EPR Studies of Strong Jahn-Teller Coupling Systems CdCl2: Ag2+ and CdBr2: Ag2+

The EPR spectra of Ag 2+ ions in CdCl 2 and CdBr 2 are investigated in the temperature range from 4.2 K to 306 K. Low temperature spectra, exhibiting static tetragonal Jahn-Teller distortions, are observed below 77 K. The transition from the low temperature spectra to the motionally averaged high temperature ones is observed between 97 K and 170 K for CdCl 2 : Ag 2+ and between 98 K and 213 K for CdBr 2 : Ag 2+ . The transition temperature for CdCl 2 : Ag 2+ depends on the orientation of the crystal and on the position of the super hyperfine line in question, which is explained by the motional averaging model. The anisotropy of the g -value of the low temperature spectrum of CdBr 2 : Ag 2+ is found to be extraordinarily small ( g // =2.072, g ⊥ =2.067 at 77 K). The reasons for this small anisotropy of the g -value are discussed.