Some factors governing Ag+ and Cu+ low coordination in chalcogenide environments

The factors influencing the low coordination of Cu+ and Ag+ d(10) cations i n chalcogenides are analyzed by means of FLAPW band structure calculations. The study shows that the metal sid orbital mixing is the predominant facto r, in agreement with most previous research reports. It also quantitatively shows that the d(10) cation polarization is reduced when the chalcogen ele ctronegativity decreases, thus the coordination increases when going from t he oxides to the tellurides. The calculation results make clear the fact th at the d(10) element low coordination can be raised for a given chalcogen b y enhancing the polarization influence of the chalcogen through a charge tr ansfer from an alkali metal. Finally, the shift in behavior from Cu+ to Ag is shown to be related to their different polarizabilities. (C) 2001 Acade mic Press.