Copper sulfide is a family of compounds and minerals with the formula CuxSy. Both minerals and synthetic materials contain these compounds. Some copper sulfides are economically important ores.
The main copper sulfide minerals include Cu2S (chalcocite) and CuS (azurite). In the mining industry, the mineral bornite or chalcopyrite, consisting of mixed copper-iron sulfides, is often referred to as "copper sulfide". In chemistry, "binary copper sulfide" is any binary compound of the elements copper and sulfur. Regardless of its origin, the composition of copper sulfide varies widely, 0.5 ≤ Cu/S ≤ 2, including many non-stoichiometric copper ii sulfide compounds.
Copper sulfide can be divided into three categories:
Monosulfide, 1.6 ≤ Cu/S ≤ 2: its crystal structure consists of isolated sulfide anions closely related to hcp or fcc lattices, without any direct S-S bonds. Cu ions are distributed in a complex manner at interstitial sites with triangular and twisted tetrahedral coordination and are quite mobile. Therefore, this group of copper sulfides exhibits ionic conductivity at slightly elevated temperatures. In addition, most of its members are semiconductors.
Mixed monosulfide and disulfide compounds of copper contain both monosulfide (S2−) and disulfide (S2)n− anions. Their crystal structures generally consist of alternating hexagonal layers of monosulfide and disulfide anions with copper cations in the triangular and tetrahedral interstices. For example, CuS can be written as Cu3(S2)S. Several non-stoichiometric compounds with Cu:S ratios between 1.0 and 1.4 also contain monosulfide and disulfide ions. Depending on their composition, these copper sulfides are either semiconductors or metallic conductors.
At very high pressure, copper disulfide, CuS2, can be synthesized. Its crystal structure is similar to that of pyrite, with all sulfur atoms present as S-S units. Copper disulfide is a metallic conductor due to the incomplete occupation of the sulfur p-band. Different stoichiometric compositions can be obtained by changing the redox atmosphere of the synthesis environment.
