Anelastic and dielectric relaxation of LiF-doped MgF2crystals

Abstract

The defect structure of LiF-doped (tetragonal) crystals of MgF2 is determined from a study of anelastic and dielectric relaxation, employing samples with various characteristic orientations. No loss peaks are found, except in the case of internal friction of (100)-oriented samples, for which a Debye peak is observed at -53 degrees C for a frequency of 8 kHz. It is established that this peak is due to an Li-Li interstitial pair which replaces a single Mg2+ ion and resides on a (001) plane. The activation enthalpy for relaxation (0.41 eV) is attributed to the rotational flip-flop of the pair between two equivalent orientations.