FREQUENCY-DOMAIN DIELECTRIC STUDIES IN LIFCA2+

Dielectric losses and conductivity studies in LiF:Ca2+ crystals were performed in the dissociation region in the frequency range from 5 to 500 kHz. Two dipolar contributions are revealed. The energy parameters of the high-frequency loss peak evidences the rotation of an impurity-cation vacancy dipole by NN --> NN jumping of the bound-cation vacancy. This result is in agreement with previously reported ionic thermocurrent data of ours and directs us to the conclusion that the migration enthalpy of the bound cation vacancy decreases as a function of the ionic radius of the impurity.