Analysis of AC Conductivity Data of the Anion Excess Sr_{1 — x}Th_xF_{2 + 2x} Solid Solution with Fluorite-Type Structure

Conductivity parameters, number of charge carriers, frequency of hopping, have been determined from an analysis of ac conductivity data of the Sr_{1 — x}Th_xF_{2 + 2x} (0 ≤ x ≤ 0.225) solid solution with fluorite-type structure. The charge carrier concentration has been estimated: (i) from the frequency dependence of conductivity, in accordance with the Almond-West approach; (ii) from the increment of the dielectric constant due to charge carriers. Similar results have been obtained by both approaches. The fraction of charge carriers per formula unit, evaluated as a function of composition, is in good agreement with the estimations made on the basis of the clustering process model which assumes that the charge carriers at long range in Sr_{1 — x}Th_xF_{2 + 2x} are interstitial fluoride ions of F′′′ type. For x > 0.05, the results have been interpreted by the additional presence of nn and nnn dipoles, the concentration and reorientation rate parameters of which have been evaluated.