ON THE POSSIBILITY OF A FORECAST FOR OFF-CENTER CONFIGURATION OF AG+ AND CU+ IN ALKALI-HALIDE CRYSTALS

The simple cut criterion based on the accurate determination of the radii of the ions in alkali halides and previously introduced by the authors for forecasting off-centre configuration of Li+ and F- has been extended to heavy ions (Ag+ and Cu+). It has been found that this criterion is valid for the Ag+ ion, whereas for Cu+ gives a less precise forecast because of the lack in knowledge of the effective partial charge on Cu+ ion. It has been evidenced that the critical value of the ratio r + * /r + between impurity and host ion radius which allows off-centre configuration is dependent on the impurity ion mass. © 1990 Societá Italiana di Fisica.