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

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The EPR spectra of Ag²⁺ ions in CdCl₂ and CdBr₂ 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 CdCl₂ : Ag²⁺ and between 98 K and 213 K for CdBr₂ : Ag²⁺. The transition temperature for CdCl₂ : Ag²⁺ 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 CdBr₂ : Ag²⁺ 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.