Dielectric relaxation studies of alkali-metal-doped calcium fluoride

Dielectric spectra of doped and X‐ray irradiated calcium fluoride crystals

“…The activation parameters of the relaxation process are determined using the method described in [3][4][5][6] and are given in Table 1. Table 1 Activation energy, E (eV), and reciprocal frequency factor, τ 0 (s), for principal relaxation observed in the studied crystals; the obtained values are comparable with those reported by [11][12][13].…”

“…The relevant ionic radii are 1.06(Li + ), 1.26(Ca ++ ), 1.32(Na + ) and 1.33 (Pb 2+ ) Å, showing that while sodium and lead is closest in size to calcium, lithium is smaller. Thus, one might expect that the reorientation process in the lead-doped and sodium-co-doped material, where minimum distortion occurs would have higher activation energy than in lithium-codoped crystals [11], as can be observed in Table 1. There are no considerable differences between the dielectric behaviour of the various doped and co-dopedsamples probable because the amount of the alkali-metal in the samples is too small in comparison with PbF 2 .…”

“…The temperature T max is shifted to higher value for doped and codoped, and also for x-irradiated samples in comparison with pure CaF 2 . It has been established [11] that in the case of alkali-metal doped calcium fluoride, the main relaxation is associated with a substitutional alkali-metal ion and a nearest-neighbour fluorine vacancy.…”

Physical basis of fragility

“…21 On the other hand, no evidence of clusters is found in alkali metal doped alkaline earth fluorides. 22 ͑In the alkaline earth fluorides, the simple defects are also immobile.͒ These are a few examples of an extensive literature that exists concerning defects in solids and their interactions.…”

Association and bound motion in alkali-metal-doped cadmium fluoride

“…The mobility is given by1 3 " = (e r 2 a /kr) exp (-gf'kT) (6) where r is the jump distance, va is the attempt and the pre-exponential factor °o is…”