Disordered chalcogenides

Tanaka K (2001) Chalcogenide Glasses. In Encyclopedia of Materials Science and Technology, Elsevier Science Ltd Oxford ISBN 0-08-0431526, pp. 1123-1131 Ovshinsky SR (1968) Reversible Electrical Switching Phenomena in Disordered Stmctures. Phys Rev Lett 21 1450-1453... 

The most familiar application of amorphous semiconductors will, for many readers, be in the field of replication of printed matter. The xerography process, npon which many modem photocopiers are based, involves the ability of an electrostatically charged plate of amorphous chalcogenide (or similar material) to discharge under illn-mination. Residual charging of illuminated areas is employed in the transfer of ink onto the duplicator paper. Naturally, the mobility of photoinduced carriers in the amorphons semiconductor photoreceptor is of central importance in the validity of the process, and considerable commercial effort has been (and is being) devoted to the study of transport in disordered materials suitable for the process. 

One of the properties of a class of materials known as chalcogenide glasses is that they exhibit a wide spectrum of photoinduced effects. Photoinduced phenomena have recently been extensively studied (see corresponding references in previous sections), partly as an interesting subject for fundamental research in the field of disordered sohds and partly due to the potential apphcation of these phenomena in opto(photo)electronics (xerography and xeroradiography, optical memories, optical circuits, photoresists, etc.). 

Accordingly over all the composition range from MX to MX2, either the NiAs- or Cdl2-type structure is stable at higher temperatures. A number of papers have been published on 3d-transition metal chalcogenides from the viewpoint of order-disorder of metal vacancies. A study of the V-S system from this point of view is described here. 

The transition element chalcogenides studied by Haraldsen and coworkers (5) and by Jellinek (9). The former have shown that very many phases exist. Jellinek has pointed out that in the range CrS to Cr2S3 the chromium atoms fit into vacancies in a hexagonal close-packed sulfur frame and in many compounds, the vacancy distribution can be ordered, disordered, or partially ordered. 

In Anderson s treatment, no account is taken of changes in the electronic disorder of the compound arising from changes in the stoichiometry. In the sense of the notation used previously this is equivalent to considering the presence of only neutral defects. For a binary compound exhibiting only Frenkel disorder in the metal lattice, the defects are therefore Vm° and Mf, with no defects in chalcogenide lattice. The presentation given here is equivalent to that of Anderson, since we can write ... 

The R-M-Z-X (M = Cu, Ag Z = Si, Ge, Sn, X = S, Se) systems have been investigated mainly across the R2X3-M2X-ZX2 sections. No quaternary compounds are known for Te systems. Quaternary compoimds that form in these systems are listed in Table 38. Among all of these 105 quaternary chalcogenides only four compoimds crystallize in SG other than P63. In several series of the silver compounds, occupational disorder for the silver atom has been foimd. 

So-called ternary or mixed oxide systems based on the rock salt structure are well established. Thus LiFe02 exists both in a disordered form in which Li and Fe are randomly distributed on the metal sites, and as an ordered variant with tetragonal symmetry. Rhombohedral distortions are found for LiNi02, LiV02, and NaFe02 in which the cations are ordered on different sublattices. The HCP counterpart of the sodium chloride structure, the so-called Nickel Arsenide stucture (5ee Chalcogenides Solid-state Chewistr, is found only for the heavier members of the Oxygen family. 

Chalcogenides. A review has been published in which the disorder of CrS and the order-disorder transitions in Cr S and AgCrSe2 are discussed. The metal 2p- and 3s-orbital ionization potentials in Cr2S3 have been deter-... 

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