Abstract
The audio-frequency dielectric constant has been determined over the temperature range 5.5-400K for various samples of calcium fluoride doped with lithium, sodium, potassium and rubidium. A distinct, alkali-metal-associated relaxation is observed in each case. The activation energy for reorientation is largest for the sodium dopant. A physical argument based on ion size is given supporting the assignment of the principal peaks to substitutional alkali-metal-nearest-neighbour fluorine vacancy pairs. It is noted that the current interpretation is consistent with the empirical observation that in all materials studied to date the energy for reorientation of a bound interstitial or vacancy around a substitutional ion is less than or equal to the energy for motion of the free species. Finally, it is pointed out that anion-excess materials have a stronger tendency to form impurity clusters than do anion-deficient materials.
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