Estimation of the charge carrier concentration in NaCl single crystals from analysis of the frequency dependent conductivity

In this article ac-conductivity was analyzed of NaCl single crystals doped with bivalent additive Co2+ in low concentrations (500 ppm). Analysis of the ac-conductivity data took into account contributions of Cole–Cole dielectric relaxation of dipoles (vacancy–impurity cation pair associates), Almond–West relaxation of charge carriers (cation vacancies) and electrode effects in the form of modified Warburg impedance. Results of the analysis show that the high-frequency conductivity of doped NaCl is completely due to the dipole relaxation. The dipoles concentration was estimated as 25–50 ppm slightly increasing with temperature in the temperature range 120–220°C in accord with the expected one from the classical Schottky–Wagner approach. No sign of Jonscher’s ‘Universal Dielectric Response’ was detected in the samples studied. Within experimental error the dipole relaxation peaks are of ideal Debye form.