Copper sulfides band structures

The copper, copper-iron, and the silver sulfides are more complex than the sulfides discussed previously, containing several cations or cation sites in their structures. Thus chalcopyrite (CuFeSj), although having a fairly simple structure based on that of sphalerite, but with Cu and Fe alternately replacing Zn atoms, contains both Cu+ and Fe + in regular tetrahedral coordination (as indicated by neutron diffraction and Moss-bauer studies see Vaughan and Craig, 1978). A family of more than thirty synthetic compounds with the chalcopyrite structure is known, and their properties have been studied because of potential applications as semiconductors. Miller et al. (1981) have reviewed the crystal structures, vibrational properties, and band structures of these materials. 

In the extreme class III behaviour,360-362 two types of structures were envisaged clusters and infinite lattices (Table 17). The latter, class IIIB behaviour, has been known for a number of years in the nonstoichiometric sulfides of copper (see ref. 10, p. 1142), and particularly in the double layer structure of K[Cu4S3],382 which exhibits the electrical conductivity and the reflectivity typical of a metal. The former, class IIIA behaviour, was looked for in the polynuclear clusters of copper(I) Cu gX, species, especially where X = sulfur, but no mixed valence copper(I)/(II) clusters with class IIIA behaviour have been identified to date. Mixed valence copper(I)/(II) complexes of class II behaviour (Table 17) have properties intermediate between those of class I and class III. The local copper(I)/(II) stereochemistry is well defined and the same for all Cu atoms present, and the single odd electron is associated with both Cu atoms, i.e. delocalized between them, but will have a normal spin-only magnetic moment. The complexes will be semiconductors and the d-d spectra of the odd electron will involve a near normal copper(II)-type spectrum (see Section 53.4.4.5), but in addition a unique band may be observed associated with an intervalence CuVCu11 charge transfer band (IVTC) (Table 19). While these requirements are fairly clear,360,362 their realization for specific systems is not so clearly established. 

---