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 th e ac-conductivity data took into account contributions of Cole-Cole dielect ric relaxation of dipoles (vacancy-impurity cation pair associates), Almond -West relaxation of charge carriers (cation vacancies) and electrode effect s in the form of modified Warburg impedance. Results of the analysis show t hat the high-frequency conductivity of doped NaCl is completely due to the dipole relaxation. The dipoles concentration was estimated as 25-50 ppm sli ghtly increasing with temperature in the temperature range 120-220 degreesC in accord with the expected one from the classical Schottky-Wagner approac h. No sign of Jonscher's 'Universal Dielectric Response' was detected in th e samples studied. Within experimental error the dipole relaxation peaks ar e of ideal Debye form. (C) 2000 Elsevier Science B.V. All rights reserved.