Reorientation of trivalent cation-interstitial fluorine pair in CaF2

Abstract

Anelastic relaxation measurements are reported for CaF₂ containing 0.45 mol percent GdF₃ as a function of heat treatment of the crystals prior to measurement. Two main relaxation modes were found whose intensities were influenced by heat treatment in the same way as were tetragonal centres observed in the EPR spectrum. Treating these centres as pairs formed of Gd³⁺ ions plus nearby F^- interstitials, a two shell relaxation mode analysis accounts quantitatively for the relaxation times observed by anelastic and dielectric relaxation and by EPR linebroadening. An additional relaxation mode, excited by longitudinal stress, was observed but not identified. It was uninfluenced by heat treatment.