Group IB 11 . Copper, Silver, Gold

Cuprous chalcogenides, CU2X, are basically dimorphic. The low-chalcocite CU2S (an important and widely distributed ore mineral of copper) has a structure 

Cupric sulfide, CuS, occurring as the mineral covellite (also known as covelline), exhibits a very unusual structure, in which the Cu is again partly 3-coordinate and partly 4-coordinate, with two-thirds of the sulfur atoms existing as S2 groups like those in pyrites. The low-temperature form of CuSe has also a covellite structure, the high-temperature modification (P-CuSe) being orthorhombic. All CuX2 compounds assume pyrite-type structures. 

Chalcopyrite or copper pyrite, CuFeS2, is one of the major ores of copper, estimated to account for about 50% of all the element s deposits. Compounds of the chalcopyrite type of the general formula ABC2 (with A = Cu, Ag B = Al, Ga, In  

Extensive structural, optical, and electronic studies on the chalcopyrite semiconductors have been stimulated by the promising photovoltaic and photoelectrochem-ical properties of the copper-indium diselenide, CuInSe2, having a direct gap of about 1.0 eV, viz. close to optimal for terrestrial photovoltaics, and a high absorption coefficient which exceeds 10 cm . The physical properties of this and the other compounds of the family can be modulated to some extent by a slight deviation from stoichiometry. Thus, both anion and cation deficiencies may be tolerated, inducing, respectively, n- and p-type conductivities a p-type behavior would associate to either selenium excess or copper deficiency. 

Gold(I) sulfide, AU2S gold(III) sulfide, AU2S3 gold(ni) selenide, Au2Se3. 

---