry, 5th ed., Oxford Science Publications,
  6. Copper coordination in low chalcocite and djurleite and other copper-rich sulfides. Evans H.T.. American Mineralogist. 1981. 66. 7–8. 807–818.
  7. Garisto . Dan . 2023-08-16 . LK-99 isn't a superconductor — how science sleuths solved the mystery . Nature . 620 . 7975 . 705–706 . en . 10.1038/d41586-023-02585-7. 37587284 . 2023Natur.620..705G . 260955242 .
  8. Jain, Prashant K. "Phase transition of copper (I) sulfide and its implication for purported superconductivity of LK-99." arXiv preprint arXiv:2308.05222 (2023).